weird idle issue.

Hey guys. I'm new to posting here, although I've been lurking for some time now. I have a 1995 318i 5 speed with an m42. It has ~ 188000 miles on it and still runs like a boss.

I have recently encountered a problem though. Every now and again, my car will be ideling right, but all of a sudden drop down real low and then back up and down and up and down and up to the point where it shuts off if I don't give it gas. It'll do this for 5 minutes to an hour. It just depends on how much gas I give it. I usually can rev it up and keep the rpm's high for a bit and let off and it stops.

It's just really aggravating and I'm sick of my car dying at redlights when I'm not paying attention to the tachometer. I know it's not much information, but if there's anyway you guys could help, I'd appreciate it. One of my fellow bmw enthusiasts suggested it was the IAT? IAC? Not real sure what he said. I don't know if this is it, but if it is, maybe you guys could give me some more info.

couple of pics:

Vacuum leak perhaps or maybe a dirty MAF or...?

I was suspicious of a vacuum leak as well, but this problem isn't on an interval basis. It happens at the most random times. You would think a vacuum leak would be constant. Sometimes it won't do it for days. I'm so lost when it comes to german cars lol.

If you don't have any vacuum leaks, my first guess would be a dirty/clogged idle control valve. You can take them apart, clean them, and many times fix the problem that way. Anyway, search "E36 idle control valve" for more info. It's definitely worth checking out and cleaning, just to rule it out if nothing else. Shouldn't take very long. Good luck.

PS: have you ever considered putting the motor from your WS6 into your BMW?

thanks man, I'll try that.

haha no, I wouldn't consider that. I would take it out of another car and do it though. The ws6 is a legit lt1 ws6 manufactured by slp in '96. It was the first year "ws6" was introduced as a package. I believe I'll leave it in the garage and one day have a collectible lol.

Ah, I thought all the WS6s in that body style were LS1s. Anyway, you probably won't have too much trouble fixing the E36. Idle issues tend to be easily fixed on these cars.

yeah, they didn't introduce the LS1 in the f-bodies until this body style:



My body style and that one are both considered 4th generation f-bodies. I believe GM should have called mine a 4th gen and that one a 5th gen, or at least a 4 1/2 gen lol.

Thanks for the icv info. Like I said before, I'm lost when it comes to the german cars.

Hmm, if your issue is indeed related to the idle control valve I'm not sure in your case cleaning it would necessarily do the trick. If you have one that is "completely failing intermittently" I would think it would need to be replaced. When the idle control valve completely gives out you experience symptoms much like you are having. Bad thing is they are awfully expensive, so maybe giving it a clean wouldn't be the worst idea in the world. (The ICV is an run by an electric motor, so if it has an electrical problem, cleaning won't fix that)

The IAT is probably referring to the Intake Air Temperature sensor, which tells the computer the temperature of the air flowing through the intake. I would doubt that is your issue (although I know very little. I'm still a hack mechanic), but it's a $20 part and the labor of getting at it is the same as cleaning/replacing the Idle Control Valve (ICV).

See here for more info: http://www.dvatp.com/bmw/diy/icv_ccv/

I hope that it doesn't need to be replaced. I'm going to clean it tomorrow and pray to God that fixes it. Thank you for your insight.

Yeah they are expensive for what they are ($200-250). That definitely sounds like it could be your issue however. You could always get a used one, but I'm always hesitant to buy used parts unless they are very, very cheap.