My 98 Z71 5 speed with 5.7 won't slow down when I let off the gas pedal. The RPMs will eventually drop down after an extended time (10 to 20 seconds). This has gotten progressively worse over the last few months.
This is only noticed when the truck is moving or when shifting.
With the truck sitting still I can hold the gas pedal down to get the engine up to around 2000 RPMs and the RPMs will drop right back down to around 500 as soon as I let off of the gas pedal.

I would not expect this to make any difference because this only happens when the truck is moving, but the gas and cruise cables are free and the Throttle Body butterfly does not seem to have any obstructions. I wiped the TB down using a rag with some carb cleaner on it.

I found a three year old thread with this problem, but no indication as to the fix for the problem.

Any suggestions would be appreciated?

My 98 Z71 5 speed with 5.7
Any suggestions would be appreciated?

step 1 no carb cleaner. step 2 throttle body cleaner and a tooth brush,,,,remove IAC idle air control....spray into the hole ,,,engine cold let it sit an hour clean the IAC do not try to move it you will damage the gears,,,

step 3 with crc maf cleaner remove maf and follow directions on can and spray the small maf wires...do not touch wires,,,allow time to dry...then install every thing and you will most likely notice the problem is gone ...

step 4 replace PCV and any bad vac lines....10 years is usually when cracks develop or collapse..