1991 S-10 - Rough running when warm

Did you check your thermostat or your fuel pump?

I have not tried checking the thermostat or fuel pump. The rough running will happen almost immediately. If I start the engine and drive 100 ft, then turn it off and restart, it will then run rough. I did not think the thermostat could be the culprit because it really does not have to be run log for the problem to occur. I will, however, check the fuel pump.

Thank you for your suggestion.

--Mike

Did that work?

Acually the answer is as follows. Although you are not supposed to unplug electonics while the engine is running, I did. I was driving the other afternoon and the engine ran perfect to my destination, only about 5 miles, but immediately after a restart, begin to hesitate on deceleration. I pulled over in a parking lot and started unplugging sensors, one at a time, and driving around the lot like a crazy person until I found the culprit. As soon as I unplugged the sensor to the EGR control, the engine ran as smooth as the day it rolled off of the showroom floor. The EGR valve is not closing fast enough on deceleration. It needs to snap shut like a throttle. As for why it runs OK on first start of the day. The computer ignores a few sensors on cold start because they are so out of range, I am guessing the EGR valve is one that is disabled.

Thanks for your input.

--Mike

Ok. What did you unplug egr because I have a buick that seems to have the same problem so maybe I could check it out. It was a sensor, valve or selenoid?

On my S10 I found the EGR valve and followed the vacuum line back to where it connected into a one inch by one inch black plastic block attached to the side of my air cleaner. This had one vacuum line coming out of it that came up from the base of the carb/thottle body. This is the vacuum feed. It also had a plug of wires in the opposite side. I disconnected the wire plug. This stopped the vacuum from being applied to the EGR but did not cause any leaks. When I did this it ran perfectly smooth.

Hope that helps.

P.S. I replaced the EGR valve yesterday and except for one of the bolts not wanting to come out, it went pretty smoth and now it runs great.

I think we have other issues now because it goes, but only if you push the gas ever so lightly because as soon as you push with any pressure it stalls. Also, while the car is running the is no flow from the hose to the thermostat to the radiator.
Buick lesabre 1993

I have worked on various cars over the years and I am getting pretty good at diagnosing my 1991 Chevy S10. As much as I would like to help, I am not a full time mechanic. I think it would be best if you would post your Buick questions in the Buick forum where another Buick owner or mechanic can help you.

--Mike