Idle Problem From Cold - Ideas?

[ausdrift]

Ok, so as of Tuesday last week I've now got an idle issue and despite searching the forums I'm not quite sure the cause, so am hoping for some imput and ideas.

The Problem

What will happen is when I start the car (typically from cold) it will be ok for a minute or so, then anytime I'm in neutral the idle will be hunting, going down as low as 200 and up to around 800, like a pendulum. If I'm driving with higher revs when I get into neutral the drop and swing of revs will be harder and it will be on the verge of stalling.

It will eventually close the range of revs until it gets to the 800 idle the car is set at. The longer I drive it the less it will hunt until eventually, say after 10 mins of city driving it will idle normally. Also, using AC or brakes doesn't appear to affect this issue.

Some specs

R33 GTST bigger turbo, 740cc injector, FMIC, exhaust, Z32 AFM, Walbro fuel pump and a Tune in December.

All of these parts were bought and fitted new within the last year.

In addition here are some common things to check regarding a poor idle that I've already considered.

- AFM poor soldering (unlikely as is a new unit)

- Vacuum/ IC piping - checked and were ok, and many have been replaced with silicon anyway

- ACC clean - done

- Fuel filter - replaced

- Plugs - 1 month old

- O2 sensor - 9 months old

- Coil packs - original, but are in good condition (and I don't think this issue relates to them anyway)

- Water temp sensor - original

What I think It might be

Seeing as my problem seems to be the regulation of air while the throttle body is closed, I'm thinking it could well be part of the Idle Air Control Valve system that is causing this. From what I can see there are two main parts, the popular one that people seem to talk about being the ACC valve. While I have cleaned the IAA unit (That's the wad hanging off the inlet manifold that contains the ACC, the cylinder hanging off the side) has anyone heard of that ACC unit being faulty or failing? Could it be a case of swapping this out?

The other suspicion I have is that it might have to do with the Air Regulator, which is the unit located below the IAA unit and connected by a vacuum hose (which continues back into the inlet plenum). According to the manual the air regulator is fully open below 20 degrees, half closed above 20 degrees and fully closed at above 60 degrees of water temp. This would seem to correspond to the times in operation that I will typically have this problem. Has anyone had this unit fail at all, or could it be cleaned back to good health?

And aside from this, is there anything that I may have missed which fits the symptoms of my idle problem?

Ok, thanks all

[admS15]

Cold start settings in tune.

[Sklyn]

assuming you are talking about a R33 S2 since you didnt actually say;

try cleaning the cold start valve as well

http://www.sau.com.au/forums/topic/410701-rb25-cold-start-valve-clean/

oh and since you had a 'tune' i guess that means you're not using the stock ecu.....?

might help if you say what ecu you have too, its a pretty major mod =)

Good work on putting up some useful info to get a reasonable answer though, hope you can sort it soon and let us know what it was.

[ausdrift]

The tuner did say that although he put in numbers for cold start he said should be fine (it was a heatwave at the time and he wasn't able to do a cold start), that I could contact him in colder months if there was an issue. That said, I don't think this is it as it happened suddenly last week and has persisted, which suggests its something failing.

And thanks for the link Sklyn, that's the air regulator I was talking about, so this will be an Easter task for me, regardless of whether this is the cure. Thanks.

And bingo, ECR33 Series 2 running a Power FC

[ausdrift]

Any other comments or ideas out there?

[89CAL]

If the tuner offered to look at it when it got colder I'd talk to him

Have a hand controller?

Watch the timing when the problem happens. Also watch the sensor/sw page for issues

The handcontroller is a little bit helpful in troubleshooting but will never be as good as logging on a laptop

[Dose Pipe Sutututu]

Do you have a wideband o2? I suspect not enough fuel in the water compensation table.

[ausdrift]

Nah, no wideband, never really looked into what they do. Is that something a tuner would be able to figure out and then tune for?

[Dose Pipe Sutututu]

to read AFR.. tuners would use theirs or yours to adjust fueling as required.

[zoomzoom]

If the other physical items like the air valves are operating fine, are you able to check the timing and fuel map?

Look for big changes in timing and fuel delivery in those load/rpm cells. A bumpy map can lead to oscillations in rpm due to lean-rich-lean cycles, or perhaps the same concept with timing.

[ausdrift]

Well, the latest. I removed the air regulator and was shocked to find..... It was clean. Very little residue at all, but I still fogged it with carby cleaner and reinstalled. Problem is still there, no surprise. Having run out of things I have the ability to check Ive decided Ill most likely take it to my tuner to diagnose. I also have a fuel economy problem so they can get both issues in one hit I think,

[Dose Pipe Sutututu]

obviously a bad tune

[ausdrift]

Took it back to the tuner, he checked everything, all came up ok. He also did an idle reset of the power FC so it learned the idle again and we thought the problem was fixed, but as I went to drive home it happened again. It at least all seems less bad than initially was but the reason is a mystery. He did note that my intake gasket is leaking so Im going to change that out; who knows, it might in some way help too....

[admS15]

Just a couple of quick and easy things you can check. If you have a hand controller, try changing the return to idle fuel cut off. Try increasing or decreasing it and see if it has any effect. From memory that should be on the screen where you set the idle. Also make sure that your car is idling at what your set point is. E.g if the controller is set at 800rpm but the engine is idling at 850, adjust the iacv so that the idle matches the set point. This had happened on a previous car of mine and was causing all sorts of weird idle issues. I adjusted the iacv to match and it ran beautifully.

[Dose Pipe Sutututu]

Does your car idle when you disconnect the TPS and idle control valve plug?