Rough start/poor idle on cold start

[gk35]

'94 Bonneville, 228 K miles.

Recently, I've had intermittent problems with a real poor idle on a cold start. I have to keep the RPM above 1000 to prevent a stall. Idle resumes normal working conditions once the engine has reached operating temp. No CEL.

I checked the ignition control module following the excellent diagnostic guide found at https://troubleshootmyvehicle.com/gm/3. ... ondition-1
All is well with the CPS and spark plugs. I noticed a low voltage read from the alternator, and the auto shop confirmed it failed testing. So I replaced it, along with the idle control motor. Cleaned the MAF and throttle body.

But still having the rough start/poor idle when engine is cold. Any thoughts?

[imidazol97]

I would suspect the coolant temperature sensor is not giving the right reading to the computer.
If it's saying the engine is warmer than it really is, the computer will not be feeding enough
gasoline for the cold temp of the engine--essentially not giving enough choke to enrich the
mixture in the old days of carburetors.

Is this a car that can be read by today's common diagnostics or did that start in 95???

You need to get a diagnostic unit that can read it when the car is cold overnight and see
what the temperature is that the coolant temp sensor is giving to the computer.

[96 SSEi]

I would first unplug the MAF sensor located on top of throttle body - it has abc on it.

just unplug that sensor and see how she starts and idles - if it returns to normal, you leave it unplugged and keep rpm under 3000 if you drive.

you can clean it if indeed its the source of the issue.