What causes a 1 second hesitation?

[wjbell]

I just took my car out for a spin after regapping the plugs back down to the stock .028. I also put in a new fuel pressure regulator and dumped in some injector cleaner. (as fas as my idle issue is concerned. Both have no effect on idle yet.)

So from a rolling start I give it about 3/4 throttle and there's a huge 1 second hesitation before the engine even responds. I understand being stock it's not suppose to be instantaneous power to the wheels, but this seemed too long of a hesitation to be normal.

What causes hesitation in throttle response?

A little history in case you haven't seen my recent posts... just replaced:

Cap, rotor, wires, plugs fairly new, fuel pressure regulator, valves adjusted within the last thousand miles or so, removed and cleaned ICV and AFM, no vacuum leaks and cleaned the crank position sensor.

Also, it seems like when I changed my cap, rotor and wires the car ran with some different characteristics. Like a little hesitation when you blipped the throttle from idle.

Any ideas?

[525SEI BRIT]

Good question!!

When was the last time the fuel filters were changed, condition of leads, oil seating in plug recesses.

[wjbell]

Good question!!

When was the last time the fuel filters were changed, condition of leads, oil seating in plug recesses.

Fuel filter(s) have not been changed since I've owned the car. Bought it in 5/05 and have put about 5K miles on it. How do I get to the fuel filter? Is there more than one?

Leads? Do you mean spark plugs or wires? Wires are new OEM and plugs are fairly new. The plugs look like they're all burning very clean (not white, not black) and all look the same. No oil on, in or around the plugs at all.

[525SEI BRIT]

flue filters are under the car, right hand side on mine, behind the rear wheel. not sure about the 535 but the 525 had one and the 540 has two. theirs also a strainer attached to the pump inside the tank.

dose the hesitation feel like fuel starvation though, is it burping?!

[dolfan13]

For what its worth my 95 525 was hesitating right off idle.Changed the spark plugs, injector cleaner, new fuel filter no vacuum leaks.Its my daily driver so I was just going to live with it.Did not drive it for about a week gone on vac. came back and battery was dead.This was the third time since I had owned the car,5 months.Anyway put a new battery in it and now no hesitation.Go figure?I did a number of searchs on this subject here but never found where anyone actually fixed it.I guess I got lucky.

[wjbell]

It's possible fuel starvation, but it's not stumbling before taking off. It's like you're rolling off a stop sign gradually picking up speed and the engine is about 1500-2000 RPM, then you punch it. You can literally count "one-one thousand" before the engine responds. But there's no stuttering up to engine response, it's just like dead space. It's like the old Chevy 350, when you punch it you hear the carb sucking in a bunch of air but nothings happening until a second later, then the engine lets loose, if that makes any sense...

Now I haven't tested this thoroughly, and it seems like the more I let the engine "load up" the more it does it. In other words, if I punch it a couple times, the next time I try it it will respond quicker.

[BillionPa]

sounds like the AFM needs lubrication, and check the throttle pos sensor.

[wjbell]

sounds like the AFM needs lubrication, and check the throttle pos sensor.

Thanks. Should I just use something like WD40 on the AFM, or something longer lasting? Since I cleaned it with carb cleaner it might be binding up...

The TPS is working fine. I checked the ohms at closed and just cracking the door open. Seems to be working ok.

[wjbell]

For what its worth my 95 525 was hesitating right off idle.Changed the spark plugs, injector cleaner, new fuel filter no vacuum leaks.Its my daily driver so I was just going to live with it.Did not drive it for about a week gone on vac. came back and battery was dead.This was the third time since I had owned the car,5 months.Anyway put a new battery in it and now no hesitation.Go figure?I did a number of searchs on this subject here but never found where anyone actually fixed it.I guess I got lucky.

Maybe after you changed all those things you needed an ECU reset and the dead battery provided that?

I've reset my ECU twice (well, disconnected the battery for ~20 min) but it doesn't seem to help anything.

[wjbell]

sounds like the AFM needs lubrication, and check the throttle pos sensor.

Well, I just pulled the boot off between the airbox and the AFM and started the engine. The AFM seems to be operating smoothly with no sticking. When moving the throttle it's like there's a cable connected to the AFM. It moves right along with the throttle. I sprayed a little WD in there anyway careful not to get that little electrode thingamabob. ;) But before running the engine I pushed the door open with my finger and it moves smoothly.

[Jeff N.]

The suggestion to check your fuel filter (replace) is a good one. If your car is running lean, you will have low power that might be seen as a hesitation. If lean, you might also notice the surging MPG gauge symptom outlined below.

