03 envoy rpm issue

I have a 2003 GMC Envoy I6 4.2L. When driving above 50 after vehicle has warmed up it will drop rpm’s by 300-500 and they go back up. This happens for several minutes at a time. It did it for over 20 minutes last night while driving home. I thoroughly cleaned the throttle body this morning (removed to clean) because in my researching for the solution it seemed that was the answer. Also left battery disconnected the entire time to allow computer to reset itself for clean TB. Took it for test drive and after about 10 minutes of driving it started doing the same thing. Took it to autozone to see if maybe they could pull a code even though there is no SEL on at the moment, but nothing came up. I am dreading if it’s in drivetrain, i have only had the vehicle for about a week and a half. Bought it used from a private seller and it drove home fine the day i bought it and a couple days after, but now it’s gotten worse than when it first started. Please help!

Rather than the throttle body, I would suspect the Mass Airflow Sensor (MAF) to be the culprit.
Get some MAF cleaner at the auto parts store, remove the MAF, spray it with cleaner, allow it to dry, and reinstall it. With any luck, the symptoms will be gone.

+1 to VDC’s post.

It’s my understanding that there is not a MAF sensor on the I6 4.2 engine.

When the rpm’s drop, does the engine still seem to be running well, the problem is just that the speed dropped while you kept the accelerator pedal in the same location?

hmm… if the engine still seems to be running ok, and you’ve verified the throttle body is clean and unobstructed, my guess is there’s something occasionally loading down the engine. First guesses would be something on the drive belt system, like the AC compressor, power steering pump, radiator fan clutch, possibly the water pump, something locking up when it shouldn’t be. My guess for the places to look first: AC compressor or fan clutch.

This could be something inside the engine, but unlikely to be a drive train component, unless perhaps the brakes are locking up for some reason.

Could this be shifting in and out of overdrive…or it’s highest gear.

Have you checked the tranny fluid to see if it’s burnt or smells.
Should be a Deep red to pink if you wipe some from the dipstick onto a paper towel.