Catchy title I know. Here's what I've got.

1992 S10 Tahoe with the 4.3 TBI Automatic.

Truck has always started fine and runs fine at idle or on the highway. The problem I'm having is when I drive through town at 35 or so, the motor starts to miss. I can duplicate the problem in my driveway by putting the truck in park and pressing the gas slightly. The truck goes from a fine idle (around 650 rpm) to acting as if it is choked. The exaust always smell very rich. I've done my homework, and such pointed to replacing the egr valve. Which I did, the problem hasn't gone away. Although the SES light stopped coming on. The computer will not give me any codes, and seafoaming the motor didn't fix it. I noticed if i push the plunger in on the egr valve that i can duplicate the way the motor runs. Here's the interesting thing- If I unplug the vacuum line feeding the egr valve and plug it with a screw, no problems. Drives fine, and no bucking, no nothing. I replaced the map sensor and that piece that connects the vacuum line to the egr valve, still no change. I do have an exhaust leak, by the manifold, but this problem dates to before the leak.

Help-



Second, my transmission consistently acts like it wants to shift. It'll do this in 1st, 2nd, 3rd, and overdrive gears. The problem only occurs when I accelerate. I know the transmission operates off vacuum, could the engine and transmission problens be related? Hard acceleration is fine, no problem if I floor it. But to increase speed a few miles an hour, it will drop to the next gear then come back. Any suggestions???


Thanks for your help!
-Canaan Hackler