Puzzling M42 Engine Light Issue

[WineCountryE30]

1991 318i with a M42 and a Getrag 240 5 spd w/318k miles. (Purchased at 3k miles)

The other day my check engine light came on while at idle, sitting at a red light. It was idling fine but of course I decided pulled over to take a look. As I gave it some gas the light disappeared. I pulled into a parking lot and did a quick survey. The temp was cool, the engine sounded fine, and the exhaust was not sweet smelling. I started it back up and had no warning lights. A day later the light came back on again at idle and again disappeared when I gave it some gas to get off the road. After a few more occurrences I have found that the light only comes on below 1.75k RPM and disappears above that. It only does this occasionally, and there is no noticeable difference in the way the car is running when the light comes on. It doesn't run hot, sputter, die, smoke, or make any noises. I am at a loss here. I don’t have a way to check the codes short of taking her into the mechanic, which I try not to do because I like to do all the work myself. I love my E30 and any advice would be welcome.

[The White Guy]

Idle controller? O2 sensor? How clean is your air filter?
Codes can tell you allot. It might be worth it to see if you can get the codes read from an independent BMW Mechanic for cheap or from Advance auto parts if they can read them.
Then fix it yourself.
Stan

[Dj Buttchug]

intermittent CEL like this is almost always lambda control code 1222. You can fix it with a new O2 sensor but sometimes the problem is elsewhere. It is often a mystery that can be a real pita. The performance of the car will likely be unaffected by this code, that is, if it is in fact 1222
GL OP

[djmossm42]

My car has the exact same issue, I've done most of the obvious things, O2 sensor , cleared all vaccum leaks. The code is the dreaded 1222. You can do the stomp rest to pull your codes. I suspect it is the idle control valve because every now and then my idle will creep up above 1k. Also suspect, the flap spring inside the AFM may need recalibration. There is a YouTube video showing how to do it on an E36 318ti. Also got a set of reconditioned injectors that I will be installing soon. Based on the 1222 code description it's a lean code. My logic tells me it's not getting enough air and/or fuel. After those items I dont know what else could cause this.

Sent from my SGH-T769