E34 idle problem
My 1991 535i has a rough idle. Three of the intake valves were not seating well (discovered with leakdown tester). So I pulled the head and had it redone at a shop. I carefuilly put everything back together and replaced all the vacuum hoses and air hoses. Car runs great but the rough idle is still there. Yesterday i decided to follow some of the advise i read about; I increased the valve lash to .014" and regapped the plugs larger to .035". Now it idles even worse! The coil ohms out OK, but does this indicate that the coil is too weak to send a spark across this slightly larger gap.
There are no air leaks. the engine does not hunt, it simply idles a bit rough (worse now). Spark plugs are the correct silver Boschs. I've adjusted the screw on the bottom of the air flow meter but no obvious change was realised.
Help please.
Major Contributor
Have you cleaned out your Idle Control Valve? It's a common cause of rough/erratic idle.
Measuring resistance in a coil isn't definitive. The problem is that should there be a shorted turn, you'd never know it by a resistance measurement, but you sure WOULD know it in reduced output. I'd be kinda surprised if the coil was bad though. My vote is for a gunked-up ICV.
Thanks for your advise. Here is more info.
I soaked the ICV in carb cleaner for several hours (the valve part not the electrical/solenoid part). It was already pretty clean. The idle control valve is 100% closed when ignition on, somewhere i read it should be 50% open with ignition on-engine off, but I'm not sure that this means i need to replace this expensive part. The idle is a bit rough but not terrible, I would expect worse if the ICV was completly flakey. The other ICV specs are OK, between pin 1-2 and 2-3 I measured 22ohms and between pin 1-3 it is 42ohms.
Throttle position switch tested and meets spec. Closed throttle 6-4 0ohms. Open throttle 5-4 0ohms.
Ignition coil secondary resistance is 9k ohms (measured). Spec is 6K ohms. I didn't think that was far enough off spec to raise a flag but could this be the cause of the poor idle? Idle quality is same whether car is hot or cold.
Other things:
When going slow and hittiung the brakes hard it makes a strong clunking sound from the mid or rear of the car, noticeable from within the car. With the rear lifted off the grond and a helper hitting the bralkes I don't see or hear the problem from under the car, but clunk is still noticeable from within the car. I checked the motor mounts, rear control arm bushings.
Finally the starter or ring gear make a noise at start up. It sounds like a clashing "dring" sound. It disappears when the car catches. What is causing this and can I just ignore it as I've done for the the last year. I start the car everyday and this sound has not changed.
Last edited by erubin; 08-25-2005 at 11:30 AM.
Major Contributor
How did you determine that the ICV was closed at idle? It shouldn't be. It's possible that the throttle plate stop or the TPS is misadjusted. There's a spec on clearance between plate and body, unfortunately, I no longer have the Bentley for the E34, so I can't say what it is (but IIRC it was a few thousandths). Regardless the ICV should be the dominant control over idle speed.
Regarding the clunk, it sounds like the calilpers are moving around when they shouldn't be. Are they loose? And the starter... I think you're gonna have to pull that out to have a look at the pinion and flywheel gears. It doesn't sound healthy at all. This is a very unusual problem with M30s. Those starters usually work perfectly for the life of the car. IMO you should have a look at this sooner rather than later in case the damage is progressing. Better to replace the starter and/or pinion than the flywheel.
<<How did you determine that the ICV was closed at idle? It shouldn't be. >>
Actually I can only check it (easily) with the key on, engine off. That's the way to check, isn't it?
<<It's possible that the throttle plate stop or the TPS is misadjusted. There's a spec on clearance between plate and body>>
This checked out OK. I have the specs so i verified this when I cleaned out the throttle body.
<<Regardless the ICV should be the dominant control over idle speed. >>
Idle speed is not my complaint, nor is it hunting...it is idling rough, sounds like an occasional missfire maybe every 1/2 second or so. When i opened up the spark plug gap (to .036") and valve lash a bit (to .014) the miss even sounded worse.
<<Regarding the clunk, it sounds like the calilpers are moving around when they shouldn't be. Are they loose?>> I"ll check this.
<<And the starter... I think you're gonna have to pull that out to have a look at the pinion and flywheel gears. It doesn't sound healthy at all. This is a very unusual problem with M30s. Those starters usually work perfectly for the life of the car. IMO you should have a look at this sooner rather than later in case the damage is progressing. Better to replace the starter and/or pinion than the flywheel.>>
Agreed and thank you. Oddly, it's not sounding like grinding, more like a ringing sound. Any other thoughts about the idle?
Last edited by erubin; 08-25-2005 at 07:16 PM.
Starter is not making a clashing/grinding sound. Is it possible that the flywheel (its an automatic, not manual) is cracked at the bolt holes? Would this make it sound like a ring. With car off, key on, what position should the ICV be in?
Major Contributor
Mine vibrated under those conditions. That's probably deliberately done to provide a limited diagnostic. Like, if it doesn't vibrate something's definitely wrong. I don't know what, if anything, you can infer if it is vibrating though. That doesn't necessarily mean that it's working correctly. I think you're correct that the cause of the rough idle is elsewhere.
Last edited by SRR2; 09-08-2005 at 05:23 AM.
Super Moderator
As seen here, the bosch silber plugs are not used on the
e34, they are only used on the older e24,e28 m30, The e34 plug is a different plug
The S at the end of the number indicates bosch silber
Originally Posted by erubin
Super Moderator
Are you sure that the cam timing isn't off one tooth when
the head was put back on? As far as the clunk , did you look at the driveshaft center bearing, the rear subframe mounts(beer can bushing) and the diff mounts? Or even the rear axle cv's?
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