Help! Warm start issue...

[goinstrong]

My M42 starts and runs perfectly when cold. If I go to restart it after about 20-30 minutes, it runs super rich until the computer figures out the car is warm. I can turn it off and restart it, and then it runs fine. I replaced the coolant temp sensor, and it helped for about 6 starts, and now I am back in the same situation.

The engine is in an E21, but the PO of the engine told me this was an issue he had when it was in his E30. Could it be the ECU? Any other ideas? I use it to run errands on the weekends, and it gets a little annoying. Other than that, it is a blast! Thanks for any insight...

Tim

[bmwman91]

I assume that you swapped the M42 harness in?

Chances are that this is a super easy 5 second fix. Up on the main loom that runs along the firewall (on the E30 anyway) there is a single wire with a connector plug. This should NOT be connected on cars with O2 sensors, which is all US models. See if that connector is connected and disconnect it if it is.

[goinstrong]

bmwman91,

Thanks for the tip! I will check this and report back. You assumed correctly that the E30 harness was swapped in...
The harness has been wrapped all together. What color is that single wire I am looking for? Thanks again.

Tim

[bmwman91]

See image on bottom left.

[goinstrong]

It worked! Okay, it took me 15 seconds, but it starts properly when it has sat for 15-25 minutes. There was one wire on the harness that was obvious to disconnect.
THANK YOU!!

Tim

[bmwman91]

Glad it worked. A LOT of people see this little connector disconnected and assume that it should be connected, and then spend a long time trying to figure out why their car won't run.