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Help diagnosing erratic idle


keeweechris
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Kia Ora's

 

Just after some ideas on how to diagnose an erratic idle on a '99 GTB RevB. It's had that common minor shudder while idling for years (subaru thing?), but recently after a long trip it's got much worse. Doesn't stall, but tacho (dash) fluctuates between about 500-700rpm, and stutters and shudders every second or so. Feel like it will stall. No difference whether engine warm or cold. Once revs are >1500, runs and boosts well.

 

Things I've tried:

-Intake leak test (smoke). Nada.

-IACV - cleaned, and replaced with another from pick-a-part, but no difference

-AFM - Cleaned, but not tried with another yet (I need to get my hands on one)

-O2 sensor replaced with new (old had open circuit heater)

-All intake and vacuum piping checked & replaced about 3 months ago

-Air filter checked/cleaned

-BBOD cleaned and checked

-Boost solenoid (guard) checked and cleaned

-Injector plugs look fine

-Spark plugs replaced a few months back

 

Since it runs well under power, I figure fuel pump is ok? But it's on my list to replace the fuel filter soon.

 

I've got FreeSSM+VagCom hooked up and can get live values from the ECU/Sensors, if that's any help?

 

Thanks fulla's!

 

 

 

Edited by keeweechris
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Just realised what I haven't done is reset the ECU... doh. Will do that when home tonight.

 

Before replacing the O2 sensor, it popped code 32 (O2 sensor), so maybe it also stored some setting which mucked up the idle/mixture. I haven't reset the ECU since before the O2 sensor swap.

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49 minutes ago, keeweechris said:

Just realised what I haven't done is reset the ECU... doh. Will do that when home tonight.

 

Before replacing the O2 sensor, it popped code 32 (O2 sensor), so maybe it also stored some setting which mucked up the idle/mixture. I haven't reset the ECU since before the O2 sensor swap.

 

If you can get your hands on another AFM I would try that, fixed my GTB when I had one with that issue

 

I may even have a good AFM at home

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1 minute ago, TNHSTI said:

 

If you can get your hands on another AFM I would try that, fixed my GTB when I had one with that issue

 

I may even have a good AFM at home

 

Yeah, I need to borrow a good AFM to cross that off the list. Are you in Auck by any chance?

 

I removed the intake snorkel a few months back, so stock airbox takes air from inside guard. Think that would lead to AFM going bad?

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2 minutes ago, keeweechris said:

 

Yeah, I need to borrow a good AFM to cross that off the list. Are you in Auck by any chance?

 

I removed the intake snorkel a few months back, so stock airbox takes air from inside guard. Think that would lead to AFM going bad?

 

Na that wouldn't affect the AFM as I Removed that of mine as well with no issues

 

No I'm in Nelson but happy to courier it to you if I do in fact have it - will need to check tonight after work

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6 minutes ago, TNHSTI said:

 

Na that wouldn't affect the AFM as I Removed that of mine as well with no issues

 

No I'm in Nelson but happy to courier it to you if I do in fact have it - will need to check tonight after work

OK, thanks very much, that would be very appreciated.

 

It's this one, just in case you have a few different ones: s-l1600.jpg

8297-thickbox_default.jpg

If you can get the actual sensor out of the housing, that would be easier to ship.

Edited by keeweechris
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Well, ECU reset did nothing. I also cleaned the AFM, which did nothing.

 

Hesitates and tugs at light light throttle, no matter what rpm, if I'm cruising on the flat. But when applying a bit more right foot, it runs/accelerates smooth.

 

Also remembered that the old O2 sensor was quite obviously light grey, almost white. I've heard coolant is bad for it, and causes it to turn white. But I'm pretty sure it doesn't consume coolant.

 

Thinking at this stage either AFM, or injectors. Any other ideas?

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Can anyone interpret these values I got from FreeSSM this morning?

 

With ign on, engine off:

TPS 0.48v foot off, 4.26v foot to floor
AFM 1.02v
MAP -1kpa
IACV 115steps
Coolant Temp 22deg
A/F Corr 0.0%
Ign Timing 10deg
Diff pressure 1.96v
Neutral pos switch behaving

 

Idling from cold:

Timing hovering around 17-18deg. Revving 2000rpm, ign timing rises up to 35deg IS THIS NORMAL?
"Front O2 rich Signal" on-off-on-off... SHOULD IT BE CYCLING LIKE THIS??
Knocking Sig off
IACV 52steps, then dropped to 28steps after ~5min
TPS 0.44v (foot off pedal)
A/F Corr hovering around -4 to 0%
Temp rising normally to 60deg after about 5min
MAP -60kpa
AFM 1.2v. (2v when revving at 3000rpm) IS THIS IN THE RIGHT RANGE??

 

Thanks!

 

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On 23/10/2020 at 10:13 AM, keeweechris said:

Can anyone interpret these values I got from FreeSSM this morning?

 

With ign on, engine off:

TPS 0.48v foot off, 4.26v foot to floor
AFM 1.02v
MAP -1kpa
IACV 115steps
Coolant Temp 22deg
A/F Corr 0.0%
Ign Timing 10deg
Diff pressure 1.96v
Neutral pos switch behaving

 

Idling from cold:

Timing hovering around 17-18deg. Revving 2000rpm, ign timing rises up to 35deg IS THIS NORMAL?

pretty sure


"Front O2 rich Signal" on-off-on-off... SHOULD IT BE CYCLING LIKE THIS??

yes


Knocking Sig off

good


IACV 52steps, then dropped to 28steps after ~5min

sounds about right to me... cold start enrichment turning off after a few mins?


