Statek

GC8 fluctuating idle when warm, possible ECU issue?

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Hi guys

I've recently bought a 1999 WRX GC8. It's a non-STI, and all bits fitted are factory (as far as I can tell).

The problem I have is once it warms up, the idle starts hunting and it has a stutter when driving and trying to keep a steady pace (ie. while off-throttle in gear and on-boost it's fine). It's definitely over-fueling as can smell it while idling, and as it stutters it throws smoke out the exhaust.

The car runs absolutely sweet until it hits a certain temp - using the OBDII plug it looks like the problem starts occurring somewhere around 87C, but occasionally won't happen until around 94C.

The idle hunts between 200-1200 RPM, sometimes (rarely) causes the car to die.

Things I've checked:

- 3x AFMs plus a brand new one

- New plugs and checked resistance on HT leads

- Cleaned and tested the IAC valve

- Checked the specs on TPS

- Checked for vacuum leaks

- Bypassed turbo and intercooler (ie. fitted the AFM pipe straight onto the throttle body)

- Fuel pressure is about 38-40 psi at idle. Also fitted a fuel pressure regulator, and when it is running rich at idle, turned the fuel pressure all the way down to 10 psi but still doing the same thing.

- Found O2 sensor was dead. ECU seems to output around 0.3V on the O2 sensor input for some reason. We fitted a wideband, but ECU seemed to ignore it. Even when specified the wideband to output a steady 0.5V to the ECU, the ECU diagnostic was showing O2 voltage to fluctuate between 0.4V to 0.8V. AFR fluctuates between 10 and 13, matched to the RPM at idle.

- Visually inspected the ECU but can't find any obvious breaks.

Anybody struck this before?

Any ideas what else to check?

At best, I'm hoping someone will have an ECU lying around for me to try - 22611-AE481. I'm located West Auckland, but car is (sort of) driveable.

Edited by Statek

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Did you get a new O2 fitted? Sounds like the problems occurring when the ECU would be using the O2 the most.

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O2 sensor . It is supposed to flick or ping from rich to lean about 3 times per 5 seconds . Its how the xar finds best economy at stoich mixtures .the ecu purposely goes lean rich lean rich either side of stoich so it knows that its on the best af for stoich . Basically up or down a few injector % . Hence "narrow band " sensor . Its accurate for the narrow band right on stoich Cruise and idle . My car dud it for years . Replaced o2 with second hand new one . Had to check twice after that because my brain exlected it to hunt .

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Thanks for quick replies.

I got a 2nd hand o2 sensor from strongs, but its another dead one.

Any ideas on where to get a good aftermarket one? I'm thinking Bosch will be way better than Dasko.

I'm still wondering why the wideband didn't affect the idle at all... Or even why the o2 voltage fluctuated when we specified to output a steady 0.5v.

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I've received the o2 sensor, and I'm seriously impressed with partsouq.com. Original part for a fraction of the price in NZ, and really quick shipping. Awesome!

Chucked the o2 sensor in the car, reset the ECU and went for a drive.

It definitely changed the behaviour, but hasn't fully sorted my issue.

Prior to this replacement, the idle fluctuated wildly as soon as it hit a certain temp, but now with the new o2 sensor, the fluctuation has stabilized somewhat, but isn't cured yet. Now it seems to fluctuate less, maybe 500-1000rpm for about a minute, then it stabilizes and the car idles smoothly for a minute, before fluctuating again. Before this it would just start fluctuating and would get worse and worse.

While driving, it still has minor hesitation, but also noticed that at around 3600rpm it feels like a power cut.

Not sure what to try next. Almost certainly, I'll need another car to test fit parts to see which one will fix it - I'm still leaning towards ECU, but potentially coil pack? I don't know why a coil pack would cause the randomly fluctuating idle though...

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Some more internet reading is pointing at the AFM now, too. I've got 2 more at home, will try them tonight.

I guess it's possible that the o2 sensor was causing the bigger issue, hence swapping the AFM earlier did not make any difference. Now that this is reading right, it could be the AFM too...

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Tried a new AFM, and now have the idle sorted out.

Still have the issue of the car bogging down around 4000rpm. I suspect this one is now a spark related issue.

I'm running out of funds to just throw money at it. Before ordering a new coil pack, does anyone have one to try? Can discuss a deal with $$ for your help.

