I have a 1993 toyota pu, v6 manual, 3.0l vze engine, engine is running rough, after engine warms up, I push in the clutch to change gears and the tach goes down to 500 rpms, and the engine is struggling to stay running, but if I tap on the gas petal, the rpms goes up then back to normal, around 1,000 rpms. Engine runs smooth then. But there are time the engine runs a little rough even when rpms are normal,recently I had the gas damper replaced. What could be going on? thanks-Lee