Engine surging and IAC malfuntion / PVC leakage error ONLY when warm [2003 Civic]
 

Hello everyone. I have a 2003 civic LX. 200,000 miles. I recently (within the last month) replaced all of the valves, the timing belt and components, the head gasket, valve cover gasket, all intake gaskets, PCV valve, and all vacuum hoses except for the brake boost hose (which I tested for leaks with carb cleaner). I also thoroughly cleaned the IACV and intake manifold. My car now starts fine, and idles normally when cold, but as the engine temperature increases so does the idle speed until it finally reaches 2100 RPMs and then starts surging. If I let it surge for about 30 seconds without pressing the gas pedal down (which levels out the surging until released) two error codes appear, IAC system malfunction, and PCV air leakage, and the surging changes from going to 1000 up to 2100 then back down to 1000, and as soon as the error codes appear starts surging more frequently while staying in the 1400 - 1600 RPM range. There is no surging while driving in gear, but as soon as you press the clutch or move it into neutral it restarts surging. Also, while the error code is present there is another problem that has existed since I bought the car that intensifies: When you release the gas pedal entirely or just start to depress it (when in gear), the car shakes violently for a second and then goes back to normal. The shaking does not occur at any other time and the engine brackets seem fine. When the error codes appear the shaking is about 2 - 3 times worse but goes back to normal when the codes are cleared. I don't get why this happens, or even why the error codes appear in the first place with all new vacuum components. I'm also confused as to why this would increase with temperature. I have tried bleeding the air out of my cooling system several times as well and it has not helped. I have checked that all vacuum hoses and sensors are plugged in properly 5 times, and have also tried retightening the IACV and intake manifold twice, and even replaced the PCV valve a second time. If anyone could help me with this (especially with the first problem I mentioned, since I only have 10 days to get my car re-inspected before it becomes illegal to drive) that would be very much appreciated!

Thanks a lot!

Re: Engine surging and IAC malfuntion / PVC leakage error ONLY when warm [2003 Civic]
 

Pull the lid off and look in the throttle body, find the open port (IAC air passage)

With the engine running and surging, use your fingers to block air flow into that open port : Does the RPM drop to normal idle speed or less?

IAC might be stuck in the open position