DME problems

[bimmer630]

Ive got two dme's, one was in my previous E30 and ran fine in that car but in my new car it has a high idle. It had a dinan chip in it so I took that out and there was still a high idle at times. so i threw in the original to this car dme with the dinan chip in it, and the idle is perfect but i have a code 1222, o2 sensor. it only comes on sometimes, and im gonna change out to another o2 i have, but I probably have two bad DME's, right?


I wish I could make one good outta the two

[jlevie]

Probably not. The root cause of the high idle and 1222 codes is most likely to be from intake leaks. A smoke test of the intake is the only sure way of locating leaks.

[bimmer630]

Nope. Ive checked that. tried a few different
IAC motors, the intake boot is new. remember i get the 1222 code in one ecm and the high idle in the other ecm.

[jlevie]

"checked that" as in a properly run smoke test found no leaks? That is the only way that you can conclusively say that there aren't any intake leaks.

It is possible that there could be a problem with the DME's, but the simpler and more common explanation for the high idle and the 1222 fault is unmetered air entering the intake.

[bimmer630]

You are correct, a smoke test is the best way to check this, and i have access to a machine, but i just never saw the point since one dme has one issue and the other has a completely different issue. I suppose ill stop bein lazy and just run smoke through it, but i dont think ill find a leak

[jlevie]

Since you have access to a smoke machine, plug the exhaust and fit an adaper in the intake boot where the AFM connects then build and hold 2-4psi of smoke pressure in the intake for a few minutes. If there are leaks that will find them.

[bimmer630]

Yeah i did that. no leaks. this high idle is intermittent. the dme is telling the IAC to increase airflow, because if i disconnect the IAC the idle improves. I have tried several IAC motors to no avail. I think the ECM might be getting a faulty TPS signal or maybe its just processing the idle speed wrong

[jlevie]

If the smoke test revealed no leaks, I'm inclined to suspect the DME or TPS. But then the throttle and/or the TPS could be misadjusted. The correct adjustment procedure is to;

1 With the engine at normal operating temperature and slack in the throttle cable, unplug the ICV.
2. Adjust the throttle stop for an idle of 950rpm.
3. Shut off the engine and adjust the TPS so that the idle switch goes to short circuit when the throttle arm is 0.030-0.060" off the stop screw.
4. Reconnect the ICV and the idle should stabilze at 750rpm.

Another possible cause of a high idle is a signal on the A/C pin of the DME when A/C is off.

[bimmer630]

But the problem is only on cold start, so if the tps was faulty, Id have weird high idle all the time.

also I finally charged my AC system and if I turn on my AC the idle screams up to over 2000

[jlevie]

Idle speed should increase with A/C, but not that much. Have you checked the adjustment of the idle stop and TPS? And verified that the idle switch goes to short circuit when it closes?