I hava a 89 rs with a lo3.About a month ago I filled up the tank and noticed the tach bouncing a little (enough to go from one side of the line to the other).The idle sounded a little funny so I figured I got bad gas.I got some gas treatment and it went away.Then about a week later it happened again but this time 14 years of crap broke loose in the radiator and blew it.I was ok with that because it makes a nice excuse for a aluminum one!.Again the tach was fine a day or two....then it came back.OK...I replaced the plugs.cap,rotor and fuel filter (basic tune up) on Monday.The car was fine.Today (Saturday) its started again.Im at a loss. Can someone help me with what Im overlooking?
The clues:
*tach bounces
*idle sounds funny(has a "pop" I never noticed before)..occasionally tries to die at a light
*no code shows up
*car drives and responds as good as ever..except when maintaining a speed I feel brief "surges"

 

Stuck EGR valve. If you know what you're doing you can move the plunger while its running and see if it runs better. If you can't move it then take it off and try cleaning it so it moves freely. If its beyond cleaning replace it.

 

Thanx..I'll look into it