1992 BMW 525i M50 engine idle problem

[bissellh]

My 1992 525i E34 M50 has an idle problem, but only after the engine warms up. When the engine is cold the idle is steady right around 600 - 700 RPMS. But, after the engine warms up to normal operating temperature, the idle bounces around between 1000 and 2000 RPMs.

I have no computer fault codes nor do I have a check engine light.

The first thing I did is replace the coolant temperature sensor. It just seemed like the logical place to start since the problem happens when the engine is hot. But, it did not resolve the problem.

I then observed that the hotter it is under the hood, the more the idle bounces around. The problem is not as bad on cold days. It also is not as bad after leaving the hood open for a while, eventhough the engine is still at normal operating temperature.

I checked voltage to the throttle position switch and resistance between the terminals as described in my repair manual. It checked out when the engine was cold and when it was hot.

I also cleaned the AFM with carb cleaner. That did not resolve the problem. I guess I should check the AFM according the my repair manual both at cold and hot temperatures too.

I replaced the ICV(idle control valve) with a used one not too long ago. I do not think it could be the problem. I would like to test it. I am not sure I can access it without removing my intake though.

According to my repair manual, I should also test my intake air temperature sensor.

Can I access my ICV without removing the intake? Where is my intake air temperature sensor? Is there anything else I should be looking at, such as the injectors, engine speed sensor, cylinder identifying sender, etc? Has anyone had a similar experience? If so, how was it resolved?

[Blitzkrieg Bob]

from under the car. just gotta apply some yoga to get into postion.

[BillionPa]

aint that MAF, that thing gets hot right away. if you have a thing of canned air spray it on the crank position sensor when the car starts jumping to see if thats whats causing the problem, if it is, the cold spray will shut it the hell up real fast.

[Blitzkrieg Bob]

aint that MAF, that thing gets hot right away. if you have a thing of canned air spray it on the crank position sensor when the car starts jumping to see if thats whats causing the problem, if it is, the cold spray will shut it the hell up real fast.


upside down

[bissellh]

aint that MAF, that thing gets hot right away. if you have a thing of canned air spray it on the crank position sensor when the car starts jumping to see if thats whats causing the problem, if it is, the cold spray will shut it the hell up real fast.

I will try that. But, first I have to figure out which sensor it is and where it is located on my 1992 BMW 525i M50 engine. According to my repair manual, I have a cylinder identifying sender, sometimes called a camshaft sender. It is located on the timing cover. I also have an engine speed sensor, sometimes called a crankshaft sensor. I am not sure where it is located.

I am guessing the crank position sensor and the engine speed sensor/crankshaft sensor are the same things. Do you know where I can find it on my engine so I can spray canned air on it?

[Blitzkrieg Bob]

Kills the car from the get go...no start just crank.

The fuel pump won't pump with out a CPS signal

[bmwrp8]

O2 sensor? hehehe just a guess check it anyway:D

[bissellh]

Kills the car from the get go...no start just crank.

The fuel pump won't pump with out a CPS signal

Do you think it is worth checking by spraying canned air on it anyway? paerhaps the signal is scewed once it heats up. Do you know where it is located on my 1992 BMW 525i E34 M50 engine?

[bissellh]

Do you know of a way I can check the O2 sensor myself???

[bmwrp8]

Do you know of a way I can check the O2 sensor myself???

I saw that post before on how to check your O2 sensor just do a search but try doing a stomp test or not use a code tool and pull out your codes might just be something else.

[bissellh]

Thanks! I will search the frum on the O2 sensor. I did the stomp test. I have not fault codes and no check engine light or other related dash indicators. I do not think it could be the O2 sensor because it, like the AFM, runs hot anyway. I will not rule it out as a possibility though and will search the forum on it. Thanks again!

[bmwrp8]

Thanks! I will search the frum on the O2 sensor. I did the stomp test. I have not fault codes and no check engine light or other related dash indicators. I do not think it could be the O2 sensor because it, like the AFM, runs hot anyway. I will not rule it out as a possibility though and will search the forum on it. Thanks again!

just try or check your engine bay wirings mine was like that before but its the other way around it has issues when its cold but its fine when warmed up turns up to be my ICV. keep me posted i'm curious also:p

[bissellh]

I cooled the camshaft sender and the crankshaft sensor with carb cleaner to see if that would help the idle problem. It did not seem to help.

