Idle Hunting. Yes, I've Searched.

[M E S O G L E A]

When cold, it hunts and the VCT solenoid actuates on and off. I believe the cam advance causes stumble increasing the hunting. If I disconnect the VCT, it still hunts but no as bad.

After it warms to operation temp (80 C +) it will hunt less. Once it stabilizes, it idles fine. Blip the throttle and it will hunt.

If I turn on the A/C, it shoots to about 1200 RPM.

I've cleaned the AAC and MAF. I tried 3 times to find vacuum leaks with a can of spray cleaner. I've replaced vacuum lines. I swapped out a spare AAC. I've checked all the intake pipe couplers.

I replaced the igniter (holy fluxing expensive for 6 transistors!), coils and spark plugs.

My tuner looked at it, he checked the timing and used cleaned to test for a vacuum leak this afternoon and thinks its the AAC valve. According to the PFC display everything is fine. I'm setting up an appointment repair tomorrow because I'm getting madder each time I attempt to troubleshoot. He has no clue because the symptoms are vague.

It drives fine, it just refuses to idle. I'm pulling my hair out over this.

Any ideas?

[MBS206]

You say you have a PFC

When did it go in?

Have you done an idle learn?

[M E S O G L E A]

Yes, it was tuned at Fujii Dynamics.

[paulr33]

are u sure? does VCT under SENSOR SW CHECK illuminate at idle?

VCT is only meant to engage when the following are true

NTR is not ON

THR is more than 0.30 (ie not closed)

RPM > 4700 rpm

i dont see how VCT would be on at idle, unless you have throttle open and not in nuetral (or something is broken)

[paulr33]

but either way it just sounds like theyve done the self idle learn wrong

no biggie - read the PFC FAQ in my signature and away you go - takes about 30 minutes to do yourself at home, but youll loose the tune

make sure you copy down the tune before you do it

[M E S O G L E A]

The RPM's increase and that turns on the VCT. The VCT causes stumble under light acceleration. The stumble drops the RPM's. The AAC tries to compensate and over-corrects. Repeat.

I don't think Fujii did the tune wrong, he looked at the PFC display twice already saying all readings are withing normal parameters. I don't like the idea of messing with a $1200 tune.

[Rezlo]

Welcome to the wonderful world of PFC's terrible idle control, random doesnt even begin to explain it.

What I find has the biggest effect on the idle when you have a PFC is the TPS sensor, you need to get it JUST right and it will idle spot on, also that you have the throttle stop set just right that its not having to use the AAC to compensate more than it has to. In your case if the VCT is kicking in its a sure sign the TPS voltage at idle is to high, dont change the map just set it down just a hair at a time till the problem resolves.

With all my SR's and RB's im doing now im fitting VEMS managment, I got the last car i did to idle without any AAC better with the the VEMS than my car ever has with the PFC, though I must admit I find the idle on the D-jetro system better than L-jetro.

Edited November 15, 2008 by Rezlo

[paulr33]

so again, you are saying that VCT is coming on at idle?

this is not correct and not by design - ie something is broken

VCT should not engage at idle - so if you can fix that, youll probably fix your problem

the PFC idle either works or doesnt, generally when it doesnt work the engine is at fault

ie a toast sensor, a toast mechanical part etc.

[The Dan]

If you are running a charcoal canister, block the hoses with a pair of pliers when it hunts and see if this corrects the issue.

Unplugging the VCT and idle change are a by-product of one another, unplug the TPS and the idle will change too, that doesn't mean the TPS is faulty though.

[MBS206]

so again, you are saying that VCT is coming on at idle?

this is not correct and not by design - ie something is broken

VCT should not engage at idle - so if you can fix that, youll probably fix your problem

the PFC idle either works or doesnt, generally when it doesnt work the engine is at fault

ie a toast sensor, a toast mechanical part etc.

