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#1 (permalink) Old 01-15-2004, 10:09 AM
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Occasionally, when chopping the throttle completely off, my RPMs dip down below normal idle speed for a split second. The engine idles rough, as it should at such low RPMs, then returns immediately to normal idle speed - almost as if it wants to stall momentarily. Above Idle, the engine runs normally.

This happens very sporadically and I have not been able to establish any particular circumstances in which it occurs. It doesn't seem to matter if outside temperatures are hot or cold, the heater/air con is running, etc. I entertained the idea of bent valves but to my knowledge, the car has never been lugged or abused in any way. Besides, if it was a bent valve, wouldn't rough idle be a consistent trait?

I'm stumped. The car runs flawlessly other than these random idle hiccups. Any ideas?

Thank you.

'98 M3 4-door (manual) | ~ 67k miles
No engine mods other than removal of the baffle in the air box
UUC clutch stop (properly adjusted)
Driven hard sometimes, but never abused
~ 67k miles

Me - '98 M3/4 (manual)
Estoril on black Nappa, UUC clutch stop, de-baffled airbox, Pilot Sports

Wife - '04 Discovery II
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#2 (permalink) Old 01-15-2004, 10:27 AM
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I also run a 98 m3...

and lets say i arrive at a light or a stop and i put the clutch in... the revs drop because obviously i'm not adding gas anymore and yes...the rpm needle drops "slightly" below the idle point and my car sounds like its gonna stall...but it jumps right back up to idle and runs perfectly.

It's just when i'm getting ready to stop and the rpms drop from like 1.5 or 2 to the idle. Like you said, the needle just slightly passes the idle point and the motor sort of "flutters" like its gonna stall but doesnt.

i think it's normal.
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#3 (permalink) Old 01-15-2004, 10:38 AM
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Quote:
Originally posted by KingScare@Jan 15 2004, 12:07 PM
I also run a 98 m3...

and lets say i arrive at a light or a stop and i put the clutch in... the revs drop because obviously i'm not adding gas anymore and yes...the rpm needle drops "slightly" below the idle point and my car sounds like its gonna stall...but it jumps right back up to idle and runs perfectly.

It's just when i'm getting ready to stop and the rpms drop from like 1.5 or 2 to the idle. Like you said, the needle just slightly passes the idle point and the motor sort of "flutters" like its gonna stall but doesnt.

i think it's normal.
Sounds like you are experiencing the exact same thing. Does it just happen at totally random times and under no certain conditions? "Flutters," as you put it, is a good way to describe it.

It did completely stall on me one time. It was mid-90║ temps outside, the car was up to full-temp and I chopped the throttle while making a hard right into an empty parking lot. It started right back up with no hesitation and ran perfectly thereafter.

My guess is that it is not normal, but I also have a feeling it is something minor that I am overlooking as a possible cause. Maybe TECH has seen it before...

Me - '98 M3/4 (manual)
Estoril on black Nappa, UUC clutch stop, de-baffled airbox, Pilot Sports

Wife - '04 Discovery II
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#4 (permalink) Old 01-15-2004, 10:56 AM
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It happened this summer and it's happening during the winter.

It basically manifests when i put the clutch in getting ready for a full stop and the needle gets the chance to hit the idle point. It just slips by real quick, i hear my motor flutter and then it comes right back up and idles fine.

It never really died on me though. That never happened.
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#5 (permalink) Old 01-15-2004, 01:06 PM
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Quote:
Originally posted by KingScare@Jan 15 2004, 12:36 PM
It happened this summer and it's happening during the winter.

It basically manifests when i put the clutch in getting ready for a full stop and the needle gets the chance to hit the idle point. It just slips by real quick, i hear my motor flutter and then it comes right back up and idles fine.

It never really died on me though. That never happened.
It's good to know I am not the only one. Guess we'll wait to hear from TECH.

Me - '98 M3/4 (manual)
Estoril on black Nappa, UUC clutch stop, de-baffled airbox, Pilot Sports

Wife - '04 Discovery II
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#6 (permalink) Old 01-15-2004, 01:21 PM
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this is a very common problem with all e36's the so called "idle bounce" as we dubed it back in the day of BMWplanet. id like to hear what tech has to say, because there has been so many different theories as to why this happens. mine turned out to be the ICV was sticking a bit. but since has come back, (a year in between) and i know that the sticking ICV isnt always the problem for this particular issue.

