My dads 2000 gmc 4.8l has a rpm drop while at a steady speed usually 45 or 55 not sure whats causing it, but if wont doesn't seem to do it while using the cruise control any ideas? Any help would be appreciated i really wanna fix this problem for my dad Thanks!!

 

How much does it drop, 400-600rpm? Does it come back up? I assume this is an auto. tranny, maybe it's the clutch engaging and disengaging that gives you about a 400-600rpm change. But if it is the clutch it would do it in cruise control too.

 

yeah about 400-600 then it goes back up but itll keep doing it untill you accelerate even if your foot is on the gas to hold the speed

 

Have you checked out whether TPS and O2 sensor is working properly or not? If they work fine then measure the exhaust back pressure, I think it may be the problem. Excessive exhaust back pressure can drop your engine rpm even if you drive the car at constant speed.

 

hmm we will defiantly look into it thanks ill let you know how it goes