RB20DET Lumpy Idle

[osamathefreak]

Hey guys,

I've been searching everywhere for weeks and ive found things similar to my problem and tried the appropriate fixes suggested and cant seem to fix it.

Ive got a R32 RB20DET, the engine is 2nd hand to replace a RB20DE+T i accidently bought with the car and blew up within hours. The car starts fine 3sec or so but has an really lumpy idle almost sounds like a subaru, when driving it sounds the same, heres where it gets different.. after 2.5-3k RPM its sounds great! Turbo winds up and she goes like a cut cat. its only lumpy idling and runs fine at high rpm and under boost. Ive done replaced spark plugs, changed coil packs, changed ECU and reset with known Working, check fuel lines and pump, changed oil and water system, checked crank angle sensor. almost everything i can think of ive changed out with known good new or checked.

PLEASE HELP!! So lost for ideas!!

[Ozzie]

Have you tried cleaning/replacing the air flow meter?
Also make sure the contacts for the AFM plug are in good condition, and not corroded.

[osamathefreak]

Ive tried cleaning it no difference and the contacts look fine on. Its the one from my old running engine. Thanks

[Ozzie]

Does the temp go up really high?
White smoke/steam from the exhaust?
I'm wondering if you may have blown the head gasket, and once the engine gets to 3k revs, it has enough pressure to push the coolant back out of the bores?

Maybe start it up, and let it run with it's lumpy idle for 30 seconds or so (with the radiator cap off)
See if you are getting air bubbles forced out of the radiator.
After the 30 seconds, turn the engine off, and remove the plugs to see if any water/coolant is present on the plug tips.

I hope we can figure out your problem. Let me know how this goes.

[osamathefreak]

the temp is slightly higher than my old engine but ive changed to a 25det alloy radiator and i think its blocked around %40, it blows white when its cold but not when its warm, im hoping its not a headgasket. Im thinking might be a exhaust manifold leak, when i tried to tighten the bolts the 3 of the studs came out (snapped), does this match the symptoms? thanks for the help

[Ozzie]

Maybe start it up, and let it run with it's lumpy idle for 30 seconds or so (with the radiator cap off)
See if you are getting air bubbles forced out of the radiator.
After the 30 seconds, turn the engine off, and remove the plugs to see if any water/coolant is present on the plug tips.

Do this first, just to (hopefully) rule out a blown head gasket.
Also, get a replacement radiator asap, if you believe it's blocked about 40%. The RB20DET doesn't like excess heat at all.

Is your idle like this?
[youtube]http://www.youtube.com/watch?v=KpFZZH3PBi8[/youtube]

If so, check your IAC (Idle air control) valve too.