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#7 (permalink) Old 01-15-2004, 01:43 PM
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Originally posted by Furious@Jan 15 2004, 03:01 PM
this is a very common problem with all e36's the so called "idle bounce" as we dubed it back in the day of BMWplanet. id like to hear what tech has to say, because there has been so many different theories as to why this happens. mine turned out to be the ICV was sticking a bit. but since has come back, (a year in between) and i know that the sticking ICV isnt always the problem for this particular issue.
I'll be damned. I thought I knew all of the E36 quirks but have never heard of this one.

Thanks for the response.

Me - '98 M3/4 (manual)
Estoril on black Nappa, UUC clutch stop, de-baffled airbox, Pilot Sports

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#8 (permalink) Old 01-15-2004, 10:45 PM
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The most common problem would be the idle air control valve as mentioned by Furious. In many makes of cars, like BMW's, the valve gets carboned up and sticks, so that when the valve is trying to open, there is a delay in it's movement, and the engine stumbles, and sometimes dies. If it's really bad, the engine may start, and simply stall. Most of the time it will surge as it tries to correct. You can take it off, and attempt to clean it with brake clean, or carb cleaner, but there is no guarantee that will work. We always replace them, simply so we don't have to do the same work twice, once to clean, and then again to replace it.
You can also check for any vacuum leaks around the intake boot/hoses, but a leak should set a check engine light.
Other than that, M3's have been finicky about idling when they are cold. There was a software program update for the E36 M3, and there is also one for the e46 M3.
I'd look into those 2 areas.
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#9 (permalink) Old 01-15-2004, 11:05 PM
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Originally posted by TECH@Jan 16 2004, 12:25 AM
The most common problem would be the idle air control valve as mentioned by Furious. In many makes of cars, like BMW's, the valve gets carboned up and sticks, so that when the valve is trying to open, there is a delay in it's movement, and the engine stumbles, and sometimes dies. If it's really bad, the engine may start, and simply stall. Most of the time it will surge as it tries to correct. You can take it off, and attempt to clean it with brake clean, or carb cleaner, but there is no guarantee that will work. We always replace them, simply so we don't have to do the same work twice, once to clean, and then again to replace it.
You can also check for any vacuum leaks around the intake boot/hoses, but a leak should set a check engine light.
Other than that, M3's have been finicky about idling when they are cold. There was a software program update for the E36 M3, and there is also one for the e46 M3.
I'd look into those 2 areas.
That's a load off.

Thanks you for the responses, TECH, Furious. I will check it out this weekend.

Me - '98 M3/4 (manual)
Estoril on black Nappa, UUC clutch stop, de-baffled airbox, Pilot Sports

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#10 (permalink) Old 01-16-2004, 01:32 AM
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Oh, the only way your going to get a bent valve is if you over-rev the engine. Or a component mysteriously fails. You'd definately know it if you bent valves. It would run bad constantly.
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#11 (permalink) Old 01-16-2004, 08:32 AM
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Those software upgrades are available at the stealer right??

And i bet they can tell if it's already installed right? So if i bring it in and it's already on...i won't get charged right??

How much is it if i do need to upgrade?
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#12 (permalink) Old 01-16-2004, 06:13 PM
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Quote:
Originally posted by KingScare@Jan 16 2004, 10:12 AM
Those software upgrades are available at the stealer right??

And i bet they can tell if it's already installed right? So if i bring it in and it's already on...i won't get charged right??

How much is it if i do need to upgrade?
If the car was serviced regularly at a dealer, they should have a record of past repairs. If the programming was done UNDER WARRANTY, then BMW has the record of it, which the dealer can pull up with the "DCS", or Dealer Communication System. You could probably phone them, tell them the last 7 digits of the VIN, and they can pull the report.
There is a good chance that an update is available for your DME, but it may or may not improve the idle quality. It really depends on if the original progamming was done, or not, for the idle problem.
If you bring the car in to have it checked and/or programmed, expect to pay probably an hour labor.
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