Questions and Answers

Chevrolet K1500 Decel Bucking Q. Hi there, I need some help. First, it's a 1991 Chevrolet K1500 Silverado with a 350. Fully loaded: A/C, P/S, P/l, P/B, P/W, automatic transmission, EFI, and 235,000 kilometers (146,022 miles). The truck also has slightly oversized tires which sets the speedometer out by 11% (don't know if that's important or not?)

The problem:
Highway speeds, in overdrive, going over 105 kph (so actual speed is +/- 110 - 112 kph, (65 mph) no problems). Slow down to less then 100 kph, and the truck starts to run rough, cough and sputter. If I shift the transmission into drive while it's doing this, the problem stops. It seems as though when the rpm's are up, no problem, rpm low, problem? It does not doe this when the engine is cold, only after the engine has been running for more then 60 kilometers or so. Any ideas you may have would be appreciated.

Sincerely,
Terry

A. A couple of things come to mind. A bad EGR valve could do this or should I say a problem in the EGR system. A problem in the torque convertor clutch could cause this too. I saw a truck that had a intermittent short in the TCC solenoid that when applied would spike the ECM and take out other systems sharing the same quad driver inside the ECM. You could rule this out by unplugging the connector on the transmission and drive it. As for the EGR, same thing. Pull the vacuum hose off the valve and plug it with a golf tee and drive it.