mega weird idle rises up if car rolls forward ???

[e30sportchris]

this is driving me mad !!!!
i have a g reg 320 touring the car idles fine around 800 rpm if the car moves the idle rises to 1100 if you stop the car it falls back down to 800
when i say move i mean no one sat in the car and just push it forward 2 or 3 ft involving no throttle action if any one has the answer to this it will be greatly appreciated
i have tried an ecu,air flow meter icv and checked throttle position sensor
thanks

[mrLEE30]

cracks in the inlet pipes, or poor seal in the inlet manifold.

spray some carb cleaner around the inlet side of the engine while it runs, a change in engine speed as you spray is a good indication of an air leak.

[e30sportchris]

ive checked for air leaks already ,it will idle fine all day long stood still if you physically pushed the car 2 ft forward the idle rises by 300 rpm ????
im thinking if its an electric speedo it maybe some how connected to that ??

[Speedtouch]

Does your car have air-conditioning? If so, it may be something to do with that - the ECU has an input that raises the idle when it's switched on.

[e30sportchris]

nah no aircon