I have a version 5 Type R with the following symptoms:

• Runs perfectly fine when engine cold
• Once up to temperature and come to a stop the idle speed is dropping 800~500
• Accelerates fine but during deceleration the check engine light comes on. If I dip the clutch to let it drop to idle speed the light goes out but idle speed not stable

I have read fault code and it comes up with IACV, not sure on exact code now but I know that the MAF is a common fault and can cause this sort of problem. I would have just went ahead and got an IACV but it actually looks new. I did give it a quick clean but no different.
Not had the car long so expecting the previous owner tried changing it and gave up when the problem persisted.

Anyway, does this sound familiar to anyone?
Only mod is a 3" exhaust system

 

I'm not sure if this applies to you being the V5 which I assume has OBD? A full reset on the ECU might just sort it out. Certainly did on my V3 when I had all sorts of stall/idle problems but it's not OBD.

 

I would be surprised if that is all it needs but definitely worth a try

 

It really is worth a shot. My car was un-driveable, even stalled a few times going through MOT! I had to drive 5 miles home at 20mph with serious misfires and stalling at every red light. Once I found out about the ECU reset and actually did it, my car has been 100% for over a year. Is there a chance your IACV was replaced and the ECU wasn't cleared?

 

No luck but once the reset was complete code 41 was shown.
41. Air/Fuel Adaptive Control

Sounds more of a MAF problem to me, can anyone confirm?

 

Could be a lambda sensor too I suppose. Can you borrow a known good MAF and lambda to try?

 

Well I tried another MAF and IACV but no change.
I checked the fault codes again and it gave two relating to the O2 sensor. 32 and 41.

I've got an O2 sensor from local motor factors. Part no: VE381263. As they don't list import parts and they had 2 possible matches only one of them had the same plug. is part number same on uk models?

Anyway after a short drive the car did seem better without idle speed dropping but the CEL is still coming on although at a different point. It's now as I go back onto accelerator.

Checked codes again and back to 24 idle control

Any ideas?
Is there anyone in the north east that can plug in and see exactly what is going on?

 

i have a v3 wrx have same prob cant figure it out at all changed lamda o2 sensor and maf still the same let me if you get to the bottom of it i checked everything twice and im still scratching my head

rob

 

No problem. Will do.
I'm thinking an air leak could be possible. As it only seems to come on under deceleration I'm thinking a vaccume hose could be collapsing with the vaccume pressure. I will try changing all the smaller hoses with silicone.
They all seem very hard and brittle so silicone may make things worse. Hopefully one of them is cracked or split

 

That's what I'm thinking that there maybe an air leak I also changed the temp sensor too as I was told that could be an issue got to be pulling air in after the maf as I'm running out of ideas

 

I know it's a bit late but thought I would update.
I ended up taking the car to alyn at AS performance and the idle problem was down to an exhaust leak in downpipe. The car now idles perfectly.

The engine light may be unrelated as it does still come on now and then when decelerating but hopefully this isn't anything serious. I didn't reset the ecu so I will try that. Fingers crossed