20160505_213154_zpsicl6ndd4.jpg

Edited by Statek

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Still waiting for the new AFM, which should arrive end of this week.

Haven't managed to get a coil to try, but I've re-gapped the BKR6E-11 spark plugs to a 0.8mm gap, which has pretty much sorted the bogging down issue. I'll get a set of BKR6E plugs and gap them to 0.7mm, and then see how it drives with the new AFM.

Definitely looks like I'm finally getting to the bottom of this.

Question: I've read a bit about this on the web, but the #3 spark plug isn't anywhere near as fouled up as the other 3. Just how "normal" is this?

58b56a13-22ea-4849-a3aa-a9fc549813ba_zps

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ive gota ver5/6 sti coil pack and leads, numbers are 22433aa430 and fho161 id sell if theyd work on a wrx

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 Statek said:
Still waiting for the new AFM, which should arrive end of this week.

Haven't managed to get a coil to try, but I've re-gapped the BKR6E-11 spark plugs to a 0.8mm gap, which has pretty much sorted the bogging down issue. I'll get a set of BKR6E plugs and gap them to 0.7mm, and then see how it drives with the new AFM.

Definitely looks like I'm finally getting to the bottom of this.

Question: I've read a bit about this on the web, but the #3 spark plug isn't anywhere near as fouled up as the other 3. Just how "normal" is this?

58b56a13-22ea-4849-a3aa-a9fc549813ba_zps

Are all four plugs the same heat rating?

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Could be weak ignition on the cylinders with black plugs, coil/leads or a much bigger gap on those plugs. Or it's running lean on cylinder 3, maybe a sticky or partially blocked injector.

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So I've now fitted a new OEM Air Flow Meter and reset the ECU. The idle improved again, but once more when it warms up, it feels like a light misfire.

Since then, I have also:

- replaced all the plugs with BKR6E, gapped to 0.7mm

- checked and then bypassed the PCV valve

- checked compression on all cylinders. #1, #2 and #4 were 180psi, #3 was 170psi

- since I can't bench test the injectors, I've swapped #1 with #3, but the issue is still on cylinder #3, so it's not the injector itself

- I've checked that all injectors have 12v, and traced the wires back to ECU. All the signal wires have less than 1 ohm resistance

- swapped leads over, just to be sure

Running lean on cylinder #3 makes me think that I have to try another ECU, as I'm either forgetting something, or there's just nothing else which could cause this issue, except the injector control.

Incidentally, the car is also running 0.5 bar of boost, and I believe it should be at 1 bar? It's got a TD04.

Reading one of the other current posts, I've followed the diagnostic procedures but can't find the issue either. I'm not so worried about the lack of boost at this stage, because if it's running lean I really don't want to blow it up. One at a time, I've done the following:

- I've checked that the restrictor pill is there, and even cleaned it up.

- I've checked that the Wastegate Solenoid is operating, and cleaned it out. Now it's ticking much louder, and blowing through it while it's ticking I can definitely tell it's opening and closing.

- I've blocked off the Wastegate Solenoid, but boost holding steady at 0.5 bar.

- Manually opened the Wastegate and let is slap shut.

- Blocked off the intake after the AFM pipe, and pressurised the system, but couldn't see/hear any leaks.

- Blocked off the factory BOV. This made it feel like the car is spooling up faster and that noise..... lovely.

I don't know if both the issues are related or not.

I'm all out of ideas.

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 Rosssub said:
Could be weak ignition on the cylinders with black plugs, coil/leads or a much bigger gap on those plugs. Or it's running lean on cylinder 3, maybe a sticky or partially blocked injector.

Have you tried another coilpack?

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 Rosssub said:
Have you tried another coilpack?

Still trying to get my hands on one. I've had two people offer coilpacks for sale, but neither is replying :confused:

I've also got someone with an ECU for an affordable price, might just pick it up anyway.

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Just to close off this thread:

Couldn't find any parts to swap, ran out of funds to buy stuff blindly to try and figure this one out. Sold car. Better luck to new owner.

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I know this is an old post but, Statek too bad you sold bro.

 

My car was having that exact same issue bro, my plugs were looking the same as well.

 

The issue turned out to be the Coolant Temp Sensor.

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