- when driving at constant speed, mid to light throttle, watch your MPG gauge. Is there any ~ 1 second rthymic back/forth of your MPG gauge?

- how about when you do the same test but this time at with a light acceleration?

Surging of your gauge indicates that the lamda circuit in the car is attempting to do significant corrections of the fuel mixture. This could suggest a bad or slow O2 sensor or an AFM that's out of adjustment.

- speaking of the O2 sensor - do you know it's vintage?

- back to your idle hiccup, have you tried to adjust the AFM idle screw to see if that helps? That can help smooth out a rough idle if everything else is up to spec.

Re lubing your AFM. Well, I've never heard of that. I might like to see a reference in the BMW manual about exactly how you're supposed to do that. I might not do that until someone can cite a correct procedure. Been here a long time and worked on quite a few M30's and this is the first suggestion I've heard for that procedure.

[wjbell]

The suggestion to check your fuel filter (replace) is a good one. If your car is running lean, you will have low power that might be seen as a hesitation. If lean, you might also notice the surging MPG gauge symptom outlined below.

- when driving at constant speed, mid to light throttle, watch your MPG gauge. Is there any ~ 1 second rthymic back/forth of your MPG gauge?

- how about when you do the same test but this time at with a light acceleration?

Surging of your gauge indicates that the lamda circuit in the car is attempting to do significant corrections of the fuel mixture. This could suggest a bad or slow O2 sensor or an AFM that's out of adjustment.

- speaking of the O2 sensor - do you know it's vintage?

- back to your idle hiccup, have you tried to adjust the AFM idle screw to see if that helps? That can help smooth out a rough idle if everything else is up to spec.

Re lubing your AFM. Well, I've never heard of that. I might like to see a reference in the BMW manual about exactly how you're supposed to do that. I might not do that until someone can cite a correct procedure. Been here a long time and worked on quite a few M30's and this is the first suggestion I've heard for that procedure.


Thanks, I will check the MPG gauge tomorrow and post the results.

The AFM idle screw has been mentioned before in my idle post (by you?) I had the AFM out of the car to clean it and I didn't see a screw anywhere. Maybe I didn't look at it close enough... Where is the screw located? I would like to know more about that before adjusting it though.

I replaced the O2 about 6 months ago with an OEM O2. Was getting a check engine light, did the stomp test and that was it. Replaced it and stomp test showed no faults.

[Jeff N.]

...is located on the bottom of the AFM. Remove the AFM and flip it over. Should be next to the inlet side IIR. There may be a cap over the screw you'll need to remove. It adjusts with a hex drive.

Basically, it's an air bleed screw that allows a certain percentage of air around the AFM door. As the idle injector pulse is generally hard set, adjusting this screw will change the idle mixture lambda. This will help fine tune the idle.

To make an adjustment, start the car and slowly turn the screw one direction 1/4 turn at a time until you smooth out the idle. Like any adjustment, be sure to note your starting point.

I bet this will solve your idle lumpiness.

Jeff


Thanks, I will check the MPG gauge tomorrow and post the results.

The AFM idle screw has been mentioned before in my idle post (by you?) I had the AFM out of the car to clean it and I didn't see a screw anywhere. Maybe I didn't look at it close enough... Where is the screw located? I would like to know more about that before adjusting it though.

I replaced the O2 about 6 months ago with an OEM O2. Was getting a check engine light, did the stomp test and that was it. Replaced it and stomp test showed no faults.

[Robin-535im]

It's like the old Chevy 350, when you punch it you hear the carb sucking in a bunch of air but nothings happening until a second later, then the engine lets loose, if that makes any sense...

LOL - been driving my old Chevy 350 a lot lately... I know exactly what you mean

[wjbell]

...is located on the bottom of the AFM. Remove the AFM and flip it over. Should be next to the inlet side IIR. There may be a cap over the screw you'll need to remove. It adjusts with a hex drive.

Basically, it's an air bleed screw that allows a certain percentage of air around the AFM door. As the idle injector pulse is generally hard set, adjusting this screw will change the idle mixture lambda. This will help fine tune the idle.

To make an adjustment, start the car and slowly turn the screw one direction 1/4 turn at a time until you smooth out the idle. Like any adjustment, be sure to note your starting point.

I bet this will solve your idle lumpiness.

Jeff


After I check the MPG gauge and replace the fuel filter I'll try the adjustment. One question though... if it's on the bottom and you have to flip the AFM to get to it, how do you adjust it while running?

Thanks for the help.

[Jeff N.]

..as I'm running a MAF conversion setup.

I seem to recall that you can do it one of two ways.

