insane rb25 idle problem, diagnose if you dare

[nick-nismo]

so i was trying to figure out this problem with skym over pm but i still haven't had any luck so i figured i would post this here so maybe if others get the same problem this will help resolve any issues.

so far what ive done is.
1.) brand new TPS from nissan set at .45v and .5v no luck.
2.)cleaned aacv and air regulator.
3.)aac plugged in and unplugged the issue is erratic, some times the car will idle fine and then others it will idle horribly (ive attached a video of whats going on)
4.) changed o2 sensor, and run engine with it unplugged.
5.) ran engine with maf unplugged, no dice
6.)i pressurized the whole system up to 20psi and fixed a couple small leaks, (except for a really small leak between intake manifold and head, tightening the bolts made it almost nonexistent)

i bought a new aacv off a member so when that gets here ill try that and post the results. if that doesn't fix it i think im going to have to pull the intake manifold off get a new gasket and possibly skim the intake manifold true.

or could anything else be the culprit, bad MAF or ecu maybe, or maybs timing belt skiped a tooth.

[amnash]

you have timing belt off? double check cam timing. only take a second to check

[RABBIT]

what are you using for EMG?

[nick-nismo]

i'd have to reset my timing if i inspect the belt, dont quite want to do that yet.
and car is using rb20 ecu with nistune. ran perfectly fine for around 2 months.

[nick-nismo]

well swapped in the new accv that i bought from a member here and still no dice its doing the same thing. i doubt the sensor is bad, said it was working on his car.
checked ecu for codes, 55 all good

im fully out of ideas now

[amnash]

check your timing belt... it takes two seconds to remove upper cam gear cover(5 bolts i think) and then turn crank with ratchet until #1 is at TDC.

you need 23mm socket for crank pulley bolt.

edit: and if the timing marks are bang on then just put the cam gear cover back on and your done.

[nick-nismo]

yeah i just did that!
honestly i was kinda hoping that it had skipped a tooth so i could fix this problem but everything was perfect. crank at tdc and cams were both in correct position.

[Skym]

This is on a rebuilt engine???

If so, did you degree your cams with a degree wheel, etc, as skimming block, head can retard the cam timing -

http://www.kelford.co.nz/sole-purpose-of-degreeing-your-cam

[nick-nismo]

no stock long block, s1 rb25

[Skym]

Are you sure it's stock (sometimes engines are refreshed in Japan)??? Doesn't harm to double check it with degree wheel, etc to rule it out.

I think have ruled out sensors, so has to be mechanical (camtiming, etc).

Camtiming can make idle rough (the VVT part is known to fail and sometimes error code doesn't pop up on ECU with sensors, had that happen with TPS), look under "making a good use of VVT" -

http://www.tomei-p.co.jp/_2003web-catalogue/e064-065_camshaft.html

VVT works at 1050-4500 for R33 RB25DET -

http://www.tomei-p.co.jp/_2003web-catalogue/e090_camshaft-specs.html

[amnash]

couple other shots in the dark, doesnt hurt to pull the plugs and have a look. then with it running in the state it is unplug ingnition coils one at a time just for curiosity sakes(might find something weird) and if possible find someone local and swap in another ecu

[nick-nismo]

im like 80 percent sure its not rebuilt, just a low km motor.
actually funny enough since I'm using the rb20 ecu and harness i have nothing for the VCT. solenoid is still in the head its just simply unplugged.
and I'm still not convinced its a mechanical issue, the first 4-5 seconds after a cold start up the engine will idle around 1500, then it will go into what ever mode its doing.

couple other shots in the dark, doesnt hurt to pull the plugs and have a look. then with it running in the state it is unplug ingnition coils one at a time just for curiosity sakes(might find something weird) and if possible find someone local and swap in another ecu

ill give that a shot see what happens but a different ecu wont be possible, 550 injectors and z32 maf.

[amnash]

what's your fuel pressure? if you don't have a gauge check my build thread for cheap engine bay gauge. and you should wire fuel pump to constant 12v through relay. there's a write up on skylinesaustralia. two cheap easy things to do that should be done anyways

[nick-nismo]

Fuel pump is already hardwired and fuel pressure is fine. I don't know if I mentioned this but the car drives fine, boost and pulls hard to redline. Just an idle issue

[amnash]

I don't know lol vacuum leak somewhere. goes unnoticed under boost