High idle problem

[bobbo]

I know there are postings on here already regarding this but my situation is apparently different... I think.
Car idles at about 1400RPM, starts perfectly, runs/idles smooth. Pulls great everything works and runs wonderfully except it runs rich.
I've had it to Nissan and we went over the car thoroughly. All sensors are in spec. Tried to adjust the idle both with the NON Consult method and with Consult. No luck.
The computer is trying to lower the idle by lowering the AAC valve to 2%. Should be about 40%. This also "suggests" the AAC valve is functioning properly. AAC valve has been completely disassembled and cleaned.
With the input of two tecks both with over 20 years experience the only thing they suspected is something was done to the ecu forcing the car to idle like that.
Does ANYONE have any suggestions?
I'm trying to make sure everything is working properly on the car before installing my PFC.
Thanks for any input!

[blkgtr02]

did you check the timing? my car idles at 900-1000 once it gets up to temp. I've tried adjusting the timing down to what the repair manual says and my car ran like sh*t. Bogs out under boost and when it hits boost its like vtec or something. Got my car tuned after that w/ nistune and everything was fine and I'm idling at 400 now with the same boost.

[evilgtr]

Hi bobbo,
Not sure if I can help but I had a similar issue once, my car was running perfectly but was just idling higher then normal. What it turned out to be was a small hose in the fuel pressure regulator vacuum line. I found it by pressure testing all the vaccum lines. As soon as I replaced that line it was instantly fixed.

[newalliance123]

Fixed mine by readjusting TPS to read .50v closed up from .38v...

[narface]

Make sure you have no vacuum leaks by checking all hoses for cracks, or loose fittings.

If that's not the problem, then check whether the air regulator is functioning properly. It's supposed to close the valve after the engine has warmed up to lower the RPM from a cold start.

If you have had your throttle bodies cleaned, that could be the cause. There is supposed to be a thin layer of throttle coat on each throttle plate to ensure an airtight seal when it is closed. Cleaning the throttle bodies will remove this coating and cause a leak. Also, check for broken throttle plates. If they are chipped on the edge, that's another leak.

It might be a good idea to replace all gaskets while you have everything apart, ie. AAC valve gasket, throttle body gasket.

[Skym]

Spraying around head to manifold joint with soapy? (creates bubbles where airleak is) water should show up any airleaks. Airleaks on intake manifold usually result in rpm going up and down (engine runs lean, o2 sensors make ECU run engine run rich and revs drop, leans it out due to hitting rich trigger and revs rise, then repeats) and engine running very rough at idle.

Check vacuum to AACV. The AACV and IACV can play up if there are any airleaks near vacuum source to AACV, IACV.

Also IACV can be faulty. But IACV can be tested on bench via hot plate (usually heat from engine) + voltage to IACV and note how long it takes to open.

Cracked hose to FPR reduces vacuum to FPR and fuel pressure can increase by around 7.1psi over the stock 35.5psi at idle. It should be obvious if you plumb in a fuel pressure gauge between fuel rail, fuel filter.

Faulty o2 sensors, misadjusted TPS (throttle enrichment) are other causes of engine running rich. Unplugging o2 sensors should force stock ECU into open loop where it ignores them.

[bobbo]

Thanks for all the tips!
Most of the advice you have all passed along was covered at Nissan.
If there is a vacuum leak it is so small it can't be detected by conventional means (visual, performance or spraying).
All of the sensors are in spec. TPS, MAFs, O2s ect.
The ecu is trying to pull the idle back as seen in the idle control menu in Consult. This indicates that the AAC is functioning plus the resistance is in spec. (9.5-10ohms mine is 9.9ohms).
The IACV likely isn't the issue because if they fail the tend to fail shut and the car cold idle very well if at all.
It is running rich which suggests a fueling issue so I'm going to try to replace the vac. line. We did try blocking and removing it at Nissan but made no difference.
I asked the guys at Nissan about the sealant on the Throttle plates and they don't think that would make nearly that much of a difference.
Also when they increased the opening on the AACV with Consult the idle started hunting. Not sure what that might mean.
Keep in mind this is a 450rpm idle increase. I would suspect that a vac leak bad enough to cause this would result in poor performance else where too.