93 sierra 5.7 bucking problem

I have a '93 gmc sierra 1500, 5.7 , manual trans and the following problem. When i'm trying to maintain a constant speed and the engine rpm's are around 1500 the engine bucks like crazy. Under a load it's fine. Or if i remove my foot off ther accelerator it's ok. Could it be a vacuum leak? There is 156,000 mi. on her. Replaced the tps to no avail. no check engine light. plugs wires cap all ok. very frustrating.she's making me crazy. any and all input is appreciated. Thanks JR:banghead:

Welcome to AF, kinda of a broad question, many issues can cause this, try cleaning the egr to begin with then you would need to scan it and look at fuel trims and o2 sensor inputs for more diagnostics.

Just because there is no "Check Engine" light does not mean that a code has not been set. We had an Explorer with similar problem and no codes. Used a smoke machine and detected a vaccum leak between the plentum and intake manifold. Just an idea.

Just for information. I resolved the problem. I don't know which fix took care of it but this is what I did.
1) plugs
2) wires
3) cap and rotor
4) new coil
5) egr valve
6) new gasket between throttle body and intake
7) cleaned throttle body
truck runs great now. the only thing is there is a ticking upon acceleration that seems to go away when she warmsup! I can live with this

The distributor cap/rotor is the most common factor for what you're describing.