TPS 0.44v (foot off pedal)

looks fine


A/F Corr hovering around -4 to 0%

sure... sounds reasonable.


Temp rising normally to 60deg after about 5min

yup all good.


MAP -60kpa

this is approx 18 inhg which is good.


AFM 1.2v. (2v when revving at 3000rpm) IS THIS IN THE RIGHT RANGE??

sounds reasonable

 

Thanks!

NP!

 

Edited by Loren
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On 31/10/2020 at 8:05 PM, Loren said:

Have you tried unplugging each injector in turn to see if any of them don't make a difference to the idle?

It could help isolate the problem down to one cylinder.

 

Cheers, yeah, I did that. Each injector I unplugged caused the engine to change the way it ran, but surprisingly it did keep running, just. Yeah, I was hoping removing 1 injector wouldn't make any difference.

 

I got a coil and injector from pick-a-part yesterday, so will spend the week swapping each out in turn. Fun job huh.

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Unplug the MAF entirely and start it Maffless. Unsure about earlier revisions but the Rev-D runs openloop when its unplugged. Good way to troublshoot. 

 

If it idles fine wihtout the maf then thats possibly your probelem. 

 

 

Edit: just read above that you have already replaced the MAF with no difference.

Edited by A_J_T
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Have you checked the cambelt is on right? You could be one tooth off on one of the cam wheels.

 

Also have you checked the vacuum with a proper gauge? I know the ecu manifold pressure looked ok... though more borderline tbh.

Edited by Loren
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32 minutes ago, Loren said:

Have you checked the cambelt is on right? You could be one tooth off on one of the cam wheels.

 

Also have you checked the vacuum with a proper gauge? I know the ecu manifold pressure looked ok... though more borderline tbh.

Well, I did open one cam belt cover to check the belt wasn't damaged, but didn't check if it had skipped. Good idea though. Can you check without talking the centre cover and pulley off?

 

I kinda figured because there was a very clear point at 0psi where it started running well, and it boosted nicely, that the cambelt/timing was all good. Never experienced a belt with 1 tooth off before. And the problem is getting slowly progressively worse. But hey, no harm in checking, thanks!

 

I've got a cheap SCA boost gauge, and that looks to match the readings the ECU is seeing. What do you mean by "borderline"? Is -60kpa/18inHg not quite right? What's it a sign off?

 

Smoke tested again yesterday, and couldn't find any leaks.

3 hours ago, A_J_T said:

Unplug the MAF entirely and start it Maffless. Unsure about earlier revisions but the Rev-D runs openloop when its unplugged. Good way to troublshoot. 

 

If it idles fine wihtout the maf then thats possibly your probelem. 

 

 

Edit: just read above that you have already replaced the MAF with no difference.

Yeah, no change after swapping to pick-a-part MAF. The MAF's (mine and pick-a-part) look very clean though. So I figure the problem is somewhere else. Gotta try the easy stuff first though, right.

Edited by keeweechris
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18 minutes ago, keeweechris said:

Well, I did open one cam belt cover to check the belt wasn't damaged, but didn't check if it had skipped. Good idea though. Can you check without talking the centre cover and pulley off?

 

Yes you can check just by pulling the side covers back a bit... you just need to be able to see all the alignment marks.

Off by one tooth doesn't mean it will run bad through the whole range... but could make the idle a bit s***.

 

Quote

I kinda figured because there was a very clear point at 0psi where it started running well, and it boosted nicely, that the cambelt/timing was all good. Never experienced a belt with 1 tooth off before. And the problem is getting slowly progressively worse. But hey, no harm in checking, thanks!

 

I've got a cheap SCA boost gauge, and that looks to match the readings the ECU is seeing. What do you mean by "borderline"? Is -60kpa/18inHg not quite right? What's it a sign off?

 

You really need a proper vacuum gauge... not a boost gauge. 20 inHg is a healthy engine... less might be badly sealing valves... or cam belt off a bit. Do the compression test too.

 

 

Edited by Loren
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5 hours ago, Loren said:

Pick a part injectors? You are brave.

Have you done a compression test?


 

Haha, yeah, bit of a gamble. Came off a BH5B (same engine) at 255,000km.

 

No, comp and leakdown is on the list. No smoke/smell from oil filler, and only a moderate puff puff puff of air, so rings are prob ok I'm guessing? I'm pretty new to this. I'll have to get set up for a leakdown test.

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4 hours ago, A_J_T said:

Unplug the MAF entirely and start it Maffless. Unsure about earlier revisions but the Rev-D runs openloop when its unplugged. Good way to troublshoot. 

 

If it idles fine wihtout the maf then thats possibly your probelem. 

 

 

Edit: just read above that you have already replaced the MAF with no difference.

 

I haven't tried starting it without MAF though, but was curious how to force it into Open Loop. Are there map values for lower revs? I'll try this anyway, because if the bad idling (misfiring) sticks around, I guess it proves it's mechanical, fuel, or sparks, not sensor-related..?

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