Help setting idle

[amnash]

for rb20det;
so ive been trying to set my idle speed for the longest time. its a mix between it not being set right and a rough idle.
i set the signal voltage on the tps to 0.5 with ignition on(engine not running)
with the IACV electrical unplugged i can adjust the the screw to get my desired idle speed(aiming for 1000rpm for now) and it has decent throttle response. then when i plug the IACV electrical back in the engine spikes up to 2000rpm and im pretty sure this isnt supposed to happen. the rpm adjustment screw on the ecu does absolutely nothing, and even if it did its only for a 250rpm adjustment(according to the fsm book)


could the IACV be broken itself?? i had taken it apart and cleaned it with carb cleaner during the build.

[MKIV]

I had a similar experience with my RB20. The previous owner drilled a hole into the IACV (don't ask) resulting in making it impossible to control the idle. I would start the car in the morning at 2200rpms and it would cool down to 1500 and bounce all over the place (even stall).

Once the IACV was replaced, never had issues again.

Hope that helped a bit.

[amnash]

ya i think ill take it off and take it apart clean it again and see how that works. drilled a hole in it..wtf?? lol

[Voodoo_ChildR32]

Taking mine apart and cleaning it out with brake cleaner worked wonders for my idle.


Sent from my iPhone using Tapatalk

[amnash]

just took both the idle control valve and cold start valve apart to clean. but look how clean these two are. i cleaned the idle control valve months ago so it was expected. but there is no way that cold start valve is original..it looks new.

i did a resistance check on the IACV and it was 9.5 ohm (9~10ohm in FSM)
put battery voltage to the cold start valve and it closed VERY slow it took about 5 minutes and it was only open a crack to begin with. how much is the valve supposed to be open??


EDIT: aacv valve is deleted.

[amnash]

since the cold start valve wasnt closed all the way..and the hoses were a little cracked on the ends i just took it out today and capped the ports.
my tps voltage is at 0.48 closed and 4.3 WOT. the idal control switch us making contact properly.
started it up and there wasnt much of a change. the engine is running very lean, fluctuating between 14~17.
there seems to be the SLIGHTEST vacuum leak sound coming from the idle control valve area but i cant find anything.
also fuel pressure is at about 45psi and when it starts to die pressure rises to around 50psi. there's a walbro fuel pump but shouldn't the fpr still regulate the pressure correctly?(40~42psi) the fpr came off a parts car

[Skym]

Should replace gaskets on anything you open up. I think AACV is a paper gasket, so should be able to buy paper gasket in same thickness and trace, cut out a new gasket.

The IACV should be fully open and slowly close as engine warms up. From what I understand IACV is affected by heat from engine. I assume that's why it's mounted on a intake runner. As far as I know, when testing IACV you use a hot plate.

The stock FPR should provide higher fuel pressure with bigger fuelpump. A adjustable FPR (Nismo, Sard, etc) or some say to drill out what I assume is a orifice? inside? stock FPR. Adjustable FPR is alot easier.

Stock fuel pressure should be around 35.5psi. At least that's what I worked it out to and 7.1psi higher with vacuum hose to FPR disconnected. But might want to check those to be 100% sure.

Airleaks or faulty IACV are usually the cause of higher than normal idle. Should be around 1300rpm when engine is cold if AACV and ECU are set at same rpm and drop to around 650rpm when warm.

Another cause can be MAF when it fails (MAF error code on stock ECU), as it idles at 1500rpm.

[amnash]

factory spec for fpr is 40 and 42 with vacuum undone. i dont see why it would be running lean with higher fuel pressure

[Skym]

Factory fuel pressure for RB20, RB26 is around 3.0 kg/cm2 when fuelpump is primed but engine isn't started or at idle with FPR vacuum hose removed. With vacuum hose connected it should be at around 2.5kg/cm2 at idle.

1kg/cm2 = 14.2psi

3.0kg/cm2 x 14.2psi = 42.6psi

2.5kg/cm2 x 14.2psi = 35.5psi

42.6psi - 35.5psi = +7.1psi (when vacuum hose to FPR is removed)

But that's with a stock fuel system.

A intake airleak can make engine run leaner. If airleak is big enough, the RPM needle on dash can fluctuate up, down due to o2 sensor making ECU change A/F ratio from lean to rich, then rich to lean.

[amnash]

ya thats^ what the fsm says (i swear i read 40~42 some where)

so my fuel pressure is a little high then.. that should be making the injectors put more out right? i checked all injectors while running and they all click, so that cant be the issue.
im 99.9% sure there isnt a vacuum leak.. ive checked everywhere with propane.
i took throttle body out and closed it all the way using the set screw, put it all back in with new gaskets. started it up and it idled perfect at 1000rpm at about 12~13afr, then once it warmed up with idle started to bog down with the afr being around 16~18.

so its leaning out after warm up.. could this be a maf issue? or pcv valve? the injectors are stock. ecu is stock. everything has been put back to stock for the engine break in. only mods are full 3" exhaust and a walbro pump. has grounding kit.

[amnash]

i have a nistuned ecu im gonna try. its for gtr injectors, exhaust, higher fuel pressure and fmic. my subi friend said on his car he had to get a tune just after installing a cat-back 3" exhaust. and mine is 3" from the turbo back. high hopes for the ecu..

[Skym]

At mid to high rpm it should run richer (where injectors are open more).

Fuelpressure could be higher when using stock FPR (too small orifice = less fuel returned to fueltank, fuelpressure rises), bigger lph fuelpump. Fitting a adjustable FPR (sort of adjust orifice size) allows you to drop it back to stock figures or the opposite.

Sometimes the intake manifold to head gasket fails and engine runs lean at idle (as mentioned above). Sometimes it's the gasket between top, bottom half of intake plenum.

Sometimes it's leaking between head, exhaust manifold and stock narrowband o2 sensor or a wideband o2 sensor is picking up the extra oxygen entering exhaust through the exhaust manifold leak. More oxygen = leaner A/F ratio. If rpm is steady, that's where I would look. It leaks on front or rear of exhaust manifold. Rear is usually the worst spot.

Also did you rewire the fuelpump wiring???? New relay, etc????

[amnash]

to answer your questions^

-the intake manifold gaskets are all new, lower half what installed engine out. both sides very clean, torqued to spec etc.. same as the upper half but with this gasket i sprayed with spray copper gasket maker a couple times before assembly. and ive gone around those two sealing points over and over again using propane torch with a long rubber hose. all seems dandy.

- the exhaust doesnt have any leaks. and if it did, like u said the idle would be steady and afr would appear all over the place but the idle is all over the place so that should rule out downstream of exhaust manifold?

-the fuel pump wiring has not been re-done.. u talking about the write up nelsonmx did? but the pressure seems fine besides it being a little high.

[amnash]

i also tried the other nistuned ecu today. but before i swapped them out i put in a different exciter just for shits.
The engine was cold so i turned it over and there was no change.. it ran fine at 1100rpm and about 10.5 afr. so i just sat there watching all the gauges and as it started to warm up the afr would flicker its way up about 0.1 every 3 seconds until eventually once warm it was out of control again getting 14~17afr and would only stay alive with my help and very unhealthy sounding.

i shut it off before something bad happened from running so lean disconnected battery and put the other ecu in. started engine and it was 10X worse. so that isnt gonna work at all... put the other one in and flashed the ecu using brake light method. started the engine, no change, let it idle by itself and let it just die on its own then i checked ecu for code got 55 all good.

[amnash]

help anyone? ill take a video today showing it