97 4.3 stumble on acceleration

[carola]

My truck starts good no matter how cold, idles well but when taking off it seems to stumble. I can't get any speed out of it no matter how much throttle i give it. Once the engine is warmed up it seems to run fine and it picks up speed without a problem. Any ideas out there?

[barbarosa]

Mine did the same thing... Always started, Idled perfectly... yet no acceleration and stumbled under any load (up a hill, etc.).

Turned out to be a partially plugged fuel filter.

[Wheeler88]

Maybe the thermostat is stuck open or not installed.

[carola]

Originally Posted by Wheeler88

Maybe the thermostat is stuck open or not installed.

I changed the fuel filter and the fuel pump is pretty new. The air filter had mice nesting in it and I removed a bale of hay, toilet paper and 5 mice. Still have the same problem though only sometimes. It'll run good for days and suddenly start stumbling about at higher rpm until the engine is up to temperature. The thermostat seems to be working right. I was wondering if the Intake Air Temp switch might be the problem? It almost feels like it is flooding. I also changed the spark plug wires.

[Wheeler88]

Well I would next check the CTS (Coolant Temperature Switch). Check the connection is not loose or corroded. The CTS can be ohmed out to test but I don't know the specs. If you replace it ($9 or so) use some teflon tape or thread sealer so it don't leak.

BTW, Let me try to explain my thought process here, it's the computer in open loop thats hunting for a air/fuel mix (choke) that works well from the input of the CTS. Once operating temp is achieved, via the CTS, the computer goes into a closed loop and monitors additional sensors, primarily from the o2 sensors for proper air fuel mix/ratio. At least thats my understanding, anyone can feel free to correct me. It's how I learn.

[carola]

Originally Posted by Wheeler88

Well I would next check the CTS (Coolant Temperature Switch). Check the connection is not loose or corroded. The CTS can be ohmed out to test but I don't know the specs. If you replace it ($9 or so) use some teflon tape or thread sealer so it don't leak.

BTW, Let me try to explain my thought process here, it's the computer in open loop thats hunting for a air/fuel mix (choke) that works well from the input of the CTS. Once operating temp is achieved, via the CTS, the computer goes into a closed loop and monitors additional sensors, primarily from the o2 sensors for proper air fuel mix/ratio. At least thats my understanding, anyone can feel free to correct me. It's how I learn.

Ok, that makes sense. My next question is where would I find this switch? I'll probably just change it and see if the problem goes away. Are there after market ones or do I have to go through GM for this?
Thanks for the help.

[Wheeler88]

Should be on the front top side of the intake manifold, near the thermostat.