Idle issues - V3 STI - MAF swapped, IACV cleaned!!!

[Guest]

Hi guys,

Im having some issues with my V3 STI. When the engine gets warm, the idle starts to hunt only on deceleration.

Say ive had the engine running for about 10 mins from a cold start and i get the revs to around 3000 rpm and let go of the pedal, revs will drop down to 800rpm and then go up to 1200 and then keep hunting.

If i turn the engine off and restart it will idle normally until i rev it up and let go of the pedal. Only seems to do it on deceleration.

If the engine is cold and i rev it up, it wont hunt and only does it when the engine is hot.

There are no fault codes and i have swapped the MAF with a known working unit.

I have also cleaned out the IACV and components.

[Koom]

Leaky BOV??

Or vacuum leak somewhere.

[Guest sleeperfoz]

yep i agree there koom^^^^

leaky bov especially aftermarket one,s.

or a vac line,or small split on the intake system under the manifold

[Guest]

Thanks guys. I have a GFB bov. I'll try and swap it over with another one and see if the problem goes away

Also, whats the most common place for vacuum leaks?

[Guest]

what is the manifold vac reading?

[Guest]

have you run a diag check?

Also measure O2 sensor output

[Guest]

I have run a diagnostic check but there are no fault codes.

Also i have removed the oxygen sensor since i was using avgas but i'll reconnect it and see how it goes. It was running ok for a few months without the sensor.

Thanks.

[Guest]

Yeah, but system simulates at reading 0.30v (lean) with sensor disconnected

Hence A/F correction richens the mixture

So your engine will be running RICH at idle and cruise (full throttle OK because O2 ignored at this time)

Refit sensor carry out clear memory proceedure (Iknow you have no codes, but this will reset A/F and knock corrections to zero)

Let me know

[Guest]

Thanks buddy. I'll give it a go tonite.