Strick

I'm working on a 96 LT1 with the auto tranny. It runs fine in open loop, but once warmed up (in closed loop) once in a while it drops into a very rough idle when in gear at a stop. When you put it in neutral, the roughness goes away. No "check engine light" The owner had new spark plugs and wires installed, but 2 wires were crossed. Fixing this really smoothed out the engine, BUT the intermittent rough idle still happens. We ran fuel injector cleaner through the engine, but we still have the same problem. If it was the opti I would expect a check engine light. BTW, the Vette has 60K on the clock. Any ideas? Thanks guys.

pcolt94

It runs richer with no O2 input in open loop which might mask the problem. I would first try to find out (when hot) if it was localized to a cylinder. Like any other engine try pulling off the injector connectors or plug wires one at a time to find the problem.

You might also try to look for a vacuum leak and check out the EGR valve for freedom of movement.

If you had a scanner, I would look at both up stream O2 sensors and the fuel trim numbers.

Strick

Your plan is the same as ours. We're starting with the simple things first. I'm also following Petris" trouble shooting guide. Thanks for the reply. I hate intermittent problems.