Hello Everyone. I've had my 91 z28 a little over 3 years and its been sitting for half a year. I had taken the car to my mechanic but he couldn't find what was going on. The check engine light doesn't come on. So I can't even check it. The car tends to idle really rough. Before it sat it wouldn't switch out of first. It would idle really hard and turn off. Today I aired up the tires and went around the block. It shifted with no problems, but the idling is rough like i said. I don't know what to do. Automatic. Any suggestions?
Okay so while doing a 2nd test drive, it wasn't shifting out of first.

 

Run the car at night. Open the hood in an area with no lights. Look for spark plug wires arcing. If that doesn't turn up anything, pull all the plugs looking for a fouled plug indicating a cylinder not firing. When was the last time the car received cap, rotor, plugs and wires?

 

You can scan for codes even if the CEL isn't on. It's easy enough to check by shorting the ALDL pins and flashing the codes on the CEL.

Did you replace the stale gasoline? Have the injectors ever been cleaned?