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Subaru ej205 idle control issue with lightweight components

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Hi all, I have an 02 WRX Im working on the idle control with. Everything is in pretty good control except for the case when the engine is cool and I run the A/C. If the engine is under about 150f the idle can drop low and nearly stall when I push the clutch in coming up to a stop. warmed up everything works normally. The engine has mid level cams, TGV delete, lightweight crank pulley and flywheel, and an open exhaust with a larger turbo. I am tuning with the Cobb accessport on a factory ecu. I notice a lean condition on the WBO2 at the same time the idle drops low.

I have the idle turned up as much as I would like without being excessive. In my case the factory ecu doesnt have base solenoid control like an aftermarket unit. So I think I can only use the maf curve, closed loop fueling compensation, and idle timing for adjustments. Any good methods for this?

Perhaps you should investigate your compensations, running a bit richer when cold, or with a bit more advance may help. Of course your idle speed may just need to be higher when the engine is cold as well.

You should have RPM and timing Target tables for specific idle conditions such as AC load, coolant temp compensation etc. Take a screen shot of some of your idle settings and I can give my opinion.

I assume mid-level is something like a 272? In general I'd say you'd want to bump idle up roughly 200rpm and add some timing. You may also need to target slightly richer than stoich and/or force an open loop idle.

I've had a very similar setup in the past and it eventually had perfect driveability.

OK thanks see attached. The AC idle is just a minimum value set to 1050. stoich target is 14.65. Looking at the tables I realize the closed loop compensations actually push the target lean slightly. The idle will usually drop to ~500 and then pick up to target. Sounds like I should push the values a little rich in the idle area and maybe add a little timing as the engine is on the way down from 2000 rpm? Oh and the cams are 272. Drivability wise it feels like it could probably use a little richness near idle anyway.

Attached Files

Looks like your timing is stock and you have plenty of RPM. I'd try more timing to end up with less RPM and then only use richening of the AFR if you have to.

For reference I ended up at 960rpm with 15deg of idle timing and it was pretty good at 14.7 AFR but slightly better at 14.3. I also didn't have to add any extra RPM for high electrical load/AC conditions, but you may have to add another 50-100rpm there. However, this all assumes that your MAF is scaled properly and not enormous (80+mm). Coming up to a stop and stalling can certainly be a MAF related issue, but if that's all sorted then having some more idle timing will definitely help. Also pay attention to what your primary ignition table has for numbers in the applicable cells leading up to an idle condition.

Thanks for all the help, I added a little timing and fuel and it's sorted out nicely. The maf is actually in a larger bore, 73 mm, and is within a few percent on closed loop fuel trims. about 13.5 deg at idle with some ramp down from 2000rpm.