Need some quick help with a running issue

[e30Matt]

Figured I'd post it here since it's high traffic and I need help ASAP.

E30's got a running issue, runs great when cold, as soon as it gets up to operating temp the idle creeps up, until eventually it's idling at about 3k. Once this happens, any amount of throttle results in stumbling and misfires on 2-3 cylinders, and a massive cloud of black smoke out of the exhaust. The ignition system and fuel system are all new/verified in working order.

If I pull the fuel pump relay, it'll crank over, run at 3k for a couple seconds, then die. Put the relay back in, no start, keeps flooding itself. If I wait till it cools down, runs fantastic until it heats up again.

Any ideas? I'm scratching my head right now. I know it has a small (read: minor) vacuum leak that causes it to idle funny, but this hasn't popped up until just recently. The car had been parked for about three weeks, and has a full tank of fresh 93.

[e30Matt]

Anyone?

[BenM]

Coolant Temp Sensor?

[der affe]

intake or vac leak is a good place to start..
while the car is running/idling, take Windex and spray it around any place the is a joint or gasket in the intake system. if the rpm raises there is your leak. what about the intake elbow, i recently took mine off and found it was starting to split on the bottom side. i never would have seen it if i didn't take it off.

how about your O2 sensor. how old is it? if it is not metering the fuel correctly that could account for the over rich condition. the car runs rich in start up/ warm up mode, as it comes up to temp the fuel map changes and leans out. an intake leak can be less noticeable when you are running rich for start up, then as it gets to temp, the map changes the intake leak makes it run lean, then the ecu tries to compensate by running richer, which is now way too rich.

last thing is the coolant temp sensor, that helps to control the map by telling the ecu it is up to temp

[Julien]

I'd say let it warm up til it runs like shit than start unplugging shit.
My logic is that when you unplug a sensor it goes into some sort of default mode in the ecu, which should make it run better than it is now.
things to try:
TPS, AFM, 02, (clean your icv with a tooth brush and simple green, works wonders),
Also look for a small vacuum operated solenoid under your intake manifold to see if it has unplugged itself from the throttle body. Last culprite is the vac hose that runs under the intake to the valve cover.

Albiet some of these are just me guessing, but all of the aforementioned are troublespots that to be working properly for an m20 to idle.

HTH
Julien