Hello -

1994 converted to a single turbo with all vacuum lines replaced by a previous owner. Since owning the car past two years, it idle hunts intermittently between 1100 and 1600 RPM. It will often start after the enrichment phase and maybe 50% of the time at a stop light or sign (drifting or sitting still, no clutch depressed or pushing clutch in has no impact). Typical idle when not hunting is around 900 RPM. Things checked -

1. Vacuum leak - replaced UIM, LIM and injector seals and retested at a professional shop with no vacuum leak found
2. Adjusted TPS
3. Ensured that the throttle cable is not sticking
4. MAF reading ok on Power FC
5. Clutch switch appears to match open / close on Power FC
6. Saw Dale Clark's note about about cleaning the ISC. Removed and cleaned thoroughly and reseated

What else can I check outside of finding someone who does tuning? It seems strange to me to be a tuning issue since it is so intermittent (yet persistent!)

TYVM.

 

based on what youre saying it could go either way. a tuner would be able to quickly identify whether its an issue with the map or a mechanical issue. sounds like you did everything right as far as troubleshooting. if no vacuum leaks were found then it makes it more likely to be a tuning issue. sometimes if the values in the fuel table are off it will cause exactly what youre describing. it may just need some minor tweaking considering its intermittent.

 

Faulty oxygen sensor?

 

Hes single turbo. I'm hoping he didn't waste the time putting a bung for the stock o2. He's also on a pfc so o2 feedback should be off anyway

 

the PFC (and stock ecu) need a couple of things to idle happy. the PFC needs to be able to hit its target idle speed, so if the car is idling at 900, but the setting is 730, it will have problems.
also the idle and fuel cut settings are related, so if they are too close or too far it will do odd things.

and third it helps to turn the AAS screw in all the way and then back it off about 1/2 turn or so. the BAC valve itself is kind of run like an injector, and like an injector there is an area that isn't linear at low duty cycle. the stock ecu wants ~38% duty at idle, if its too low idle won't be stable pretty much no matter what. the BAC valve is in the logs.

i need to do this to mine also, but you just warm the thing up, turn on the datalog at idle, and then you can try different idle speeds and mixtures and such. with mine i need to do mixture, the autotune leaves it kind of lean