Idle Adjust Screw Has No Effect On Idle Rpm..

[Wacky Dee]

was just wondering what could explain how undoing the idle adjust screw on the AAC valve can have no effect whatsoever on the idle RPMs.. ? With the screw in completely or out completely it still idles the same.

Tuner first thought it was a leak and presssured the engine with a smoke machine but nothing came out so he concluded no leaks and we kinda left it at that. Any ideas?

I'm gonna try cleaning the AAC valve soonishly as per that DIY article so I thought I better ask about this in case I might screw up something along the way. Could my AAC valve gasket be leaking air in? Would that show up when pressured with a smoke machine ?

Edited August 2, 2009 by Wacky Dee

[Muff]

Bad luck dude.

i had the same probelm but only when the car warmed up.... because of forged pistons.

it would idle high and wouldnt be controlled by the aac valve.....

clean it out... but there is a good chance that its an vacume leak.... unfortunatly not all will show up with a smoke machine.... what sorta car is it... any work done??????

try blocking off the one way valve on the water manifold...

gl

[Wacky Dee]

don't have a high idle issue really ..sits steady at 850rpm once warmed up, just bugging me

do I have to disconnect the TPS while the engine is running BEFORE messing with the idle screw ? I just read somewhere last night that unless you disc the TPS the ecu will adjust to keep idle steady even if you're messing with the idle screw without disconnecting TPS

[Moodles2]

What is your car idling at?

It's possible there is a leak around the intake manifold since the gasket is paper, nothing a can of aerostart or brake cleaner won't find if it is a leak.

[Wacky Dee]

ok this is weird ...

I thought I'd take my AAC valve housing off and clean it with carby cleaner as per that tutorial in the DIY section ... once I unbolted the AAC housing one thing became quite clear right away, no need to clean it as it looks BRAND NEW inside .. I mean all the walls are shiny even the spring. No trace of carbon buildup or any dirt.

How's this even possible on a 10 year old car ??

[BASHO]

ok this is weird ...

I thought I'd take my AAC valve housing off and clean it with carby cleaner as per that tutorial in the DIY section ... once I unbolted the AAC housing one thing became quite clear right away, no need to clean it as it looks BRAND NEW inside .. I mean all the walls are shiny even the spring. No trace of carbon buildup or any dirt.

How's this even possible on a 10 year old car ??

Cleaned mine yesterday, hardly needed doing, (98 R34 GT-t 79000ks) same prob as you with the idle, I can set it to a perfect 650rpm when the ACC sensor is disco'd as soon as I plug it back in bingo back to just over 800rpm have phoned a couple of service/tuning people and the only answer I been offered that at least gives a possible reason is that they put on a few RPM at idle if they have a bigger aftermarket exhaust, as mine has a 3" dump and a 3 1/2" cat back I'm guessing I qualify there, but it still doesn't get to an idle adjustment solution.

I can get it down to 750 if I screw the idle adjust screw hard down but I'm not realy comfortable with that as it's obviously not a correct solution.

I've set the idle, sensor disconected, at 600rpm and it's giving me 800rpm sensor connected, the search for a solution continues.

[blind_elk]

What is the factory spec for idle speed?

The other thing is that the tacho may not be all that accurate - it could well be reading a bit high.

[REDGTT]

Best thing to do is hook up a nissan consult or nissan data scan with the laptop and read the tacho digitally.

[Wacky Dee]

if anyone can hook me up with the latest nissan datascan software please PM me getting my consult cable today..

[BASHO]

What is the factory spec for idle speed?

The other thing is that the tacho may not be all that accurate - it could well be reading a bit high.

It's 650rpm to set the timing and between 650 and 700rpm idle at normal running temp.

[NewKleer]

was just wondering what could explain how undoing the idle adjust screw on the AAC valve can have no effect whatsoever on the idle RPMs.. ? With the screw in completely or out completely it still idles the same.

if your not in base idle/timing mode then the ecu just adjusts the AAC to compensate?. e.g. u turn the idle down it opens the AAC more. turn it up it opens it less. though i would have thought at some point there should be a difference, but ive never personally tried doing it all the way one way or another.

[Wacky Dee]

how do you get in base idle mode, disc the TPS or somefin ?

[NewKleer]

ive never done it the manual way (something like disconnect tps and rev past 2k three times? dont know), easier to do it via consult cable/software (eg free version of conzult has it).

[BASHO]

OK guys looks like unless anyone knows a way of manualy getting in and out of the "IACV-AAC ADJ" program in the ECU we're screwed and orf to find a dealer/tuner who can perform this rather simple adjustment.

Here is the relevant page from the workshop manual you will need to clik the frigin thing a few times to get it up to full size once you've opened it.

And just to make our life a bit more fun heres a bit from the service manual :-

"Air/Fuel Ratio Inspection

CAUTION:

RB25DET A/T model uses exhaust pressure-sensative control muffler. Therfore,insert probeof the CO/HC meter into the left exhaust pipe. (under no-load condition,exhaust gas is emitted from the left exhaust pipe only.)"

Another possible reason for the overidle in the first place ?

FRAKIT, it's hard to remember when you're up to your as in crocodiles you only came to drain the swamp!

[NewKleer]

that page seems to indicate (as shown by the cross thru the consult terminal icon) that if you dont have consult you can enter base idle just by disconnecting TPS. i thought there were more steps but maybe not.

or u could just get a consult cable and do it via software base idle mode.

[BASHO]

that page seems to indicate (as shown by the cross thru the consult terminal icon) that if you dont have consult you can enter base idle just by disconnecting TPS. i thought there were more steps but maybe not.

or u could just get a consult cable and do it via software base idle mode.

I see what you mean, I took these steps to be all progressive , I'll give it a go and post the result.