Idle surge

[STiNGR]

I have a 99 wrx wagon, put an external gate on it and have noticed a slight idle surge. It will sit on about 800RPM then drop down to about 500-600RPM then hop back up to 800RPM. Not really to sure what the problem may be. Thinking AFM maybe?

[Swindog]

IACV

idle air control valve.

Needs a clean.

[Guest]

borrow an afm and try it. that what my foz did but didnt throw a code changed afm and was allgood. unrelated to external. is it hunting or just idling up?

[STiNGR]

 Swindog said:

IACV

idle air control valve.

Needs a clean.

Thanks, where will i find that part?

[Swindog]

Top of throttle body. Do a search on here you'll find a diagram.

[Guest]

could be split intake pipe, split vacuum hose, intake manifold gaskets, throttle body gasket, ICV and afm. most of that you can check in 30 minutes...

[madmike]

Hang on...

You now edited your first post to say you put an external gate now and now it hunts...

Go back and check your work.

[STiNGR]

 madmike said:

Hang on...

You now edited your first post to say you put an external gate now and now it hunts...

Go back and check your work.

No, I edited my 1st post because I missed out putting a "n" on the end of then. Thanks.....

[Stoffa]

+1 for Idle control valve, the v5/6 ones get really bunged up, its the 6 pin round stepper motor that sticks out the top of your throttle body, I cleaned mine out with brake cleaner as it evaporates once it dries.

failing that maybe a vacuum leak

[Swindog]

Yeah as above my second option would be looking at your lines to the wastegate but if its hunting idle rpm its NORMALLY (not always) the iacv.

[wrxguy]

Or just to be a smart ass ... SORRY!!!!

Roving Idle like a rally car!

[WRXONP]

If cleaning the iacv fails to fix it I would look at 02 sensor -when O2 signal is poor the engine will hunt for idle as the air fuel ratio swings wildly

Can test O2 simply with a multimeter with a graph

One question- does high idle work when cold ?? Is idle at cold sid and smooth ? Does it only hunt for idle when hot ? Or hot and cold ?

If cold idle is fine but hot idle is hunting that points towards O2 sensor

[STiNGR]

 WRXONP said:

If cleaning the iacv fails to fix it I would look at 02 sensor -when O2 signal is poor the engine will hunt for idle as the air fuel ratio swings wildly

Can test O2 simply with a multimeter with a graph

One question- does high idle work when cold ?? Is idle at cold sid and smooth ? Does it only hunt for idle when hot ? Or hot and cold ?

If cold idle is fine but hot idle is hunting that points towards O2 sensor

When cold it idles sweet. I just cleaned the ilde control valve, It was a bloody pig sty! Has helped but seems to struggle a wee bit, taco needle doesnt move like before I cleaned valve. Might check oxygen sensor.