I am looking for answers because the Chevy dealership garage can't figure it out for two weeks now. I see other stories here related to this same topic, so someone has to of found an answer by now. You start the engine, do not touch the accelerator or throttle body. Just start the vehicle, motor runs at 600 rpms, all is good. Move the gear selector to drive the rpm's climb to 1,200 and as much as 1,500 and that is going on level ground or uphill. Put it in neutral, a quick rev and drops back to 600 rpms. Something is telling the throttle body to open just a little from park to drive or park to reverse but back to normal in Neutral or Park.
Who is smarter than Henderson Chevrolet and has the solution?
Nathan

 

Has the throttle body been cleaned of carbon build up at the throttle plate causing it to stick?
If dirty it will stick and the shift into gear is just the system trying to maintain idle under load as it only moves the plate slightly.
Quick rev will move it more and it will snap back to idle position as the rev plate motion is more than just an idle compensation.
If no carbon it just may be a sticky throttle body, then.

 

The throttle body was cleaned maybe 3 years ago. It is original to the vehicle which now has well over 400,000 miles on it. For me it appears to be an electronic issue. Something electronically has to tell the throttle body to open while in Drive or Reverse but then to drop idle when in Park or Neutral. I feel if the throttle body was sticking, it would just stick. I can switch gears from Neutral to Drive ten times. The RPMs will adjust from 600 to 1,200 every time. Very consistent. Nothing sticking. The quick rev is only the release of the transmission torque converter because I have my foot on the break to keep the vehicle from taking off.

 

Could have an issue with your throttle body sticking, like repairman54 said. I'd remove the intake and hose it down with carb.cleaner. Hopefully it's not an ECM issue.

 

We have solved the mystery. Turns out the Torque Converter is bad. Very limited slip now almost stalling the engine. Not sure why that would cause the engine to rev to 1,200 RPM's but that is what the Chevy Dealership came to as a conclusion. So to test this theory, this Tahoe has 4 wheel drive and I am able to switch the Transfer Case into Neutral if it ever needed to be towed. Then checked what the engine would do when the Transmission was shifted to Reverse Neutral and Drive. The engine remained constant 600 RPM's. No change. Because the vehicle Transfer Case is in Neutral, there is no draw of engine power when shifting to any gear. Very interesting, never seen anything like this before but additionally never had any vehicle have a bad Torque Converter.
Nathan

 

I admit I'm no expert on automatic transmissions, like I am with A/C systems, but since the 80's most all torque converters have a lockup feature to increase gas mileage, like a manual transmission. I wonder if that's the/an issue at all? Just a thought.

 

I'll second the convertor lock up is not releasing so PCM increases idle to compensate for the extra ''drag''.
45k mile fluid changes prevent a lot of trans. issues.