Unstable Idle

[nismoskyline32]

hi there,

i have unstable idle for long time, it go up and down when stop at the traffic light even and i clean the acc valve.

and try to check all the hoses today.

and i found that unplug the hose from the nozzle( see pic with arrow) and the idle go very stable even i rev it up. but it suppose to be connected to the fuel regulator.

anybody know why? and can i leave it like that with no hose and find and another vacum hose go back to fuel regulator?

[Rekin]

my rpm's fluctuate occasionally when also waiting at traffic lights. An ecu reset seemed to reduce the amount of times it occured but i think i still have the problem.

Hopefully someone has a solution to this problem

[Rudager]

i used to get very erratic idle change with it constantly going up then down up then down every 15 seconds or so and i cleaned the AFM and AAC valve and it only does it now when the temp starts rising and the clutch fan kicks in.

[RANDY]

I would guess that the AAC valve is fluctuating between cold and hot, which varies the revs. Mine does it fairly frequently, but then on other days it's 100%.

When you disconnect the pressure/vac pipe for the fuel reg, do you block it, or just let the air come out? Be sure not to drive around too much with it off, I think the fuel pressure reg uses the vac/pressure from the inlet manifold to adjust the fuel pressure. You don't wanna get it lean on boost!

[mad082]

try cleaning your aac valve. thats solved my problem

[The Alchemist]

try cleaning your aac valve. thats solved my problem

One of many reasons for this

Often its the O2 sensor that has failed causing the Air fuel Base which is sort of a "learn" function in the factory ECU to alter to a positive or a negative change in the amount of fuel delivered at any given time.

As an O2 sensor can fail giving a high or a low or an "in the middle" voltage flatline the AFR Base can trim the fuel in varying ways with often more variable results in the real world.

This is why an ECU reset can "fix" the problem until the ecu RELEARNS again and stuffs everything up once more. This causes havoc at idle and lean cruise and causes many of the idle hunt and fuel economy problems that plaque skylines.

hope this helps,

Mike

Edited September 19, 2006 by The Alchemist

[Sarumatix]

Crickey for RB26 you have 2 of these O2 buggers to deal with >.< and the ACC valve is buried under the manifold! Woe is me with my idle problems!

[lows_13]

ACC valve

Clean AFM meter

Re-solder connect within AFM

O2 sensor

[khunjeng]

as simple fix might be a vacume tune has come off. Look at the small one used for the stock boost guage...Mine has come off a few times and does this.