M42club.com - Home of the BMW E30/E36 318i/iS

DISCUSSION => Engine + Driveline => Topic started by: Jaredmac11 on October 14, 2018, 10:38:51 AM

Title: M42 will not idle once entering closed loop
Post by: Jaredmac11 on October 14, 2018, 10:38:51 AM

E30 M42, completely rebuilt.  New rubber, MUTI removed, refreshed engine completely except for...
crank sensor, cam sensor, coil plugs (COP conversion), IACV, MAF

The engine starts first crank every time and does not have any idle issues until it enters closed loop.  As soon as it enters closed loop, it starts idling rough like it is being choked out and eventually it can fail if I dont keep the throttle on it.

I dont want to start throwing expensive parts at this until I know what it is.  I have 2 idle air control valves in my garage and even purchased a used, working ICV from ebay.  All result in the same issue.  Now Im not going to rule out the ICV but I feel like that isnt the issue unless Im unlucky.

What components should I look at and are there any bench tests I can do?

Edit: tried unplugging the afm. It runs better for a bit then after a minute it's back to a rough idle

Title: Re: M42 will not idle once entering closed loop
Post by: DesktopDave on October 20, 2018, 08:05:14 AM

If it's running rich, I'd test the coolant temp sensor per Bentley. Should have very high resistance cold, and rapidly drop as it warms up. Off the top of my head, you should see about 12K ohm at 32degF, maybe 2500 ohm at 70degF, something like 300 ohm at 180degF (running temp).

Did you clean & test the crank sensor? It won't set any codes, and they tend to fail on occasion. You should see about 1Kohm on pins 1&2, very high resistance on 2&3 and 1&3. Cam sensor is pretty much the same test, although it's half the resistance, like 600ish ohms.

These cars also tend to develop cold solder joints in the DME, those also tend to fail as the coil & injector drivers warm up.