Wierd 99.5 1.8t A/C unit- revving issue

[iwt5007]

I have had a problem with my a/c unit in my car for the past month now. It started when i was just driving with the a/c unit on, when suddenly it went out and shut off...i tired repatedly to turn it back on and there was no response. As this happen i noticed while driving, that my car was reving at low rpms...somewhere around from 800 revving to 1200, at every stop light i could feel and hear the revs and as i progressed into higher speeds and gears, it felt as if the pedal was being pushed down on its own, i also noticed that everytime it revved, the back lights faintly went on in the a/c unit for the duration of the rev......i decided to take my car to a local vw/audi shop and they started by cleaning the fuel injectors and throttle body.... they also diagnosed that my a/c unit needed to be repaired....300$ later i got my car back with no a/c unit in the dash but the revving had stopped...I drove around for the next 2-3 weeks with no a/c unit but no revving....turned out that the company that my local shop had sent the a/c unit for repair to, couldnt find anything wrong with it, they sent it back and now my shop thinks i need a new unit....they put the old unit back in and its still doesnt work as expected.....but now the revving has come back and i noticed it as soon as i left their lot.....I'm thinking that their is some relationship between the a/c unit and the revving but what could it possibly be? I'm not tryin to buy a new unit if it is something else that needs to be replaced.

[offroader1006]

well here's the thing.

our ECU is told by the A/C panel when the compressor is turned on, and compensates by activating the motor in the throttle housing to raise the idle to accomodate for the increased engine load. If your ECU thinks the compressor is activated, and it isn't, your idle won't be steady.

you can check terminal C12 on the A/C panel(the signal wire to the ECM) when you cut the A/C on, and see if you get a voltage change(indicating communication). if nothing, you probably have a internal fault in the panel. If it does change, you may have a broken wire under your dash, or high resistance on a connector terminal.