Hi people,

I have been experiencing an odd issue with my 04 build MY05 STi.

It seems to jerk a little bit when you are cruising at constant speed and you can see the tacho bounce a bit, it seems to be worse in hot weather and when the aircon is switched on but still does it without the aircon.

Also, most of the time it will idle fine, but once again it will occasionally hint for idle and today it even stalled cos the idle went to low.. ONce again this is worse when the aircon is on but it still does it when it is off..

I am thinking AFM and a mate suggested poor fuel and my mechanic said that idle speed may need to be increased - that said the idle speed my do something for the idle hunt but I do not think it will fix the jerking - which mind you is not huge jerks, but enough that you can feel them. Last time I had it in at the mechanic he plugged the diags into it and it did not throw any codes.. So I am looking for insight as to what it can be.

The car has no mods besides a diff back exhaust and tein's.

Thanks in advance.

This sounds similar to my Problem on an MY00 WRX.

Mine is intermittent and I thought I had a win By changing the IACV but it's still Happening.

Still troubleshooting when I have the Time.

I hope you find the solution and It helps my cause

Good Luck

sounds like a vacumm leak from somewhere, and it seals up some of the time. check all vacumm hoses, especially the one to the bov, and check the hoses from the top mount to the turbo and manifold and bov. make sure all hose clamps are tight. If all good, clean the afm out with a bit of throttle body cleaner or what ever, see if that works if not maybe a carbon clean might help. my work does them, but were flat out until after the new year.

Thanks for the input. I will check the AFM and see if it is dirty - if it is I will replace it as I have read that just simply cleaning it may make the car appear to run better but it may still not be good. The vacuum leaks are something I did not think of - I take it a service manual will be able to give me a rundown of all the vacuum pipes I would need to check?

The symptoms are definitely worse in hotter weather.. However - there was one mod I forgot to mention and that was a GFB hybrid BOV that the previous owner installed. The other day, I adjusted the spring rate to a lower one and checked the piping, after doing this, it seemed to run better - however our days have not been as hot.

I am running the BOV in plum-back mode (I hate atmo venting) but is it possible that the BOV could be causing these symptoms?

The AFM did not seem overly dirty - but I know that means nothing..