I could really use some help and/or a sanity check with my 2004 EP3 Civic SiR (Canadian spec) with the stock K20A3 (aside from a cold air intake from a previous owner).
I've been getting the P0507 code ("the engine's Idle Air Control system is producing a higher RPM than the target idle speed") and the engine is continually surging/rev hunting between 1000-2000 RPM at idle. After a bunch of searching, I found that the common culprit is typically the Idle Air Control Valve, which just needs cleaning. So I cleaned it, and problem solved! ...for a couple months before the issue returned. Since then, in rough order I have:
- Replaced the intake manifold gasket, throttle body gasket, idle air control valve gasket, and PCV valve.
- Followed the idle relearn procedure.
- Conducted a smoke test (smoking into the intake to look for leakage and smoking around the exterior of the intake manifold and connectors looking for signs of suction) and sprayed an accelerant around every conceivable joint and crack of the intake manifold (to see if it affected the RPM). No conclusive results.
- Replaced the idle air control valve
- Car started producing error P2279 ("Intake Air System Leak")
- Replaced the throttle body with a second, used one (plus a new throttle body gasket)
- Burped the coolant lines
- Followed the idle relearn procedure.
- Replaced the throttle position sensor
- Replaced the throttle body with new one
- Replaced the air intake temperature sensor, manifold pressure sensor, throttle position sensor, and vapor canister purge valve
- Followed the idle relearn procedure.
The problem persists along with both the error codes (P0507 + P2279) and I'm at a loss for what to try next. What am I missing? All the lines and hoses I've inspected seem to be in good condition and the smoke tests didn't reveal any leaks. I unplug my battery for a day or so to reset the ECU and then make sure the battery is well charged when I start/test the car. My best guess is that maybe the new intake manifold gasket is defective, but I'd like to avoid needlessly removing the entire intake manifold again.
Thoughts?