Problem With R32 Gtst

[Hanaldo]

Hey guys,

My mate has just bought a 1989 R32 GTST off a member on here which we are currently having some problems with. He has just had the radiator and all the heater hoses replaced, as well as a complete service.

Now when he bought the car we noticed it was idling really high, at about 1300rpm. We didn't really think much of it, put it down to needing it's idle adjusted. He took it into his work one day (he is an apprentice mechanic for Western Power), and his work colleagues tried to adjust the idle stepper motor but it didn't do anything no matter how much they adjusted the screw. So they disconnected the AAC by disconnected the vacuum hose that goes to it and plugging up the hoses. This made it idle at the correct rpm, but it also started hunting when warm. The mechanic he took it to for the service had a look at it and suggested cleaning the AAC or possibly replacing it.

So when we got it back i took off the AAC and cleaned it, put it back on and it still didn't work, if anything it got worse. So i drove it from my house back to my mates house (a good 20kms), and when you are accelerating it drives perfectly fine, no problems, boosts fine (although boost gauge reads 12psi so potentially overboosting?). But when on vacuum (cruising or decelerating), the car lurches pretty horribly. The car doesn't stall, although when it hunts (usually hunts between 1500rpm and 2500rpm) it sometimes drops so low that the car almost stalls, like the accessory lights (battery, oil, etc.) all flicker, but then the car seems to rev itself and it won't quite stall.

We replaced the AAC today and used CopperMax to make a gasket, but the problems still persist. So my guess would be there is a vacuum leak somewhere? If so, would anyone be able to suggest where we start looking, or could it be anywhere in the engine bay? If not, what else could be causing this? Car is pretty much all standard, just has a full 3" turbo back exhaust (with split dump, which may be causing the overboosting?), pod filter, and now has a brand new alloy radiator.

Any help would be very much appreciated,

Thanks,

Martin

Edited June 2, 2010 by Hanaldo

[Dsturbd]

I found this , it may help you in your quest

http://www.skylinesaustralia.com/forums/Co...-B-t191756.html

[bubba]

Check ALL vaccum hoses, there are some troublesome ones under the throttlebody.

Also, why did they block off all the hoses to/from the AAC?

Adjusting the stop screw is only one way of physically adjusting the idle, there is also a little screw on the ECU that electronically adjusts it.

It's not running an atmo bov or catch can is it? Tried cleaning the AFM?

[Hanaldo]

Check ALL vaccum hoses, there are some troublesome ones under the throttlebody.

Also, why did they block off all the hoses to/from the AAC?

Adjusting the stop screw is only one way of physically adjusting the idle, there is also a little screw on the ECU that electronically adjusts it.

It's not running an atmo bov or catch can is it? Tried cleaning the AFM?

They blocked off the vacuum line to the AAC to stop it idling so high. Not sure how it worked, because as you said it should be the only way of adjusting the idle mechanically. It did lower the idle rpm, it just caused it to hunt.

And no, everything is stock apart from the things i mentioned above. We haven't tried the AFM, can give that a go if you think it may be a culprit? I had thought of it, but i thought if the AFM was stuffed or dirty then it wouldn't accelerate fine would it?

[bubba]

It it was completely stuffed then it would probably going into limp mode, if it's just a bit dirty it would probably just run lean or rich, not sure which but I would lean towards lean as it would probably not be reading as much air as was actually coming in. This would make trying to hit the target idle AFR (stoich) hard as it thinks it is doing one thing but it's actually doing the other.

I'd give it a clean just to be on the safe side and maybe try swap the AFM and AAC with known working units.

Also, cleaning the AAC will do nothing if the bypass hose is no longer connected.

I would return everything to stock, clean the AFM, check and/or replace all vaccum hoses (can be hard to identify a split/cracked hose) and take it from there.

[snozzle]

is the throttle body completely shut on idle? if there is a leak in the throttle body, the idle control valve wont change a thing and it will idle higher than normal

[Hanaldo]

It it was completely stuffed then it would probably going into limp mode, if it's just a bit dirty it would probably just run lean or rich, not sure which but I would lean towards lean as it would probably not be reading as much air as was actually coming in. This would make trying to hit the target idle AFR (stoich) hard as it thinks it is doing one thing but it's actually doing the other.

I'd give it a clean just to be on the safe side and maybe try swap the AFM and AAC with known working units.

