Weird Engine Stutter When Idling? - Bimmerfest

Beats4bimmers · #1 10-29-2012, 06:15 AM

Whats up Everybody! I am the new found owner of a 1990 BMW 525i, I picked it up for $1000 bucks and while it's not perfect, I have brought it back to life at least to daily driver status. It was slow as hell and grumpy at first, struggling to get to 50 - 60 mph even. Paint looks REALLY good minus the rear bumper and a little rust on the bottom passenger side front door.

Front seats need some love, could use a headliner but it's not horrible or an immediate concern. Dashboard and door panels are surprisingly near mint. My brother has a 92' and his door panels are pretty much gone. I have come to the conclusion that someone loved on the car for a long time before giving up on it. Now on to the mechanical issue...

When I first picked it up, the car would give a rough "jerk" when sitting at red lights or stop signs, and sometimes it would even stall but fire back up immediately. Since purchasing a month ago I have replaced the fuel filter, spark plugs, plug wires, intake boot, blower motor and drier filter(has nothing to do with engine issue) all blown fuses, Oil and filter with some restore, a radiator flush because there was straight water in it, and i'm waiting on a distributor cap and rotor.

Since doing all of these things, the car will now at least drive and shift through the gears very smoothly when accelerating. Highway driving will cruise the car along at 80-85 mph with ease. It's when you're in the city and sitting in constant stop and go traffic when all hell breaks loose.

I can't seem to figure out why the car does the jerking when idling, and only when idling. When I reach a red light, I put the car in neutral to keep it from cutting off. But once I'm back in drive, everything's all good again? What do you guys think could be causing this problem? I've ruled out a bad fuel pump since it starts everytime, and usually fuel pumps either work or they don't. It seems more electrical, but outside of the distributor cap and rotor that I'm waiting on, I'm clueless as to where the problem might be coming from. Plus since all of the minor maintenance that I have performed, the jerking is not so bad, kinda intermittent. Its like I have ironed out most of the wrinkles with a few pesky ones left.

Please thrown me some insight! Peace.

BMR_LVR · #2 10-29-2012, 07:05 AM

Welcome to the Fest!

I'm not all that familiar with the M20 engine, but I suspect that your idle control valve either needs to be cleaned (likely) or replaced (less likely).

Do a quick search on this forum for the Bentley manual. It will help you with this and almost all problems you will encounter with these fine automobiles.

Again, welcome.

down19992000 · #3 10-29-2012, 11:44 AM

Quote:

Originally Posted by Beats4bimmers

Whats up Everybody! I am the new found owner of a 1990 BMW 525i, I picked it up for $1000 bucks and while it's not perfect, I have brought it back to life at least to daily driver status. It was slow as hell and grumpy at first, struggling to get to 50 - 60 mph even. Paint looks REALLY good minus the rear bumper and a little rust on the bottom passenger side front door.

Front seats need some love, could use a headliner but it's not horrible or an immediate concern. Dashboard and door panels are surprisingly near mint. My brother has a 92' and his door panels are pretty much gone. I have come to the conclusion that someone loved on the car for a long time before giving up on it. Now on to the mechanical issue...

When I first picked it up, the car would give a rough "jerk" when sitting at red lights or stop signs, and sometimes it would even stall but fire back up immediately. Since purchasing a month ago I have replaced the fuel filter, spark plugs, plug wires, intake boot, blower motor and drier filter(has nothing to do with engine issue) all blown fuses, Oil and filter with some restore, a radiator flush because there was straight water in it, and i'm waiting on a distributor cap and rotor.

Since doing all of these things, the car will now at least drive and shift through the gears very smoothly when accelerating. Highway driving will cruise the car along at 80-85 mph with ease. It's when you're in the city and sitting in constant stop and go traffic when all hell breaks loose.

