So my 95 trans am runs great when it’s cold but warmed up it barely runs. I’ve been trying to figure this out for the past two years. I did the parts cannon and replaced everything I could think of the would cause it and it still does it. So I checked the 5v reference from the ecu to the coolant temp sensor and its reading only 3.5v so I’m guessing that has to be it. My question is my ecu crap or is there a y I can use a 12v to 5v step down to create a 5v reference. I have no body around here that will touch a OBD1 car. And no I don’t want to convert it to X24. It’s a Comp T/A and I used all NOS parts on it.

 

Did you measure the reference voltage with the connector off the sensor?

Check reference voltage at the throttle position sensor. They share the same PCM ground. If you have an auto trans, the trans fluid temp sensor also shares that ground.

The PCM reference voltage regulation can go bad - had a case recently. But it’s rare.

 

The TPS showed 4.5v at the sensor. But 3.5v at the CTS but the wire and plug is good. But I check them about a year apart. This has been a 2 to 3 year thing.

 

What was the resistance measured between the sensor and the PCM on the wiring?

 

I don’t remember anymore it’s been awhile since I looked at it. I’ll check next time I’m where my car is.

 

When you threw parts at this was the egr valve one of them?

 

Yes it was one of the first. And we did two Optisparks and coolants temp sensors.

 

What about the pre-cat O2 sensors? They can cause problems when the engine warms up and the PCM enters closed loop? Assuming the PCM is getting a correct coolant temp, and the O2 sensors are heating up, the transition to closed loop occurs at ~206 seconds after cold start.

Might be time to run a data log to take a look at what all the sensors are reporting, and how the readings change as the engine warms up.