I have a problem that is getting worse - my 1985 V6 GT manual with 130,000 miles on it has a hesitation and stumbling in all gears around the 2000-2300 RPM range. Even in neutral, if I rev the engine to around 2000, it starts to stumble and hesitate. There is sometimes a loud buzzing noise from the engine in this RPM range, but it goes away when engine revs higher or lower. It is freaky in traffic because it feels like the clutch is slipping in and out even though it's not! The car lurches forward and back like it is not getting enough fuel, or timing is off. It starts fine, has great acceleration otherwise, and runs great except in that one RPM range. I just replaced the coil, rear spark plugs, and wires about a year ago, and the front spark plug wires, plugs, cap and rotor 3 days ago along with a new O2 sensor and EGR valve. Could it be the throttle position sensor? Coil? Or.....??? Thank you for any advice.

The Throttle Position Sensor may have a bad spot that would show up at the same RPM no matter what gear you are in. There is a test for it around here somewhere......

OK. this will help. http://www.gmtuners.com/tech/TPS_IAC.htm

[This message has been edited by Gall757 (edited 03-26-2014).]