bad idle when warm - MAF?

[e30_kid89]

my motor's in exhuast done, every sensor is there and it is running i noticed when the car is cold the idle is pefect - right on where it should be BUT as it get warmer the idle starts bobbing up and down anywhere from dangerously low rpms to 1500 - 2000 rpms...when it reaches a certain warmth it just stalls. when i plug the maf out the car still had the bad idle but the car will keep on running.also when i rev the motor over 3K and after let go with the maf plugged in this is what happens:

-car idles like it whats to stall
-CEL comes off briefly and then back on
-then idle goes back to being smooth or bouncy when warm

seeing how all the motor's behavours change either with the maf in or out could it be the maf that is not working?

Devon.V

[Brew]

My guess is O2 sensor. Try disconnecting it to see if your problem goes away.

[e30_kid89]

still the same with or with out the o2. could it be a vaccum leak? i would be suprised if it is because when cold the idle is perfect.

[PeaveyBassist]

Check what code the DME is throwing.

Will

[Skafrog]

Had the same problem a while back. Changed the ICV, and problem was gone.
Unplug the ICV, and see what it does. It should flip out.

[Mike B.]

I had the same symptoms, take a look at this thread - http://www.r3vlimited.com/board/show...ight=O2+Sensor

[e30_kid89]

mike my friend u've just gave me a real swift kick in the right direction. my green wire on the o2 relay is gettin 0V @ all times and the brown/green is always getting 12V..i temeporarily jumped it just to see what happens when the motor is warm and it was acting strangely but no longer stalling when warm......looks like i have to go through the fusible link route and cut back into all my x20 - c101 wiring to get to the green/violet wires:(

just when you think you're done with wiring............

[e30_kid89]

well i've isolated the fuel pump relay and used a fusible link to fuse #11...i havent driven the car so the DME cannot i guess adjust so im going to unplug the battery and let the DME reset itself.

lets see what happens...........

[e30_kid89]

tried it, not working and the brown/green wire for the o2 relay still has 12V, green 0 at all times. help???

[02stu]

First, check your crankcase breather valve. If this is not working your car will not idle when its warm. If you remove the hose you should feel or see air moving out of it.

Second, check for unmetered air coming into the plenum and around the throttle body, I think your running lean. Leaks that are letting unmetered air in will show up more when the engine is at operating temperature.

Third, I doubt its your 02 sensor, m50s can run relatively smoothly on open loop w/ no 02 sensor at all. I don't have an 02 sensor and it runs fine, the gas milage sucks though. My bet is its your maf meter.

Like I said before I think your car is running to lean, your RPMs dropping low to a rough idle after revering the engine is a tell tale sign of this, if you were to rich your rpm would not want to return to idle. If your 02 sensor is not working properly your car will defalt to open loop and run rich so I don't think your 02 sensor is the source for your idle problem. The reason why you don't experience the problem when your engine was cold was because your ecu is richening your mixture to "choke" your engine. If I were you I would try to find someone in the area that would lend you a MAF meter to see if that fixes the problem.

[Mike B.]

Mine didn't get better right away either. It took about a week of driving before I saw significant improvements. I really have no idea on why the fix worked, but it did.

[adrock1]

couple more ideas have you checked your fuel pressure? and check the hose going to the fuel pressure regulator(the vaccuum hose). there is also a plastic plug on the bottom of the intake manifold were the fuel pressure regulator hose plugs into you can actually remove this plug and there is a rubber o-ring inside i've seen these go bad. the cars that had this problem had eratic idle problems that seemed like icv valves.

hope this helps

[e30_kid89]

i must admit 02stu that the car when i rev it is running very noticably lean.....so a vac leak couldnt be too far outta the question....also when the idle goes haywire i can hear the intake sucking very louldy...i dunno if that means anything but might as well note it.

[e30_kid89]

update time, sorta:

well i bought a brand new o2 and installed it, the m50 has been running more smoothly but when it gets warm the idle is sitll surging +/- 500-1000 rpms, which sadly is an improvement. CEL is still on BUT when i give it a lot of gas the CEL turns off but then the car stalls when i let off the gas. also during the start up the CEL is off but the initial start up is rough. this is about 8 seconds after the motor has turned over. after the idle smoothes out CEL comes back on. i cant retrive the codes with the stomp test. ive tried a zillion times. my diag. port is working and if i had a code reader tool i would be able to retrive the code(s)

anybody know what this could be? please guys besides this issue the motor is running great.

[adrock1]

assuming you've checked everything. have you tried another MAF.