Need some help here. Got an 03 cruiser with natural asperated non turbo 2.4 thats givin me a fit. It has a serious idle surge problem. On start up it revs to about 2 grand then drops to target idle of 575 or so. After it drops to target idle it surges between 575 and 1800 constantly. If u lightly touch the throttle it jumps up rapidly to almost 2500 rpms and slowly draws down to idle and starts surging all over again. If u turn on the a/c it smooths out the idle a little bit. With a/c on and vehicle in gear it idles perfect for a few min then starts the surge again. Previous shop it was at had timing belt installed 2 teeth off. So I got the joy of tearing it all apart and correcting all that nightmare. New component kit and water pump. Still same problem exists just not as bad. No dtc in the system at all. Checked with both a scanner and ignition cycle system.
vaccum leaks not found anywhere. Fuel pressure dead on target. Pulled upper intake for plug access plugs all good there. Used bore scope to check the valves and piston tops to looked for valve smacking pistons nothing wrong there.
even ran a compression test all cylinders have perfect compression. Cylinder leak down test ran no problems. So I know the valves arnt bent anywhere. Inspected IAC valve was a little cloged up so it got a new one still doin the same thing. So I ask ya What in the world is causing my Idle surge on this darn contraption.
You have a vacuum leak. The fact that when it revs and slowly returns to idle is the key. Look at the big hose from the air filter to the intake of throttle body. Introduction of false air is a killer for running issues.