insane rb25 idle problem, diagnose if you dare

[nick-nismo]

So just unplugged the cold start choke valve and the idle air control valve (aac), then started the engine and it still did it, so would that rule them out competely?
Also just tried another z32 maf. No luck. Even with the maf unplugged, same thing.

I guess next is new intake manifold gasket? Maybe a skim of the intake mani?

[amnash]

I wouldn't skim.. but with new gasket give it a good thick coat on each side with spray maker the high temp stuff that's orange from Canadian tire. it will seal for sure. check for vacuum leaks using propane torche(unlit) first though

[nick-nismo]

well i made a boost leak tester as pictured in the OP, and i cant hear or feel really anything leaking, tried spraying soapy water too.
i was thinking maybe taking it down to racing greed, they said they have a smoke tester, might be more accurate than looking for bubbles especial underneath the intake mani where its hard to get to.

[amnash]

ya that's worth a try. my rb20 did this exact thing when I built it but both my cams where out a couple teeth because I was an idiot about it lol. you said you had nistune? they're a tuner around that could have a look?

[nick-nismo]

ya the guys at RG im sure can figure it out i just dont have funds for shop time right now ya know.

[h4X6]

Did you check yo make sure your cams are proper. Ei: not a couple teeth off

Sent from my Nexus 4 using Tapatalk HD

[nick-nismo]

Yup did that yesterday

[h4X6]

Yup did that yesterday

Well I'm out of ideas... Lol if it idles funny and runs perfect then I'm done Lol

PS. Buy my turbo!! Lol

Sent from my Nexus 4 using Tapatalk HD

[nick-nismo]

hmm i think im getting somewhere here,
the new TPS that i bought from nissan, the part number is A22-646 J01 and no matter what position i rotate it into the idle is jumping up and down, as per the video.

so i threw in the old one, part number is A22-645 J00, and at anything above .55v the idle is stable but high ( around 1800 - 2000)
and at the normal 0.45 - 0.5v the idle is not stable.

so tomorrow im going to try and order a brand new one with the same part number as the original one. (A22-645 J00)



and i still havn't heard back from my friend ill txt him today though!

[amnash]

just check the voltage on both of them, car doesnt even need to be running. just open throttle by hand slowly and watch with multimeter to make sure it goes up smoothly. set for lower voltage then open all the way to see if its within spec and again check for nice smooth voltage change on the way up

[fwd suck]

do you have cams? head port/ polish? maybe you making boost at idol. sending air back thru the turbo and maf, messing up air fuel ratio. it happened to my gtr. map the way to go.

[nick-nismo]

so i swapped in another stock rb20 ecu and the car ran fine and i called racing greed and they thing something inside my ecu broke. but does that even make sense because the car drives fine just only at idle its messed?

[Skym]

It could be that AACV is adjusted higher than what ECU is adjusted at (both should be at around 650rpm). ECU could be bringing rpm down and AACV could be raising it again (with help from o2 sensor running engine lean, rich).

The diagnostic screw on side of ECU can adjust idle rpm in small increments (turn screw to far left to get into idle rpm adjustment mode, unplug AACV and adjust AACV screw to correct position for 650rpm, plug AACV back in and see if idle rpm stays the same, if doesn't, repeat, then I think was return screw to run position via turning screw to right. But if adjust screw to the right with AACV plugged in, I think rpm should increase a small amount at a time) and is known to fail (keeps turning, always count amount of turns of screw when adjusting). Might be worth checking that diagnostic screw is in run position.

[nick-nismo]

is this in run position

or is it supposed to be between the 2 lines on the top. ?

[Skym]

I think it was inbetween the two lines (looks like it's currently in diagnostic mode). I had mine sitting on the left border of two lines and when hit bump in road, cat light on dash would flash (acts as a engine check light, cat overheat light).