Also, cleaning the AAC will do nothing if the bypass hose is no longer connected.

I would return everything to stock, clean the AFM, check and/or replace all vaccum hoses (can be hard to identify a split/cracked hose) and take it from there.

Yeh we have already replaced the AAC, and have connected all the vacuum lines back up again.

is the throttle body completely shut on idle? if there is a leak in the throttle body, the idle control valve wont change a thing and it will idle higher than normal

Hmmm that seems like a good suggestion, how do we check if the TB is completely shut? Also, would that cause the lurching while driving? Because it only does it on deceleration and cruising, not on acceleration...

[snozzle]

not sure of the exact implication of a leaking throttle body but the easiest way to check is to take the piping off that attaches to the throttle body, possibly even take the throttle body off the plenum and check, also there is an adjustment screw that stops the throttle body from fully closing, that should be wound back all the way so the throttle body is allowed to fully close.

if this doesnt fix it, you have a vacum leak sumwhere or a vac line in the wrong place, these problems are one of the most time consuming to fix lol

[bubba]

I'm not sure you WANT the throttle plate completely closed at idle.. that might be causing the surge on decel and the hunting at idle as the AAC is trying to do more than it was meant for..

I could be completely wrong but to my logic you need to have the throttle plate open ever so slightly at idle (hence the use of the stop screw to set the base idle) and then the AAC is there to adjust for extra load from aircon, headlights etc etc.

[dose_it]

yes i understand this is my car. did he replace the hose and sensor i told him to replace in the first place? which i told him was causing the problem? its got nothing to do with the aac valve. theres a thickish hose that runs under the plenum which is disconnected and blocked and when connected it causes hunting and shit. the hose goes to a sensor as far as ive been told replace the hose and sensor and it will sort it out. aac valve then may need fiddling with after thats rectified first

[dose_it]

[Hanaldo]

yes i understand this is my car. did he replace the hose and sensor i told him to replace in the first place? which i told him was causing the problem? its got nothing to do with the aac valve. theres a thickish hose that runs under the plenum which is disconnected and blocked and when connected it causes hunting and shit. the hose goes to a sensor as far as ive been told replace the hose and sensor and it will sort it out. aac valve then may need fiddling with after thats rectified first

We will check it out, cheers man. What is the sensor for do you know?

[dose_it]

no idea at all

just what workshop told me needed doing

[99 GTT]

Hmm you could be talking about the Air Regulator. Is the hose thats blocked off short and comes out the bottom of the plenum almost 90 degrees towards the firewall and into the sensor?

Sounds to me like this is what you are talking about as when broken they cause high idle etc.

Edited June 3, 2010 by 99 GTT

[dose_it]

yea sounds about right vaguely remember it having a 90 degree bend on it. anways thats what i got told the problem was and passed it on to the new owner.

martin. i even told tom i could source the part for him if he need be. but if you take a photo of it and go to any jap shop they can take it off another motor

[Hanaldo]

yea sounds about right vaguely remember it having a 90 degree bend on it. anways thats what i got told the problem was and passed it on to the new owner.

martin. i even told tom i could source the part for him if he need be. but if you take a photo of it and go to any jap shop they can take it off another motor

Cheers man. If it is that then i am going to slap him round the head lol

[99 GTT]

Cheers man. If it is that then i am going to slap him round the head lol

If the hose i talked about is blocked and the problem, then i can post pics from the service manual and also the part number for you if that helps.

Let me know if you need them.

Best of luck.

[Hanaldo]

Cheers mate, should be looking at it tomorrow sometime, i'll let you know

[XxNinjaxX]

if you need any parts ordered, im more than happy to help out. I work at nissan so i get parts cheap cheap just give me the part number and i'll give you a quote, only condition is payment must be made to me before ordering to ensure im not stuck with the bill

[Hanaldo]

if you need any parts ordered, im more than happy to help out. I work at nissan so i get parts cheap cheap just give me the part number and i'll give you a quote, only condition is payment must be made to me before ordering to ensure im not stuck with the bill

Cheers man

Well i haven't had a look at the car yet, but my mate has said he looked for the blocked off hose and sensor that Keith was talking about and said he couldn't find it, everything seems to be connected. Throttle body is also fully closed at idle... So we are still unsure of what it is. I would like to take a look at it myself because i think i know the hose that Keith was talking about, but until then we are still stumped