I can't seem to figure out why the car does the jerking when idling, and only when idling. When I reach a red light, I put the car in neutral to keep it from cutting off. But once I'm back in drive, everything's all good again? What do you guys think could be causing this problem? I've ruled out a bad fuel pump since it starts everytime, and usually fuel pumps either work or they don't. It seems more electrical, but outside of the distributor cap and rotor that I'm waiting on, I'm clueless as to where the problem might be coming from. Plus since all of the minor maintenance that I have performed, the jerking is not so bad, kinda intermittent. Its like I have ironed out most of the wrinkles with a few pesky ones left.

Please thrown me some insight! Peace.

Possibly a vacuum leak? Do you hear a kind of whistling sound when you accelerate?

BMR_LVR · #4 10-29-2012, 11:57 AM

Quote:

Originally Posted by down19992000

Possibly a vacuum leak? Do you hear a kind of whistling sound when you accelerate?

Good call Down.

OP, you can test for this by spraying carb cleaner in the areas of the intake boot and associated hoses while the car is idling. If the idle suddenly goes up, then you have found the area of a vacuum leak.

Beats4bimmers · #5 10-29-2012, 01:20 PM

Hmmm... The intake boot is brand new, but I did not spray the hoses associated with the intake boot when replacing it. I only checked for cracks etc. However, when accelerating, there is no whistling or weird engine noises at all.

The car accelarates perfectly, which to me is weird being that the moment you come to a stop is when the intermittent jerking happens. And it somewhat subsides, I say somewhat because it does not stop altogether, maybe 97% when I put the car in neutral. I assume its because the engine revs a little higher in neutral than it does in drive, so that's what I have been doing when I come to red lights to keep the car from jerking/stalling lol. It's annoying, but it'll have to do until I get this thing figured out.

Luckily the radiator and water pump were already replaced I assume, being that those things look newish. As does the starter. Either way, I love this car, and I have hopes of doing a full restore on it inside and out. Once I get past this jerking issue.

BMR_LVR · #6 10-29-2012, 01:51 PM

Quote:

Originally Posted by Beats4bimmers

Hmmm... The intake boot is brand new, but I did not spray the hoses associated with the intake boot when replacing it. I only checked for cracks etc. However, when accelerating, there is no whistling or weird engine noises at all.

The car accelarates perfectly, which to me is weird being that the moment you come to a stop is when the intermittent jerking happens. And it somewhat subsides, I say somewhat because it does not stop altogether, maybe 97% when I put the car in neutral. I assume its because the engine revs a little higher in neutral than it does in drive, so that's what I have been doing when I come to red lights to keep the car from jerking/stalling lol. It's annoying, but it'll have to do until I get this thing figured out.

Luckily the radiator and water pump were already replaced I assume, being that those things look newish. As does the starter. Either way, I love this car, and I have hopes of doing a full restore on it inside and out. Once I get past this jerking issue.

Your description here again leads me to lean toward a dirty or faulty idle control valve (ICV). However, double check all of the other hoses and spray them with carb cleaner as well. On the M50, The ICV is buried under the intake and pretty difficult to get to without removing the intake assembly (it can be done but is very difficult so I've heard). Again, I'm not too familiar with the M20. It may be easier to get to. Perhaps it would only require a good cleaning. Google "BMW M20 idle control valve cleaning" and you should get some good resources. It may even be on youtube. Also, get a hold of that Bentley manual. It will be extremely helpful.

Good luck and I hope this helps.

EDIT: I pulled up the Bentley manual and on page 113-2, it shows a picture of the idle control valve (#2) on the M20 and looks to be a piece of cake to get to. Page 130-12 tells how to check it.

BMWFatherFigure · #7 10-29-2012, 04:26 PM

+1 on ICV. Leaks don't come and go.

robertobaggio20 · #8 10-29-2012, 05:16 PM

While doing the ICV (which is indeed child's play on the m20, relative to the m50), it might be good to clean out your throttle position switch and its sensor. You merely need contact cleaner for this. It is unlikely to be a contributor to this situation, but it takes less than 5 minutes to do and it occassionally causes some problems so please do get to that along the way.