- use a bent hex key wrench to adjust
- install the AFM upsidedown as you tune. I recall this being difficult as the connection wire was just b-a-r-e-l-y long enough to reach.

You should be able to do this now - fuel filter and MPG gauge really have little to do with the idle quality. The fuel filter would need to be really plugged up to mess with the idle.

Keep at it...we'll get it sorted.

Jeff



After I check the MPG gauge and replace the fuel filter I'll try the adjustment. One question though... if it's on the bottom and you have to flip the AFM to get to it, how do you adjust it while running?

Thanks for the help.

[ber55ber55]

I had the exact same problem.

Check the connectors to the battery terminals...

Then coil....

Fuel filter....

AND LASTLY THE CAT.

With my car it was a mixture of a bad cat and fuel filter.

I took the cat out and cut it open...looked pretty solid.......and the fuel filter had never been replaced AND I ALREADY HAD 120K MILES.

The guy before me did not give a damn about the car.

I also had a bad o2 sensor.

Sensor usually goes bad when the car is running rich....thus causing the sensor to fail.....and then solidifing the cat.

make sure the a/f mix is right as well...

Im not 100% on your problem...but i would say fuel filter or cat in my opinion. Good luck.

[Jeff N.]

Not sure why this might lead to a hesitation...buuut...

Make sure the WOT (wide open throttle) trigger on you TPS actually trips. You'll need to put a meter on the pins to check it. This car doesn't have traction control does it?

The TPS can get gummy inside and you fail to make contact on the WOT trigger. Not much you can do to fix it, pretty well glued together.

Here's a pic of the guts of the TPS I did a while ago; this may help.

http://home.comcast.net/~jsnord/pics/tps.jpg

[wjbell]

Not sure why this might lead to a hesitation...buuut...

Make sure the WOT (wide open throttle) trigger on you TPS actually trips. You'll need to put a meter on the pins to check it. This car doesn't have traction control does it?

The TPS can get gummy inside and you fail to make contact on the WOT trigger. Not much you can do to fix it, pretty well glued together.

Here's a pic of the guts of the TPS I did a while ago; this may help.



Ok, thanks. No traction control, but mine has the six pin TPS. See pic in link:

http://www.belletc.net/test/tps.jpg

Someone else gave me this to test it:

"I found in Bentley there are two different types shown. The three terminal (mine) and the 6 terminal (Yours). If you look closely at the terminals you should see that they are numbered. 1-6. You want to check the ohms between terminal 4 and 6. There should be continuity (zero ohms). then, you can check wide open throttle between 4 and 5 and this should be zero ohms when the throttle is wide open."

I checked it the other day and it was doing something between 4 and 6, either at 0 ohms when just coming off closed, or was at 0 ohms before I moved the throttle, I can't remember. But I just checked 4 and 5 and there is no change in ohms at WOT.

So if I'm testing it right this could be my hesitation problem. Can you confirm that this is the correct test for this type of TPS?

[wjbell]

from the TPS are no continuity between pins 1 and 3 until WOT and then it reads 409 ohms.

Between pins 2 and 3 I get 465 ohms at closed throttle and as I open up the throttle the ohms rise with it up to above 2000 ohms.

[wjbell]

- back to your idle hiccup, have you tried to adjust the AFM idle screw to see if that helps? That can help smooth out a rough idle if everything else is up to spec.



Today I tried the AFM adjustment. It was barley snug at first. I moved it a little one direction, then the other expecting to hear a change but nothing happened. So I rotated it about 3/4 or a turn each direction, still no change.

Now the screw seems like it has no resistance at all, like it can just back itself out with engine vibration... which makes me wonder if it has already backed itself out from wear and the adjustments I'm trying to make are useless... which would make sense of my idle roughness and hesitation. I don't know.

Does anyone know how to adjust the AFM mixture screw? Like 3 1/2 turns out from fully seated as a starting point, or tighten it up until the engine runs rough then back it out x amount of times? Can anyone reference the Bently on this?

[Jeff N.]

...later tonight. That should give you a starting point.



Today I tried the AFM adjustment. It was barley snug at first. I moved it a little one direction, then the other expecting to hear a change but nothing happened. So I rotated it about 3/4 or a turn each direction, still no change.

Now the screw seems like it has no resistance at all, like it can just back itself out with engine vibration... which makes me wonder if it has already backed itself out from wear and the adjustments I'm trying to make are useless... which would make sense of my idle roughness and hesitation. I don't know.

Does anyone know how to adjust the AFM mixture screw? Like 3 1/2 turns out from fully seated as a starting point, or tighten it up until the engine runs rough then back it out x amount of times? Can anyone reference the Bently on this?

