Need details. Does the A-frame have to be dropped. Would like detailed procedure before I start

The car will take itself up to 35 without me touching the accelerator. I can rejigger the idle setting by switching from drive to neutral while stopped waiting a few seconds, hearing the engine slow down, and shifting back to drive, it seems to get a new reading, sometimes the same, sometimes slower, sometimes so slow the car clunks out if I am not revving it manually.

I had the computer and the MAF computer replaced by technicians and they gave it back to me saying they have no idea what the problem is. Any ideas?