Why does a 1993 GMC pickup engine lope while cruising but starts and accelerates fine?
Had a major tune up Jan 2013, just started problem recently. It starts and idles fine, accelerates fine, but at any rpm 1000 - 3000 in or out of gear it lopes when holding steady engine speed. It is a 1993 GMC 1500 pickup with automatic transmission 2 wheel drive and a 350 engine. The loping is as if it is not firing on all eight cylinders. Exhaust does not indicate carb is running rich, but do smell gas from under hood on occasions.
Check the intake gasket,may have small leak,causing gas to leak,and drawing air in to intake.
I am new to this site so will answer as I see it. The intake gasket may very well be the culprit. I was told one person had similar problems and it turned out to be the distributor cap which had corroded and was arcing causing misfires. Have not checked out either your answer or the distributor as of yet. T_S_T thanks for the suggestion.
My truck is fixed. It was a EGR (exhaust gas recirculation) valve. For all having this type of problem it may or not be the answer. Subvet2