Help Me Diagnose My Weird Idle/near Stall Issue

[TUF250]

Hi all,

I have an R33 S2 GTST manual wit low ks in good condition. always serviced and only mods are a turbo back exhaust, bmc filter in std airbox and an r34 gt-t intercooler.

Right, now the car has a intermittant fault and I cant pick what it is. It used to do the typicall near stall issue where the rpm would drop then bounce up then drop again. I cleaned the aac valve as per the diy thread and it was fixed! great!

After a while it started doing something similar and i noticed a vac drop on my boost gauge, the car did the same thing, felt gutless and smelt of fuel. I found a vac leak which fixed that problem. great!

now the damn thing has come back again but its very intermittant. Somedays it will be completely fine. sometimes it will play up (eg of the fault, slow to the lights push the clutch in and the rpm will drop almost to 0, bounce up high and then slowly settle, when I try and take off it will hesitate and then settle. now whats weird is i cleaned my afm the other day and it went away.) NOTE when it happens the vac reads lower on the gauge but it goes back to normal idle reading when this problem dissappears.

After a while it did it again and the cleaning the afm didnt seem to fix it. i reset the computer and it went back to normal and after a few weeks it happened again...

I dont get it?? Any ideas?

(note. car has new plugs, coils are in good nick, it dosnt misfire, new fuel pump and filter, only run 98 etc etc)

Any ideas appreciated!

Thanks

[TUF250]

by the way just checked the fault codes by bridging the plug under the dash and got an error 55 which is 'system pass'

[Hanaldo]

Your latest problem, does it tend to happen when the car is warm? Ie. seems to run ok when cold, but starts playing up when the car warms up?

[lachlanw]

what blow off valve?

[leafybug]

maybe try a different afm or up your idle speed. i think most skylines get this problem though.. it happens to mine sometimes but not enough to worry me.

goodluck!

[TUF250]

standard blow off valve. seemed to often do it when its cold and actually improves when it warms but it can truly be all over the place. temp sits very stable and is not cold at all.

maybe I will buy another AFM, could this cause it?

[TUF250]

ok new development. really need some help with this one guys.

The car seems to be worst when its cold. once its at FULL operating temp (say 15mins after starting) it seems to be ok, although the vac is still a touch low.

I also reset the computer last night (discharged for 12hrs) and no change so thats ruled out.

Also when the car starts the fluctuating idle, if i take off and give it a little bit of go (just typical acceleration) the car seems to hesitate and stutter back and forward while accelerating then over a certain rpm will come to life. maybe this can help diagnose it?

Any help is VERY appreciated

thanks

Edited November 9, 2010 by TUF250

[KiwiRS4T]

Clean and gap or replace plugs check coils for cracks, shorting.

[TUF250]

already done, replaced plugs note even 5,000 ago with bcpres with a 0.9 gap (car runs std boost) and coils checked out fine.

remember its an idle hunting problem and the car stutters and pulses as you accelerate then picks up all lost power at about 2500 to 3000. if it was coils it would show up in the higher rpm band from what I have read.

im going to try a replacement afm tonight and see what happens

keep the ides coming.

there seems to be alot of people that have had this issue but no one has posted up their results

[TUF250]

just for future SAU members. The problem was the AFM. put in a replacement and its good as gold. thanks!

[awhiteone]

Glad u sorted it, I've been following this as I occasionally get the same problem.

Do you also get bad fuel economy? Sometimes I get bout 250-275 from a full tank with mixed city and country toad driving. That's about 14-15 l/100km which isn't good.

Does the afm get used in fuel calculations all the time? My other car has a MAP sensor instead so wondering if the AFM does the same. The other thing might have been O2 sensor but that would give you rough running after warmup if it wasn't working.

[DOHC]

got the same problem here.. almost just 250 per tank.. where can you get afm?? can you get it brand new? where to get it?? nissan?? how much?

[DVS JEZ]

U guys with bad fuel economy should get a new 02 sensor

[TUF250]

yeah i replaced my 02 sensor a while back. got it from bursons for about $100. When the car was carrying on, which didnt happen all the time the economy was bad. but once it settled it seem to go back to normal. afm can dictate mixtures to a degree but when it was playing up you could smell fuel. probably the computer trying to compensate.

you can buy them new from nissan. would be big $$$ though. Look around in the for sale thread. usually some floating around otherwise put an add up in the wanted dection. i did and got heaps of replies

[Plan-FAILURE]

Hi all,

I have an R33 S2 GTST manual wit low ks in good condition. always serviced and only mods are a turbo back exhaust, bmc filter in std airbox and an r34 gt-t intercooler.

Right, now the car has a intermittant fault and I cant pick what it is. It used to do the typicall near stall issue where the rpm would drop then bounce up then drop again. I cleaned the aac valve as per the diy thread and it was fixed! great!

After a while it started doing something similar and i noticed a vac drop on my boost gauge, the car did the same thing, felt gutless and smelt of fuel. I found a vac leak which fixed that problem. great!

now the damn thing has come back again but its very intermittant. Somedays it will be completely fine. sometimes it will play up (eg of the fault, slow to the lights push the clutch in and the rpm will drop almost to 0, bounce up high and then slowly settle, when I try and take off it will hesitate and then settle. now whats weird is i cleaned my afm the other day and it went away.) NOTE when it happens the vac reads lower on the gauge but it goes back to normal idle reading when this problem dissappears.

After a while it did it again and the cleaning the afm didnt seem to fix it. i reset the computer and it went back to normal and after a few weeks it happened again...

I dont get it?? Any ideas?

(note. car has new plugs, coils are in good nick, it dosnt misfire, new fuel pump and filter, only run 98 etc etc)

Any ideas appreciated!

Thanks

Yeah I'm having an issue like this with my '93 R32 GTS-t. I'm running a big stereo as well which, when playing beats, increased the gravity and frequency of the near stall/hesitation on moving off from idle and hesitation in low revs.

With this in mind, I started by replacing the battery as it was proper fu**ed. This improved things 10 fold as the new one has 580 CCA and can handle the stereo as well as the cars electrical needs but I'm still getting the occasional hiccup (which 99% of the time occurs when I stop and pick a friend up, but is only present for a few seconds.

I think AFM will be next - I'm gonna give the z32 a clean and see what happens.

If cleaning the AFM doesn't completely eliminate the problem I'd be testing the ignitor chip and the voltage to the fuel pump.

I have new splitfire coil packs, recently regapped plugs and I have recently replaced fuel filter.

I'll let you know how I get on with mine but this seems to be a pretty common issue with the early RBs (20 and 25).

[phat_man]

Your latest problem, does it tend to happen when the car is warm? Ie. seems to run ok when cold, but starts playing up when the car warms up?

What does it mean if it does this while its warm?