Subaru Forester engine light/poor idle

pete4130

I've got a 2003 Subaru Forester, 2.5 XS with about 207,000km. I've had it since about 185,000 km/2 years.

About 6 weeks ago the engine light came on. My local mech I go to is a Subaru specialist and extremely good.

The fault code was the Idle control valve which he reset. 2 weeks later the code engine light came back on. It was due a service and left it in. Service was done and ICAV was taken out, cleaned and put back in free of charge.

About 2 weeks later, the engine light comes back on. Same fault code. My mech swapped it out for a used ICAV unit (only about 50,000km on it) and paid about AU$165 for that. No more fault code but the idle was very high and the car was racing away in 2nd gear, keeping higher than normal RPM when off the throttle. At traffic lights it would sit at 1500 RPM and eventually drop to 750RPM. I started the car (warm engine) yesterday and the idle dropped so low it stalled out. Brought it back to my mech and he put a 3rd ICAV for no charge in and explained its very unusual for them to go, so for a 2nd one to act up its more than likely the ECU or wiring loom. He also put another ECU in for no charge for the time being to eliminate the ECU and only need to pay if the problem doesn't reoccur.

Everything seemed to be fine the past 24 hours and then the engine light came back on and the idle was very high again. With 3 different ICAV untis and 2 different ECU's, what else could the cause be, apart from a dodgy wiring loom that could be causing the problem? I've read could be throttle body or throttle cable?

I can't get back to him until Monday to get it looked at again. I'm just looking for any other experiences with Foresters and poor idles. Plenty of info online that fit my description but nothing definitive to my situation.

Special Circumstances

Could it be a dirty throttle body? The iacv and throttle body would both need to working right for a proper idle.

I'd say a hunt through subaruforester.org would be worthwhile. Quick search indicates "neutral switch" can give trouble and lead to strange idle behaviour and codes.

pete4130

Yeah, I've seen the neutral switch come up in searching. It's just so inconsistent. First time the engine light came on, it'd be off when the car was started the next time.

I've seen the 3 ICAV units that were put on and 3 can't be bad.

First thought when I saw the light was the CAT had gone. Luckily its something small like ICAV or throttle body which isn't too much to get put right. It's just trying to eliminate what its not.

Like I said, My mech is a really good Subaru Specialist and any issue I've ever had he's pretty much diagnosed before even lifting the bonnet and gone out of his way to avoid any extra cost to me.

I'm just sick of the warning light coming on every 2 weeks.

jimgoose

Bit of dead-chicken waving: when an ICV is replaced, some systems need around six or eight power-on, wait for instrument lights, power-off cycles to calibrate the new unit.

Ded_Zebra

Another thing it might be is a worn throttle body. If there is excessive free play in the pivots of the butterfly the throttle could close different amounts every time it shuts. Basically not closing all the way every time depending on were the butterfly has wiggled to. This would mean the car will have very changeable idle quality. This extra air getting in may also make the ECU think the ICV is bad.

pete4130

As it turns out, the ECU hasn't been swapped out yet, it's next to be done and it should sort the problem. 3 IACV's haven't worked so ECU is next on the list.