I wonder what control/sensor could be affected most easily by outside temperatures.

I also observed that just idling the car in the cold temperatures without opening the hood, helped the idle problem. I previously stated that opening the hood to cool the engine compartment helped the idle problem. Now, I wonder. Perhaps, it was coincidence and the problem is not related to engine compartment temperature at all. Or perhaps it is, and the engine compartment temperature cools down much sooner at idle with the hood closed in colder temperatures.

If engine compartment temperature is unrelated, perhaps it is the oxygen sensor. It is the emission component most exposed to outside air temperatures.

[Morgenster]

I cooled the camshaft sender and the crankshaft sensor with carb cleaner to see if that would help the idle problem. It did not seem to help.

I wonder what control/sensor could be affected most easily by outside temperatures.

I also observed that just idling the car in the cold temperatures without opening the hood, helped the idle problem. I previously stated that opening the hood to cool the engine compartment helped the idle problem. Now, I wonder. Perhaps, it was coincidence and the problem is not related to engine compartment temperature at all. Or perhaps it is, and the engine compartment temperature cools down much sooner at idle with the hood closed in colder temperatures.

If engine compartment temperature is unrelated, perhaps it is the oxygen sensor. It is the emission component most exposed to outside air temperatures.

If you want to reach the ICV it's pretty doable without removing the manifold or going all bendy under the car. You just remove the oil filter cap from the housing to enlarge the space for your left arm. You disconnect the elbow hose from ICV to manifold and take it out first and then disconnect ICV electrical plug en push out ICV through rubber ring. The ICV intake hose is better left on the ICV because it's a bitch to get back on and nearly impossible while under the manifold. I did it and had some trouble getting it back in place but I made it. The procedure can be found somewhere on the net but I can't remember the link. Google will help.
I doubt your ICV is the problem though.

[Ferret]

Idle bounce + No fault codes = usually manifold air leak.

When I bought my first 525i, it used to do this after a rebuild - the usual suspect is the hose that runs to the ICV.

http://www.realoem.com/bmw/diagrams/h/e/6.png

Have a look in the general location of 12 and look for cracks in any part of 10 - that's what was causing idle hunting in mine.

Also watch out for cracking in 3 around where the grommets enter the rubberwork - cracks here can cause problems too.

[bissellh]

Was your hunting idle happening only after the engine warmed up or was it all the time???

[Ferret]

Was your hunting idle happening only after the engine warmed up or was it all the time???

It was only happening after warm up, it'd run happy as larry while cold.

Once warmed up though it was an absoloute bitch, the bouncing combined with the auto box made for fun at a stop light.

I think it's either something to do with ignoring the MAF output during warm up, or something to do with the warmth of the rubber hoses - they become more supple when warmed up and let air leak more. Bullsh*t guess at the temp reason though.

All the air hose rubberwork was shot to crap on my '92 - I'd give yours a thourough inspection, and check for hairline cracks in the rubberwork.

[bissellh]

That sounds like exactly the same problem I am having!

I actually just replaced my engine after my old one overheated while my girlfriend was driving to work. She just kept going until the engine blew up. Needless to say she will not be driving it anymore. My 'new' engine only has 80K compared to the 230K on my car and it pulls very nicely.

I have already fixed some vaccum leaks around the throttle body and AFM. I bet I have some around the ICV too. I have already purchased some fuel line hoses to replace vacuum hoses and some new intake and throttle body gaskets. I bet that if I pull the intake off and replace all hoses and check all fitments it would resolve the problem.

[BillionPa]

... air intake temp sensor test time?

if you dont remember installing a new O2 sensor in the last 70000 miles, replace it now!

[Ferret]

That sounds like exactly the same problem I am having!

I actually just replaced my engine after my old one overheated while my girlfriend was driving to work. She just kept going until the engine blew up. Needless to say she will not be driving it anymore. My 'new' engine only has 80K compared to the 230K on my car and it pulls very nicely.

