Idle begins surging and then car dies

[ckahl2]

Ok, so I'm new here and new to BMW's in general (been a Jeep guy for a while) but I picked up a 1985 325e fairly recently and I've been having some issues with it. I checked the forum and didn't find any issues exactly like mine. So, the car for the most part will start up fine, but not long into driving it the idle starts to bounce a little. Not a lot, Maybe from 400-600 rpm, but it gets worse and worse until the car starts shaking and bucking while it's in gear and then it just shuts off. It won't start back up after with the key (no noise at all from the starter, almost like a dead battery), but it can be bump started, although it won't run for long and the same issues arise.
The car sat for some time during its life, so I replaced both fuel pumps and the tank because they were in really bad shape and I thought that's why it was dying, but the problem continues. Sometimes it will start back up if it's left overnight, sometimes it won't, and most recently I had to call a friend to come help me after it died in the road while I was testing the new pumps. This time it started back up after we attached a battery booster, but the idle problem was still there (although I was able to make it back). I'm thinking it could be the alternator, but I wanted to see if anyone has had these same type of issues before.

[Tim-sutherland]

Mine used to surge and sputter after starting until it warmed up, if I didn't give it enough gas at cold start it would nearly die. I had a questionable icv hose and air boot, so I changed those out. When I was changing I cleaned the inlets of the icv, throttle body and maf with denatured alcohol, and everything was really greasy, so I concluded that I had a vacuum leak and all sorts of crap was getting sucked in.

After that, car started better mostly with only slight surging, so I got some afm cleaner and carb cleaner and removed and cleaned the icv and afm and now it runs great.

So I'd say probably vacuum leak, or dirty / faulty icv or potentially maf, based on my experience.

[Das Delfin]

Use a multimeter to check your battery voltage? With the car off, the batt should read about 12.6 on a full charge, and 12.3 on a low charge. With the car on, it should be around 13.5v. Maybe your voltage regulator is going bad? Does the battery light in the dash turn on when you turn the key to the on position?

[long tall eta]

possibly your idle control module.

[ckahl2]

Thanks for the insights guys. The car actually does fine on startup, it seems like it only has problems after warming up a few minutes, which seems to be the opposite of the problem almost everyone else has had. I'll check the battery after I get off work this afternoon if I can get the car started. The battery light doesn't come on with the key in, engine off, which is what first lead me to believe alternator issues, but the car is old and I haven't had it long, so it could be a burned out bulb or electrical gremlin that's stopping it from being on.

[Das Delfin]

^ a burned out alt bulb prevents the alt from charging the battery

[ckahl2]

I didn't know that bulb was tied directly into the circuit. In case anyone's interested it was burned out and I replaced it, everything seems to be good now. Thanks for the help!

[ckahl2]

Well, unfortunately I'm not out of the water yet. Fixing that bulb also got all of my gauges working (only the tach and ocassionally the temp gauge worked when I bought it), but as I was driving it earlier the Speedo and econometer dropped out at the same time (I assume the other two as well, but it's tough to say when they Stay at a fairly constant value), then my bouncing idle problem returned, again only after the car was warmed up. Luckily this time the alternator issues weren't present, so i can start the car and it comes back to life. While in gear it seems fine, and if I keep my foot a bit in the gas I can keep it alive, but it still wants to die at idle. If I have time tonight or tomorrow I'm gonna look at the idle control valve. Could anything else cause this problem to be connected in some way to the gauges?

[Das Delfin]

There's lots of threads about the idle control valve going bad. My car idles terribly when it's below freezing and sometimes I have to hold the throttle at 2k rpm for half a minute for it to get a clue. My guess would be get at the ICV and clean it and check out your intake rubber and see if you have any leaks... but again I haven't taken mine apart yet so I dunno ;)

There's a few threads about it up on the board right now. It's possible your problem could be a mixture of problems so I'd just start cleaning and see what happens!

[ckahl2]

This car just seems to get more and more interesting. Cleaned the ICV and took it around the block. That didn't seem to do much of anything, but I found some vacuum lines that should be replaced, hopefully that'll do the trick.

The weird part - I filled up at a station while taking my test drive and the gas gauge decided to work again for whatever reason, so now I'm only left with the mystery of the speedometer and econometer. Also, I had thought the OBC led strip was burned out, but it got really bright back when all of the gauges were working for one glorious mile, but now its gone back to being dark, although it seems to be reading information. I have a reasonable range and average MPG so that's a plus I guess? Anyways, the plot thickens...

[long tall eta]

This car just seems to get more and more interesting. Cleaned the ICV and took it around the block. That didn't seem to do much of anything, but I found some vacuum lines that should be replaced, hopefully that'll do the trick.

The weird part - I filled up at a station while taking my test drive and the gas gauge decided to work again for whatever reason, so now I'm only left with the mystery of the speedometer and econometer. Also, I had thought the OBC led strip was burned out, but it got really bright back when all of the gauges were working for one glorious mile, but now its gone back to being dark, although it seems to be reading information. I have a reasonable range and average MPG so that's a plus I guess? Anyways, the plot thickens...

speedo and eco are related so fix the speedo and the other will likley follow. either a lose ground nut on the back of the cluster or the solder needs to be re flowed. if you have the money, just buy a refurbed mother board from bav restorations. or send them your entire cluster. they will return it to brand new condition bulbs and all for approx 240 bucks.

[ckahl2]

Ok, so now this is getting a bit annoying. So my replacement hoses came in and I just put the new ones on. I went to start the car and it wanted to idle at about 1500 RPM. It was steady, however, and seeing that the guy who had the car before me wasn't all that smart, I figured he messed with the adjustment screw on the ICV to get it to idle where he wanted with the bad hoses. I drove it around a bit just to see what had changed and it went pretty well while driving with no hesitation in the pedal or jerkyness (Speedo and econometer cam back on so that seems to be a ground or soldering issue so at least that's solved, thanks for that guys). The issue I had was when I parked it. The car wanted to idle at 1500, maybe up a bit higher now so I reved it a bit out of gear and then the idle wanted to stay above 2000 RPM. I reved once more and then the idle started back up with its bouncing but this time between about 1200-1800 RPM. I let it stay like that for a minute and it didn't die, but the bouncing is still there. Went and checked everything I changed and it all seemed good. So now I'm at a loss. Could it be just that the actual ICM has gone bad? Anything else that would cause this?

I want to thank you guys again for your help, the Jeeps I've had in the past have been super simple so a lot of this work with electronics (especially German ones) is new to me.

[long tall eta]

have you cleaned your throttle body? if it's dirty and the flapper isn't closing that could cause the high idle. also when running unseat the dip stick she should start running ruff also loosen the oil fill cap, same thing, she should run ruff if no difference start looking for vacume leaks.

[ckahl2]

Loosening the oil cap and the dip stick definitely made the car run worse, I also cleaned the throttle body as well as I could, but I still have an odd idle. It now does one of two things, after the car is first started up it just idles high, but after it's been driven and gets up to operating temp. it will occasionally go back to the bouncing idle while I'm stopped. The gas pedal also now seems like it has a bit of a stutter when it gets into the 2-3000 rpm range. It's barely noticeable but definitely there.

[long tall eta]

the fast idle when started may be the cold start injector injecting extra fuel. the maf air sensor is adjustable but shouldn't be done by you if you've never done it before. do you have an enthusiast shop near by? when mine was doing this i took it to guten parts and they did there magic by hooking her up to the what ever you call it that reads rpm's and slightly adjusted everything from the icv to the maf meter. you could also have a bad idle control module.