Paul, not sure how the PFC does it, but I know the factory computer on the R33 GTS-t runs the VCT OFF at RPMS BELOW 1050RPM, so it's on above 1050RPM, UNTIL, it hits above 4750 from memory it is, where it switches off again.

It actually sits and idles with VCT off, should come on when revs go higher then 1050... Hence, if it's hunting, it's reasonable to expect VCT should kick on and off if RPM is going above and below 1050RPM, UNLESS the PFC doesn't follow the factory computer setup.

[M E S O G L E A]

I set up an diagnosis appointment with my tuner for next week. We set a initial price limit of 50000 yen to search for the problem.

How do I copy the tune if I don't have the PFC software? Can I get the info off the hand controller?

My main issue is that I'm leaving Japan and I cant take the car. I've spent way too much on this car because I expected to be able to stay at least 3 more years. I know I'm going to get screwed of the sale but if it doesn't impress a potential buyer the first time, it wont sell. A jacked up idle will turn away any buyer.

[Rezlo]

I set up an diagnosis appointment with my tuner for next week. We set a initial price limit of 50000 yen to search for the problem.

How do I copy the tune if I don't have the PFC software? Can I get the info off the hand controller?

My main issue is that I'm leaving Japan and I cant take the car. I've spent way too much on this car because I expected to be able to stay at least 3 more years. I know I'm going to get screwed of the sale but if it doesn't impress a potential buyer the first time, it wont sell. A jacked up idle will turn away any buyer.

1X screwdriver

1X person in car watching TPS voltage

2X Minutes working, drop it by .1v at a time, usualy its only SLIGHTLY higher than it should be.

= corrected idle

99.99% of the time its the TPS voltage that is to high that makes the idle do that on the rb25 w/pfc.

[M E S O G L E A]

TPS set at .45 VDC, tuner says that is fine.

So I should adjust the TPS above or below this?

[RB JET]

Holy crap my problem is exactly the same as this, i can hear the vct solenoid clicking on and off, and the idle hunts around. Just had pfc put in about a month ago. Been searching for vacuum leaks (none) cleaned and adjusted my aac valve, adjusted tps (but by adjusted i just went straight to .35v, didnt try it on different voltages) and it still hunts around!! Please keep updating this thread (i will too), we should work together to solve this shit of a problem!!!

[M E S O G L E A]

I'm going to try Rezlo's method and gradually adjust the TPS tomorrow after work. One of my neighbors gets all butt hurt if the car idles (or attempts to) in my parking area for too long.

[RB JET]

I'm going to try Rezlo's method and gradually adjust the TPS tomorrow after work. One of my neighbors gets all butt hurt if the car idles (or attempts to) in my parking area for too long.

Me too. Ill adjust mine and post up how i go. Let me know how you go too. I just tried the charcoal canister blocking off, no change.

Edited November 16, 2008 by RB JET

[M E S O G L E A]

I changed vacuum hoses and then blocked them off, no change.

Whats up with the air regulator under the manifold?

[M E S O G L E A]

TPS adjustment didn't do much.

The PFC displays X.XX volts DC. I don't know how many decimal places the PFC actually reads voltage.

If I had the software and cable, I would save the tune and reinitialize the idle. I'm positive that's what it needs because off throttle its great and boosts over 18 PSI with knock readings well within limits.

I hope Fujii can fix this.

[shaunzo101]

my idle hunting problem in my car just slowly went away over time, i think it got better when i was using the air-con strange enough.

[M E S O G L E A]

I'm positive it’s the idle learn on the PFC or the TPS setting. It's not the TPS, I installed a spare.

I disconnected the AAC and it wont idle high with the A/C on.

I disconnected the VCT solenoid and it wont idle hunt after blipping the throttle.

I disconnected the TPS and the idle is fine and the VCT will not actuate.

It’s a killer street motor. Fast response, about 350HP at the wheels yet drives like a kitten if your foot is not in it.

Basically it’s a great car if its not idling.