basically when cold or starting to warm if i hold the throttle constant the car surges or judders very slightly,can just feel it,also seems to be running rich as the backbox is very sooty,done a check and no error codes,anyone have any ideas

 

Maf Sensor by sounds of it mine was doing the same.

 

thought with the maf it runs lean and not rich?id it cure yours when you changed the maf?

 

Yeah replaced Maf everything seems fine now, used to run jerky/stuttery same as your saying. I'm not an expert but with my car being a 99 WRX i was told Maf's on them are pretty crap.

 

o2 sensor can cause a very light surge problem without throwing a cel light on

 

Is there any simple way off cleaning the MAF sensor?

 

I've got exactly the same problem on my MY01, we've swapped the MAF sensor, MAP sensor, both oxygen sensors and BOV.....but the car still does it. My engine is a brand new EJ257 shortblock with CP piston, Eagle billet rods, ported and polished heads, Deatschwerks 750cc injectors and AVO450s Turbo. I have an ECUtek equipped ECU.

The next thing to try is someone else's ECU......IT'S DRIVING ME MENTAL!!!!

 

I have the same problem, but was only after fitting a new lambda i felt it.
The lambda wasn't actually new but better than my old one as the old one failed the MOT and the 'new' one didn't.
I know my MAF isn't spot on but is much better than a broken one (i know this due to buying a right duffer off ebay!)
I suspect MAF also. As the voltage is all over the place when logged on the laptop.
Tom

 

Anyone?

 

I wonder if its the same problem Im having.....only happens when warm tho
with me the Apexi shows that the idle switch isnt actuating until the throttle position has moved from 4.83V to 4.64v (engine off and cold)

I'm susepcting the TPS/idle switch

...oh and I cleaned my MAF with brake cleaner and let it dry before putting it back together...did that quite a few miles ago and all was well

 

Was also thinking, could a faulty/corroded coolant temp sensor be a problem with results like this?
Just a guess.
Tom

 

from experience of quite a few club members having the same problem, boost control solenoid is the cause