[Martin in Bellevue]

LOL - been driving my old Chevy 350 a lot lately... I know exactly what you mean
Why not rebuild the accelerator pump on the carb?

[Robin-535im]

Why not rebuild the accelerator pump on the carb?
My homeowners association only allows one junker heap per house... right now that's the e34. Once I get that off cinderblocks, the truck is next in line. :)

[bill g]

wjbell the original factory setting for the AFM bypass screw is usually stamped in the metal near the screw.
From memory the figure given is the depth from the face of the screw hole to the top of the screw head in millimetres. That would be a good point to start adjusting from.
Screw it in (clockwise) to richen the idle mixture, screw it out to lean.
It should not be necessary to adjust more than a half to one turn unless the AFM is really worn out or someone has messed with the main spring or contact arm in it.


Bill G

[Podmore]

Just spent an interesting few minutes reading through these posts - exactly the same problem I'm having with my '88 535. A momentary hesitation off idle, but it's not always there, and sometimes it's really bad to the point it's burping and farting and you're looking at the truck you're just trying to turn in front of coming at you and you can see the driver's eyes getting big and his mouth forming the words WTF ... and then it comes back to life and takes off like a scalded cat. I suspected TPS but I keep coming back to AFM. Had it apart a few weeks ago to find the little semi-circular slide in the electronics box all gummed up with crap and it worked OK after I cleaned it, but now I'm getting these occasional glitches again. Keep up the good work guys, I'm constantly amazed at how many things can go wrong with my E34 and how many solutions have already been found!

[wjbell]

Just spent an interesting few minutes reading through these posts - exactly the same problem I'm having with my '88 535. A momentary hesitation off idle, but it's not always there, and sometimes it's really bad to the point it's burping and farting and you're looking at the truck you're just trying to turn in front of coming at you and you can see the driver's eyes getting big and his mouth forming the words WTF ... and then it comes back to life and takes off like a scalded cat. I suspected TPS but I keep coming back to AFM. Had it apart a few weeks ago to find the little semi-circular slide in the electronics box all gummed up with crap and it worked OK after I cleaned it, but now I'm getting these occasional glitches again. Keep up the good work guys, I'm constantly amazed at how many things can go wrong with my E34 and how many solutions have already been found!

Yeah, this board is a great resource and there's a lot of knowledgeable people here. I'm kind of afraid to mess with the AFM. Like you said there's so many things that can go wrong. It seems like the adjustment on my AFM has no effect so I'm thinking it could be the problem, but then it could be something else causing the AFM not to respond. I just don't know enough about it. And my wallet's getting thin buying parts that don't need replacing...

[wjbell]

The suggestion to check your fuel filter (replace) is a good one. If your car is running lean, you will have low power that might be seen as a hesitation. If lean, you might also notice the surging MPG gauge symptom outlined below.

- when driving at constant speed, mid to light throttle, watch your MPG gauge. Is there any ~ 1 second rthymic back/forth of your MPG gauge?

- how about when you do the same test but this time at with a light acceleration?

Surging of your gauge indicates that the lamda circuit in the car is attempting to do significant corrections of the fuel mixture. This could suggest a bad or slow O2 sensor or an AFM that's out of adjustment.

- speaking of the O2 sensor - do you know it's vintage?

- back to your idle hiccup, have you tried to adjust the AFM idle screw to see if that helps? That can help smooth out a rough idle if everything else is up to spec.

Re lubing your AFM. Well, I've never heard of that. I might like to see a reference in the BMW manual about exactly how you're supposed to do that. I might not do that until someone can cite a correct procedure. Been here a long time and worked on quite a few M30's and this is the first suggestion I've heard for that procedure.

Checked the MPG gauge for surging and it doesn't surge under any conditions.

I'm disconnecting my battery all day while I'm at work to see if the ECU needs a long time without power to reset. I'll probably change the fuel filter after that. If that doesn't help it's going to the shop. I have a local shop in Sacramento where I live that's a pretty good indy. Schatz & Krum, if anyones heard of it. I'm going to have them check the whole system, AFM adjustment, etc.

[Jeff N.]

Run it all the way in and back out 1 and 1/2 turns. Not saying that's the perfect position, just where mine was when the AFM was pulled off the car.

Jeff



Checked the MPG gauge for surging and it doesn't surge under any conditions.

I'm disconnecting my battery all day while I'm at work to see if the ECU needs a long time without power to reset. I'll probably change the fuel filter after that. If that doesn't help it's going to the shop. I have a local shop in Sacramento where I live that's a pretty good indy. Schatz & Krum, if anyones heard of it. I'm going to have them check the whole system, AFM adjustment, etc.

