1990 Corvette idling rough?

This car has a fresh tune up with past 6 months (plugs, wires, filters, distributor). When I crank up it starts idling rough to the point of almost shaking. I took it around block and got the speed up and seemed to run better until it came back down to an idle. It doesn’t feel like a spark issue or even a fuel issue. Maybe Air? Any thoughts?

found the problem. It rained and moisture got up into the distributor. Running fine now.

4 Answers

  • The very first step before spending a penny on a rough idle condition is to do a compression test. If the compression is even then you know you have a tune related problem. Without knowing the condition of the engine you could be throwing money at this for days before finally figuring out you have a burnt valve or bad rings in one hole.

    That said, at this point it’s not hard to pull the EGR valve off and block it off to see if that’s leaking and to also disconnect one injector at a time while looking for a no change condition. If you find a low hole you could try swapping injectors to see if the misfire moves with the injector but at the very least do a compression check on that hole before you go to all the trouble.

  • check the computer for error codes. Google search old GM computer testing.

  • Possible vacuum leak, low compression.

  • Air wouldn’t cause a rough idle. What you have sounds like a misfire and even with new plugs and wires, if a piston is damaged and oil is getting past the ringlands that would wet the spark plug and that cylinder would not fire. Have you pulled all the spark plugs to make sure they are dry?

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