I'm trying to track down a cold (as in the engine has been sitting for >8 hours, not outside temps) stumbling problem at low rpms, and I've determined that it only happens in open loop. After the car warms up for about 5mins and the idle lowers it runs fine, the problem is gone. I'm getting no trouble codes and the car has fresh plugs, wires, cap, and coil. Does anyone know what sensors to check?

 

it's normal. your car probably doesn't like to run too rich

the ECU reads every sensor except the O2 sensor in open
loop, the O2 sensor must be at ~600F to function properly.

Additionally, during open loop, the timing tables and other
such values have been hard coded, and it runs off of them
to keep the car going. open loop runs much more rich.

If you're not getting codes, I would say your car is
running fine and all the sensors are working, it just doesn't
like to idle very rich. (which is what open loop is, a rich idle)

 

Well, that would be fine if it was running rich but I think its running lean. When it is stumbling real bad I can sometimes hear it popping thru the intake.

 

I think there's a sensor on the intake that controls the cold-start injector. It's a type of temperature sensor.

Maybe that's bad?

I would also try doing a real heavy duty carbon cleaning.

You have to get the stuff that the dealerships use.

The only place I know where to get it is from some dude that owns the Fiero Factory in Alabama.

He sells you a kit with 3 cans. Two go into the fuel, and one is sprayed into the intake. It's heavy duty detergenty type stuff. You put it in on a quarter tank. It COMPLETELY cleans your pistons, and cyl chambers and intake valves... everything.


www.thefierofactory.com

or fierofactory@juno.com