WTF? Clutch replaced and the car still hesitates...

[Andryuha]

First of all, I own a '93 525i 5spd. Car runs fine at idle, but sometimes RPMs fluctuate a bit. When I take off, car hesitates and stutters - RPMs fluctuate. Car also hesitates when accelerating hard in every gear. What could be wrong? I'm so upset

[DaveVoorhis]

I hope you didn't change the clutch hoping that would fix it, because that ain't it.

Could be a number of things related to fuel, air and spark, but I'd be inclined to see if the ECU is showing any codes (search for "stomp test"), then check maintenance items, like the fuel filter, spark plugs & leads and air filter, then check for vacuum leaks, sticky Idle Air Controller, bad Throttle Position Sensor, fuel pump, fuel pressure regulator, corroded electrical connections to engine sensors and so on...

More details on the symptoms, such as whether it's worse when hot or cold, when the tank is full or empty, etc., would be helpful.

[Andryuha]

ok, i just pulled the coilpacks and found spark plug wells 1 and 6 almost completely flooded with oil. I dont understand how it got there, since I changed the valve cover gasket one year ago.

[DaveVoorhis]

ok, i just pulled the coilpacks and found spark plug wells 1 and 6 almost completely flooded with oil. I dont understand how it got there, since I changed the valve cover gasket one year ago.

Ah hah! That valve cover gasket must be leaking. Warped or improperly torqued valve cover, maybe? Crappy and/or misplaced gasket?

[Andryuha]

hmm, I never knew that the valve cover needs to be torqued properly. I just tightened it almost as hard as i could

[Derek A.]

BMW uses special bolts for the valve cover. Tighten them till they strip - then back them off a 1/4 turn.

[Andryuha]

BMW uses special bolts for the valve cover. Tighten them till they strip - then back them off a 1/4 turn.
till they strip?

[DaveVoorhis]

hmm, I never knew that the valve cover needs to be torqued properly. I just tightened it almost as hard as i could
Bolted assemblies almost always have specified torque ratings whether they're well-known or not. This is especially true of aluminium castings, which are easy to warp. You've squished the gasket and possibly warped the cover. I don't have the torque rating for the M50 engine valve cover to hand, but valve covers in general should be tightened snugly (M6 nuts/bolts are usually about 9 to 10nm) but not as hard as you can. Replace the gasket, check for warpage of the cover, and torque the bolts properly.

[Mitch90535im]

hmm, I never knew that the valve cover needs to be torqued properly. I just tightened it almost as hard as i could
You're kidding, right?

[Alexlind123]

hmm, I never knew that the valve cover needs to be torqued properly. I just tightened it almost as hard as i could

On the M30 engine, the valve cover bolt torque spec feels surprisingly light. Nowhere near as tight as possible, just right at the low end of "snug."

[632 Regal]

maybe he is a small dude?

You're kidding, right?

[Dave M]

hmm, I never knew that the valve cover needs to be torqued properly. I just tightened it almost as hard as i could

This should save you some elbow grease.

Right click and "save as":BMW torque values (http://www.mwrench.com/Whitepapers/torqspec.pdf)
BTW, the M50 valve cover bolts are tightened to 15 NM, as opposed to 290 NM ;)

Dave M

[Andryuha]

This should save you some elbow grease.

Right click and "save as":BMW torque values (http://www.mwrench.com/Whitepapers/torqspec.pdf)
BTW, the M50 valve cover bolts are tightened to 15 NM, as opposed to 290 NM ;)

Dave M

Thank you. And btw, your 535i has 500,000kms? Did you do any major work on it?

[632 Regal]

strippers are cool...

till they strip?

[Dave M]

Thank you. And btw, your 535i has 500,000kms? Did you do any major work on it?

You're quite welcome.

Yes, you might say there was work done this past winter. At 1/2 million km, I found one cylinder with low compression. It still ran great, had power, great mileage, but used some oil. I wanted to learn something and had just built a heated garage so decided to swap out the old engine block with a rebuilt and freshen up the head.

It was an incredible winter project, lots of time to try and do things right. I hope I've 'bought' another 1/2 million kms.

Good luck with your head cover,

Dave M

[Ross]

That's what I call torque to yield!

[Andryuha]

Ok, I replaced the VC gasket and spark plugs. The car ran great for about 1/2 hour, but then the hesitation came back. The weird thing is that it would run fine on a straight road, but once I start hitting bumps or make turns it hesitates. One thing that I noticed when I changed the plugs is that a stud that holds one of the coilpack wast loose. I dont know how to tighten it, so the coilpack is not very secure and moves around a bit. Could that be the problem?

[joshua43214]

There should be 2 studs that hold the coil pack down, and yes they must be tight so that the coil is properly grounded. thread 2 nuts down onto the stud, and tighten them against each other. then tighten the stud by turning the top nut with a wrench. Or use a vicegrip in the unthreaded portion of the stud.

Where is the other stud?

What brand and type of plugs did you use?

Are you sure the intake boots are all tight? no air leaks that pop up when you hit a bump?
Don't drive your car with loose parts.

[Andryuha]

1. There are 2 studs - one of them is a bit loose
2. I use Bosch platinum 2. I had the same ones in for over a year with no problems
3. The intake boots were the first thing I checked - they are all tight

[joshua43214]

1. There are 2 studs - one of them is a bit loose
2. I use Bosch platinum 2. I had the same ones in for over a year with no problems
3. The intake boots were the first thing I checked - they are all tight

I hate to pick at small details, but it seems to me you have problems...

some of the problems you have described can come from botch platinum plugs, but not anything relating to going over bumps or turning.

[BillionPa]

check the coil pack resistance on all coils, also check the boot that goes from the coil to the spark plug, they can cause your problem if they are ****.

[Andryuha]

how do i check resistance on the coilpacks? Also, today I've noticed that the car runs fine until the engine warms up. I was also thinking that those little ground wires on coilpacks could be the culprit...

[BillionPa]

take a multimeter to the 2 input wires on the coilpack.

i would think the boots would be the culprit, since heat would cause them to expand and loose a good connection.

[Andryuha]

is there any way to tell if boots are bad? They all look the same to me - nothing abnormal

[BillionPa]

not sure, someone here mentioned that the inside of a few of his boots looked pretty bad, and that getting new ones fixed all his problems, which were the same type that you are having.