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Soviet Sniper · Joined: 09 Nov 2004 Posts: 1081 Location: Edina MN

I have this problem, I think it started as I went 24v on my E30. Now that I changed the differential last week it became more apparent.

When I first start moving on a cold drive-train (I always warm my engine), the car jerks when I release gas. I is very annoying when I shift the gears and no matter how smooth I am with the clutch and gas, it always jerks at the point when gas is released, like something is lagging and the engine violently slows the car down for a split second. It goes away after some driving.

What can that be? I have 2 ideas, either clutch issues, or brake issues.

My brakes seem to be old but fine. I do not notice any abnormal noise or smell such as if they were stuck and caused that jerking when gas pedal is released. The car also rolls in neutral pretty fine Smile

The clutch makes squeaking noise when the pedal is pressed, but seems to work alright as well. I do have a problem when the car sometimes will not go into the 5th gear unless I hold it in place when releasing the clutch pedal. Then it works fine. So I guess my clutch/transmission was somewhat hard driven, or the shift linkage is worn.

Not sure if the symptoms are related but I am leaning toward clutch problems. What specifically can that be?
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1988 325is | 199k+ | First car (now s52 powered) Cool

1992 Saab c900 | 200k+ | Winter vehicle
1982 Virago xv920j | 25k+ | Cool

m78 · Posted: Fri Jul 29, 2011 10:49 pm Post subject:

Unless your shoes are wet, your clutch should not make a squeaky sound.

Probably the first signs of the slave cylinder going bad. pretty cheap to replace.

If the clutch ever begins to stick on the floor board, then you definitely need to replace the slave, but don't wait until that happens.
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Lachssilber Metallic 203 1988 325i sedan with 200,xxx miles

Top Speed 220 km/h

(OO=00=OO)

Soviet Sniper · Joined: 09 Nov 2004 Posts: 1081 Location: Edina MN

Sure...

But what about that jerking thing? I can not figure out how a clutch would cause this. Like when I drove the car yesterday it did not happen at all for some reason.

I spoke to my grandpa (mechanical engineer) he said it is just the totality of cold drive-train (bearings, oil, etc.) that puts an extra strain on the engine not allowing the car to roll more freely and that's why the jerking/braking is happening. I guess that is possible if it was -10F outside, but right now I don't buy that idea. Rolling Eyes

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1988 325is | 199k+ | First car (now s52 powered) Cool

1992 Saab c900 | 200k+ | Winter vehicle
1982 Virago xv920j | 25k+ | Cool

m78 · Posted: Sat Jul 30, 2011 9:01 am Post subject:

My guess would be the fact that the slave may be failing, may cause a slight delay in the hydraulic piston in the slave from depressing and/or expanding properly. Therefore causing a delayed reaction in the clutch plate engaging.

Either that or you have a failing throw out bearing.

Does the engine rev while the jerking is going on?
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Lachssilber Metallic 203 1988 325i sedan with 200,xxx miles

Top Speed 220 km/h

(OO=00=OO)

Soviet Sniper · Joined: 09 Nov 2004 Posts: 1081 Location: Edina MN

No, the engine is slowing down at the time. I release gas and the car jerks because it is being violently slowed down by the engine. Like if it remains in gear and the engine turns off on you. This happens both when I simply release the gas while in gear and when I shift gears (because I am simultaneously releasing gas as I press the clutch).
Normally when you release the gas in gear the car slows down with the engine but very smoothly, not readily noticeable the same split second. Here it does that to cause discomfort of being thrown forward in the seat because of a sudden slowing down. Very Happy

Like I said, sometimes the car does this when I start driving, and then goes fine. Sometimes it does not do it at all through the whole day. Rolling Eyes

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1988 325is | 199k+ | First car (now s52 powered) Cool

1992 Saab c900 | 200k+ | Winter vehicle
1982 Virago xv920j | 25k+ | Cool

haber · Joined: 14 Jun 2002 Posts: 1663 Location: Tennessee

I'm going a different direction altogether. It sounds to me like your throttle plate is off from where your idle control wants the idle to be or the TPS is adjusted well off idle. The newer 3 wire ICV has a 'home' position it will return to every time the TPS opens and then a control position that varies as it sets the idle when the TPS is closed. Too big a difference and you get this on/off bump. You want a smooth on/off idle transition when the TPS contact changes. If not, every time you transition on or off idle (TPS contacts open or close) you get an abrubt transition in speed. I have the same problem at times with my S38 but with 6 throttle bodies it's a chore to tweak it.

Try this, when the engine is warm and there is no load simply unplug the TPS. If the idle jumps up you need to close the throttle plate slightly, if it slows down you need to open it up. You want the idle the same whether the TPS is telling the ECM to idle or not. Then you'll need to readjust the TPS for closure just at the point of idle when the throttle closes. This will give you a smooth trnasition on/off idle and the jerk will likely go away.

You might start first by cleaning the throttle plate and ICV well. And, if it will idle OK with the TPS unplugged, try driving it to see if it eliminates this bump. I bet it will.
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beejay · Joined: 18 Nov 2002 Posts: 1158 Location: Eastern, Pa

I agree with Haber.
Sounds like fuel management issues.
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Bob
92 325ic gone Sad

14 BRZ ltd
05 Tundra SR5 TRD
01 VFR800fi - 03 DR650S - 83 CB1100F - 82 CB900F - 69 CB750

Ken Juul · Posted: Mon Aug 01, 2011 12:37 pm Post subject: re

You said worse since the new rear end...possibly something loose back there? How about play in the u joints or the guibo?

Ken Juul · Posted: Wed Aug 03, 2011 8:17 am Post subject: RE

Another thought....I get a jerk when letting off the gas when I run the A/C. Has happened on both my 325ic's, was more noticable with the manual trans.

Soviet Sniper · Joined: 09 Nov 2004 Posts: 1081 Location: Edina MN

You are right, I remember it with my car as well,. It might be the same kind of jerk but much stringer. That makes sense if it is the throttle/ICV issue as was suggested because AC puts strain on the engine and influences idle speed.

Well, I was unable to replicate the problem for a few days now. Maybe it got scared and fixed itself Laughing

Thanks for all the suggestions, I'll keep those in mind when it comes back.
_________________

1988 325is | 199k+ | First car (now s52 powered) Cool

1992 Saab c900 | 200k+ | Winter vehicle
1982 Virago xv920j | 25k+ | Cool