I have already fixed some vaccum leaks around the throttle body and AFM. I bet I have some around the ICV too. I have already purchased some fuel line hoses to replace vacuum hoses and some new intake and throttle body gaskets. I bet that if I pull the intake off and replace all hoses and check all fitments it would resolve the problem.

With the engine running and the idle bouncing, pull the plug on your MAF and see if it suddenly starts running stable again.

[bissellh]

Wouldn't I be getting a code from the stomp test if this is the culprit?

Regardless, it is probably worth testing the air intake temperature sensor before I tear out the whole intake manifold in order to replace all the vacuum hoses.

Where is it located on my 1992 BMW 525i M50? Repair manual says in air filter housing or intake manifold. The only thing on my air filter housing has two hoses clamped to it. What is that thing anyway? It must be on my intake manifold. Is it readily accessible? Is it left or right of the throttle body? Is it underneath the intake manifold or on the same surface of the intake manifold as the throttle body?

[bissellh]

I have tried that and yes the idle speed drops to around 600 RPM. Additioanlly, I can stop the car and restart it with the AFM unplugged and it will idle at 600 RPM even after I plug the AFM back in. It is a temporary fix though. As soon as I give it some gas the idle jumps up to between 100 and 2000 and bounces around in that range.

[Ferret]

Wouldn't I be getting a code from the stomp test if this is the culprit?


If the MAF totally/electrically fails it'd throw a code warning, but yanking the MAF out of the circuit tells you that this is probably air flow related if the car suddenly starts running properly again.

Yanking the MAF out makes the car default to assumed positions/air/fuel flows - it's also telling you that there's nothing majorly wrong with your ICV as the idle locks down to around 600 RPM quite happily.

Does anyone here know if the ICV is still actively controlling the idle with the MAF removed, or just locked into position and it hopes for the best?

I'd check the parts I pointed out above as they're easy to inspect visually without pulling anything apart :)

[Ferret]

I have tried that and yes the idle speed drops to around 600 RPM. Additioanlly, I can stop the car and restart it with the AFM unplugged and it will idle at 600 RPM even after I plug the AFM back in. It is a temporary fix though. As soon as I give it some gas the idle jumps up to between 100 and 2000 and bounces around in that range.

This sounds exactly what was happening to me, a gentle idle at 600 by pulling the MAF and plugging it back in again. It seemed to be the overrun situation that startes an air leak etc...

After that it'd buck rpm like crazy.

Unless it's something to do with the ECU not rechecking for a MAF until it's revved.

[Morgenster]

Wouldn't I be getting a code from the stomp test if this is the culprit?

Regardless, it is probably worth testing the air intake temperature sensor before I tear out the whole intake manifold in order to replace all the vacuum hoses.

Where is it located on my 1992 BMW 525i M50? Repair manual says in air filter housing or intake manifold. The only thing on my air filter housing has two hoses clamped to it. What is that thing anyway? It must be on my intake manifold. Is it readily accessible? Is it left or right of the throttle body? Is it underneath the intake manifold or on the same surface of the intake manifold as the throttle body?

Just to the right of the throttle body on the manifold you'll see an electrical connector stuck on. Don't confuse with the TPS it's the one right next to it on the manifold. easily accessible.

As for the thing in your air filter box: I have the same thing and no clue what it's there for. The hoses seem stuck to some sort of valve or sensor (no electrical connection near it though). On the inside of the filter box all you see is a protruding metal cilinder. I'm very curious now.

[Ferret]

As for the thing in your air filter box: I have the same thing and no clue what it's there for. The hoses seem stuck to some sort of valve or sensor (no electrical connection near it though). On the inside of the filter box all you see is a protruding metal cilinder. I'm very curious now.

If you check your hose wiring, I think it's a temp valve that opens in cold air situations - it then runs hot coolant around the throttle body to prevent it icing up :)

[Ferret]

As for the thing in your air filter box: I have the same thing and no clue what it's there for. The hoses seem stuck to some sort of valve or sensor (no electrical connection near it though). On the inside of the filter box all you see is a protruding metal cilinder. I'm very curious now.

