Hunting Idle

[Td_d]

Meh, she's giving me grief. Sorted out the intercooler / meth nozzle, had the system pressure tested as well, all good. Now I've got a hunting idle, wings between 14.2 and 15.6 or so, sometimes less sometimes more, but noticeable and annoying. Another symptom is that on _very_light throttle it hesitates. Whilst idling, I actually managed to get it to stall but depressing the pedal very very lightly, and holding it there. AFRs went up a little to mid 15's, ran rough, and stalled.

Figured it might be the MAF, so pulled it, sprayed it clean and replaced, still hunting. I must note that with the MAF disconnected, it ran steadier - not 100% steady idle, but better.

Figure my MAF's shot? Anything else I should look at?

 

[Td_d]

Hmm.. I don't think it's the MAF. With the MAF disconnected (with the CEL of course), it displays the same behaviour, including the light throttle hesitation. I must add as well that when driving, it does the same thing with the throttle - but only very light (literally the 1-2% after it actually engages it).

 

[Td_d]

I'm thinking either throttle position sensor, or throttle body needs a good clean.

 

[Td_d]

Yeah, I'm thinking that too - but this feels like a mechanical issue that needs to be resolved first...

 

[Td_d]

Haven't yet implemented SD, so yes on the MAF maps. RPM is not hunting too bad - set at 850, it move maybe 50 rpms up and down, but I can see on the wideband AFRs are dropping to 14.2, and then climbing to mid, upper 15's, then reversing. Up, down, up, down. The fact that there's also the (very) partial throttle stall / hesitation makes me wonder if the throttle body does not need a good clean. Cleaned the TPS contacts thoroughly, but no good, still the same.

 

[Td_d]

Yeah, it's recent - but I had the injectors idling at 850 quite happily for a while. Fuel is not great - 91 - but I always use toluene, and the same petrol station, so I don't think that's a variable.

 

[Td_d]

Wondering whether its not a vacuum hose leak - but my AF learning A is not out of wack, and the system was pressure tested yesterday. I've noticed, and confirmed with the logs that it only happens when the car is almost at 'complete' vacuum (i.e. between -0.5 and -0.4 bar).

 

[Td_d]

So it looks like the vacuum hoses were the culprits. What gave it away was that driving home yesterday, boost wasn't feeling right, and the last time this happened, it was dirty filters on the HKS EVC vacuum hoses (also, boost 'pauses' at zero bar manifold relative pressure for a short while, for lack of a better description). Disassembles the filters, did a quick clean and refitted. Idle still not 100%, but nowhere near as bad, and the AFR oscillation at -0.5 bar / cruising condition is nearly all gone. I suspect if I actually replaced the filters, it would be completely gone. Bit of a pain, it's the second time this has happened...

These little buggers: