Rough Idle

Question : OK here we go........2000 Pontiac sunfire gt 2.4 litre engine 180 000 Kmrough idle started suddenly one morning......things ive tried and tested.....changed sparkplugs twicereplaced throttlebody gasketreplaced intake manifold gaskettried new coilschecked engine compression all between 216-222 psichecked engine vacuum not steady but between 14-15" mercuryadded two cans combustion chamber cleanerno check engine soon light!!!my GM mechanic had it for three hours could not find anythingadded one can injector cleanerthing i havent checkedevapegrcatalityc converterfuel pressureengine idles rough only, when it gets above 1500 rpm it dissappears but it takes longer than usual to come back to idle speed , all this happens hot or cold....... Hope you can help or suggest Response to question: Your problem you say is below 1500 rpm and that the vehicle runs fine above 1500 rpm. I would say you need to replace the I A C valve (idle air control). The I A C only functions at or below 1500 rpm. This is a common issue with GM engines. If you have replaced the intake manifold gasket , this should be fairly simple for you. Also when you remove the old I A C clean any excessive carbon that may be present. information from www.freeautomechanic.com