Attempt 2: Part 10 on this image?

http://bmwfans.info/original/images/58461_p.png

[Morgenster]

Attempt 2: Part 10 on this image?

http://bmwfans.info/original/images/58461_p.png

Exactly that. I love getting to know my engine intimately. Thank you!

[Ferret]

Where is it located on my 1992 BMW 525i M50? Repair manual says in air filter housing or intake manifold. The only thing on my air filter housing has two hoses clamped to it. What is that thing anyway? It must be on my intake manifold. Is it readily accessible? Is it left or right of the throttle body? Is it underneath the intake manifold or on the same surface of the intake manifold as the throttle body?

Air temp sensor is labelled part 13
http://www.realoem.com/bmw/diagrams/k/t/22.png

[bissellh]

"Idle bounce + No fault codes = Air/Vacuum leaks". My problem has been resolved. And the winner is --- vacuum leak!!!

I first checked the air intake temperature sensor and had to removed the throttle body and then inatake manifold to access it. There was 5V to it through the engine harness plug with the ignition on. I checked the resistance across the terminals and it was in the range of the outside air temperature. I breathed on it to warm it up and the resistance went down slightly. I then put in some cold water I had in the trunk and the resistance went up slightly. I would like to have been able to better test it with a wider range of temperatures, but it seemed it was working to specification.

I then turned my attention to possible vacuum leaks. I noticed the vacuum hoses connected to the ICV were not very tight. I did not have replacement hoses handy, so I put hoses clamps on them. I also noticed that the other end of the ICV hose where it connects to the air intake boot had some small cracking, so I put hoses clamps on the both sides of the knuckle that plugs into the air intake boot. I noticed that the two hoses going from the valve cover to the other knuckle on the air intake boot through a connector on the front underside of the intake manifold were not very tight either. Again, I did not have replacement hoses handy, so I replaced them with some 3/8" fuel line from the local auto parts store. The 3/8" was a little snug, but that may keep a better vacuum for longer time anyway. I also replaced the intake manifold and throttle body gaskets while I was at it. I also replaced the small vaccum lines from the intake manifold going to the fuel pressure regulator and the valve cover with new braided cloth covered fuel line for longevity.

When I first started her after repairing all the vacuum leaks she idled at about 750 RPMs. After she warmed up the idle dropped down to 600 RPMs. I don't know if the comnputer was adjjusting or if was a function of the engine temperature. The real test is how she reacted after some spirited driving and exposure to some real heat. She just kept purring at 600 RPMs. Driving down to the stop light at the end of the exit ramp off the highway she just sat right down to 600 RPMs without first bouncing around first.

Thanks for all of your replies and suggestions. I found them very helpful and insightful. It seems to me that if there is an idle problem on an M50 engine without any fault codes or check engine indicators, the problem is probably a vacuum leak, not a sensor. I think it was Ferret first recommended that "Idle bounce + No fault codes = Air/Vacuum leaks".

I really appreciate all of your help becuase my mechanic told me it might take 2 hours or it might take 10 hours to resolve this problem and really cant afford that right now. Besides I found it rewarding to do it myself and learn something along the way.

One question, where can I find those diagrams you attached to your replies???

[BillionPa]

they got em at realoem.com most likely.

good to hear the engine is fixed, and yes its supposed to idle faster during warmup, sounds like your idle is now spot on hot and cold.

[Ferret]

I also noticed that the other end of the ICV hose where it connects to the air intake boot had some small cracking, so I put hoses clamps on the both sides of the knuckle that plugs into the air intake boot. I noticed that the two hoses going from the valve cover to the other knuckle on the air intake boot through a connector on the front underside of the intake manifold were not very tight either.

Heh, glad you found the problem, these hoses were always a nightmare for me.

If I were you I'd go around and slowly replace all the vaccuum hoses as your budget allows - if they're cracked it means they're right at the end of their lifespan and are bound to cause you more trouble in the future.

Links to parts catalogs for your particular car:
RealOEM (http://www.realoem.com/bmw/partgrp.do?model=HD63&mospid=47404)
BMW Fans (http://bmwfans.info/original/E34/Lim/525i-M50/USA/L/A/1992/07/)

Good luck and have fun with the car!