My Evo 9 with ~129,000 miles has a rebuilt engine (stroked to 2.4l), stock everything else, with around 28,000 miles on the engine. The engine has new valves/guides/seals with the rebuild but stock springs (or at least I didn't change them personally). I had a machine shop install the new valvetrain components.

About a year ago I started to hear a clicking-type sound from (I believe) the engine. It only comes on briefly at low RPMs (lower being 2-4000rpm and briefly being 5-10 clicks over 1 or 2 seconds and then goes away), usually if I load the engine at low rpms. Never happens while just cruising, idle, or at higher (5000+) RPM at any load.

My first thought was lifters but I can't imagine why lifters would only tick briefly when I press the gas pedal. My second thought was injectors as it happened briefly at times (not all times, however) when I pressed the gas pedal. Perhaps they're becoming old and the higher load from the bigger engine is pushing them too much. But it also will occasionally, and more often lately, do it briefly right after I let off the gas pedal and decelerate.So if it's doing it when there is no fuel injection maybe it's not the injectors.

My last thought it possible the mivec system. I want to "turn off" the mivec system to see if it still does it but I'm currently having issues withe reading/writing to the ECU so cannot do that yet.

It also sometimes happens when I start the car but if I have the car started I can't hear it from the engine bay.

I know you can't logic your way out of car problems - does anyone what idea I might be able to start checking to figure it out?

 

The IACV clicks when it's working quickly, but that's a normal noise. Listen just under your throttle body next time your idle is acting erratically.

 

I've heard the IACV clicking before and, at the very least, it isn't a normal IACV clicking. Anything you can suggest for checking the IACV out? I don't really have idle issues.