xkazman

After hours of diagnosing, I hit a dead end. On my 93 SC400 i've I've been experiencing high idle issues. I've since removed the IAC for inspection and reinstalled -- and was fine. I then checked the TPS and sub sensor by removing and replacing with a known good. I also removed / reinstalled the throttle body and and intake also inspected vacuum lines.Now when I go to start the car to set the TPS setting the idle surges up and down violently.

I'm banging my head against the wall at this point. Any help you guys and give, would be appreciated.

oldManTan

surging idle up and down is usually the IACV stuck wide open.

xkazman

Thank you for responding. Funny, this small journey all started with the IACV. I removed and cleaned (wasn't dirty at all). I replaced and still had the high idle issues, so I moved on to the TPS and sub-sensor, I now get the surging up and down. Think it still the IACV? Again it never did this until i removed the TPS and sub-sensor.

oldManTan

cleaning the IACV doesn't do much, they usually need new bearings or to get replaced, i've been having the same issue as well and i ended up just unplugging the IACV when it was working for a moment and reached 850 rpm. try taking apart the iacv all the way, idk if you opened up the casing fully where the stepper is, then twist the magnet so the plunger goes to the fully open position (closest to magnet) then give it one rotation out and assemble it. that should be somewhere around 1200 RPM, then just keep adjusting it until you got the RPMs where you want them. there's not really anything else that could cause surging up and down like that.