Weird idle problem

[crappycoco]

Hi everyone,
so I bought this e30 325is about 10 months back. Its a real fun car, loving it. I bought it from a guy in SF who prepped it for autocross, but kept it road legal - so thats my DD now. Right when I got the car I hurried and found a good mechanic who knows e30's. We did some extensive work on the engine, mostly preemptive, the rest was found along the way. We ended up checking for vacuum leaks, changing the fuel lines, replacing all the belts, tensioners and filters, readjusting the valves, changing the oil, spark plugs, hoses and other smaller engine compartment touch ups.

When I got the car it had a new ICV. I've changed the O2 sensor (original, new) and the AFM (original, 40k miles, virgin). The car is still idling weirdly.

The weird idle looks something like this:
It only occurs when the car is cold (like sitting overnight). You start the car, usually it surges to 1500rpm and settles down to 650-700rpm in 2 seconds. It keeps that idle with no problem. The kicker is when you touch the throttle. The rpm would surge to whatever rpm is appropriate for how much you pressed the pedal, but after you back off the throttle - the rpm will dip under 400rpm, the car almost stalls, all the lights flicker on .. everything stutters for a second .. and then returns back to normal idle. That is, unless you touch the throttle again.

But take the cold car, drive it around the block and park it (still cold i presume), and it stops doing that. I try to minimize this annoying startup procedure by starting the car, waiting a minute at normal idle, pressing the throttle so the car hovers at about 2k rpm for cca 30 seconds. Usually it helps, and the rpm don't dip after I depress the throttle.

I should also mention, that the previous owner installed a "killswitch" at the battery because the car was draining it. I found the fuse (27) but the cause could be a number of things. So im looking into that too. Why am I telling you this? because I think (or at least i thought) the ECU resets if you leave the car without the connected battery overnight. So this week I was driving it with the new AFM and didn't disconnect the battery, to let the ECU learn. Didn't help .. yet. =)


I'm running out of ideas here, does anyone have a clue what could be the problem here?

Thanks guys.

[jlevie]

If the kill switch is disconnecting that battery, that will reset the DME and result in it loosing learned adaption. That aggravates the problem, which is most likely intake leaks. The only certain way of locating intake leaks is a smoke test.

[crappycoco]

Is that in any way related to the vacuum leak test?

[jlevie]

Well in a sense they are the same thing in that they are ways to find intake leaks. The difference is that most vacuum leak tests are limited in where and how large a leak it can find, but a smoke test will find leaks of any size anywhere.

[crappycoco]

ill try the smoke test then =)

[crappycoco]

Car has been smoked, there were two leaks - one on the throttle body, where the power steering hoses connect. Took care of that one right there, waited for an hour and did the test again. One leak revealed itself - the hose that goes to the carbon filter (under the throttle body). I have to take the TB off but I had to order the seal, so I'll do it next week, hope this solves the idle issues.

Btw, I've also removed the ICV and cleaned it. It obviously didn't fix the problem =)

If the leaking hose still doesn't fix the problem I'm guessing the problem is in fuel pressure or in the vicinity.

[crappycoco]

Clamped the hose, fixed some other leaks - smoke tested and there are no more leaks.
One of the "leaking" parts was the ICV too. Turns out the servo inside was shot, and the whole thing wasn't even air tight.

Just got a new one, hooked it up and started the (cold) car. Idled even worse. Took a casual drive. Now the idle seems a bit less erratic, but still not solid.

The car still drops rpm when I press the gas pedal while cold (even with no vacuum leaks, and a working ICV).

I'm out of ideas here. Help?

[Zeckler1234]

My car is having the same problems, took it to an mechanic and he says for me it's the rear main seal? I'm trying to find out if that seal has anything to do with the vacuum system.

[crappycoco]

Rear main seal on what? I need context :D

[Zeckler1234]

Back of motor where the tranny/clutch connect at onto the motor, I think four bolts hold it in place.

[Zeckler1234]

Could also be the oil pan gasket? Idk I'm kind of lost at the moment too, I will post what I find out, I'm just going to pay the mechanic to get it done, 1222 code is to much of a head ache.

[crappycoco]

I made a video of it. This is how its like now, after all the replacements =)
Still not properly resolved imo.

[dnguyen1963]

From your video, it looks like you might have a leaky injector. After you release the gas peddle, the rpm drops then some more gas is injected and the rpm raises again. Just a thought...tee in a fuel pressure gauge and monitor the fuel pressure.

[crappycoco]

Thanks! I've already tried to solve it with the injector fluid product, that you pour into your tank. Didn't really help. I think i'll send my injectors to be rebuilt and see it from there =)

[ak-]

lol 70% of r3v would love to have an idle like yours