[wjbell]

Run it all the way in and back out 1 and 1/2 turns. Not saying that's the perfect position, just where mine was when the AFM was pulled off the car.

Jeff

I found this site that explains the AFM adjustment. It's pretty detailed and seems like he has a good working knowledge of the AFM... more than I'm willing to put into it ;)

http://mysite.verizon.net/vzerdcib/e34a/id6.html

I replaced the fuel filter today. Mine was dirty, but chunks weren't falling out of it or anything. It does seem to accelerate a little smoother though.

Well hell, I've replaced every tune-up item I could. Time to go into the shop for a diagnostic. I'm going to have them specifically check for vacuum leaks, the TPS for faults, adjust the AFM and generally look for any failures in the engine systems. I'll post the results.

On a side note... I heard Bruno sells a MAF conversion and you mentioned you have a MAF. How much does it cost to put a MAF on my 535? I saw something where you had to run a separate tuning box where you adjust your own air/fuel mixture. Is there a MAF conversion that's just "plug & play", if you will for the 535?

[Jeff N.]

Between me and Martin, we could likely write a small book on the topic.

The short version is - there ain't no plug and play maf conversion for our cars.

The revised version may read: A company called Miller Performance has a great plug and play MAF solution.

The revised version is in draft form waiting for feedback from the audience.

Bruno no longer sells a MAF conversion I believe; I purchased his only unit and it's what's on my car. His supplier is no longer in business. Maybe he has a new solution?



I found this site that explains the AFM adjustment. It's pretty detailed and seems like he has a good working knowledge of the AFM... more than I'm willing to put into it ;)

http://mysite.verizon.net/vzerdcib/e34a/id6.html

I replaced the fuel filter today. Mine was dirty, but chunks weren't falling out of it or anything. It does seem to accelerate a little smoother though.

Well hell, I've replaced every tune-up item I could. Time to go into the shop for a diagnostic. I'm going to have them specifically check for vacuum leaks, the TPS for faults, adjust the AFM and generally look for any failures in the engine systems. I'll post the results.

On a side note... I heard Bruno sells a MAF conversion and you mentioned you have a MAF. How much does it cost to put a MAF on my 535? I saw something where you had to run a separate tuning box where you adjust your own air/fuel mixture. Is there a MAF conversion that's just "plug & play", if you will for the 535?

[Denasti]

Did you ever get a solution to this?

I have the same exact problem and its gotten to where the car is undriveable. I have checked the pressure from the fuel pump and it seems a bit low at 38 lbs instead of 43 lbs but I disconnected the vacuum line to build up more pressure and it still hiccups when idleing.

I am going to invest in some new Magnaflow cats on monday and a Fuel pressure regulator. I am also going to buy the DME and Fuel pump relays just in case.

[misfortune]

Did you ever get a solution to this?

I have the same exact problem and its gotten to where the car is undriveable. I have checked the pressure from the fuel pump and it seems a bit low at 38 lbs instead of 43 lbs but I disconnected the vacuum line to build up more pressure and it still hiccups when idleing.

I am going to invest in some new Magnaflow cats on monday and a Fuel pressure regulator. I am also going to buy the DME and Fuel pump relays just in case.

I had this problem on my m20, it was my ECU. I have this problem now on my 535i and I bet its my ECU. I'll know soon. I'd try to change it with the same pn.

[632 Regal]

intake leak.

[shurton]

intake leak.

+1

i had similar symptoms, and it was the intake manifold gasket

[genphreak]

intake leak.+2, unless the gap is wrong. If you are not so familiar with gapping plugs, check this with someone who is. I've done this with the wrong setting (.03 out), then realised and re-gapped them to find the problem gone: Motronic has funny ways of dealing with incorrect settings.

Re the AFM adjustment, you've better off not messing with it (unless others have before you) and fixing things that are the cause and not a symptom... :) Nick

[Denasti]

No chance. I have had that thing redone twice. Once by a shop that stunk then I redid it myself and have tested it for leaks via a propane check. Besides a intake leak will kick back a Code for vacuum leak. This has no code?

I replaced the Fuel regulator today and the DME and O2 relays just incase. Still no change, Figures. The Fuel pressure is perfect though which is one less thing to worry about.

I will double, triple check my intake manifold for certain. The Vacuum is hovering around 14 then will slowly drop and stall the car. It never really rises over 14 even under a load. I also can pull the oil cap and it will stumble a bit telling me unlikely a vacuum leak.