JLH96

Hey mate I've got the same problem with my 02 B4 no resolution yet but hopefully someone suggests something here


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If its an oiled K&N (I think they all are), you've dun-goofed. It needs to be the dry unwashable type. Genuine is the best and flows just fine, or STi, it takes the same size as WRX I believe. I've used a Cosworth before too. You'll have to clean the MAF with CRC Mass Air Flow Sensor Cleaner if you've used an oiled filter - do not touch the MAF element, just follow the instructions on the can.
 
Catback (after the cat) shouldn't require a re-tune. But if the cat was changed for a higher flowing one, it would need a re-tune.
 
Yes resetting the ECU just involves disconnecting the battery for 10-15min. If your car has the Brant alarm still, this can be problematic as the code may reset - but it should be fine. 

Unfortunately it is an oiled one [emoji30]

Thanks for the advice mate


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could be two things.
 
rough idle sounds like a spark issue -- fouled plugs or failing coilpack?  Either that, or idle speed too low - usually a gummed up IACV. Take off your intercooler and give it a blast of UEC. Wouldn't suggest removing it unless you have new gaskets handy.
 
Is the 4500rpm problem also a result of misfire?

Okay thanks matte I'll give that a try I'm hoping it's just sparks for rough idle.

No the 4500rpm started after I got my catback put on


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It wont rev past 3500/4500 if it detects excess load or knock. Until the ecu picks up everything is ok again and it perks up. That condition has happened to me with a clogged air filter on the highway one time, no check engine light either. It might need an ecu reset? But if its idling rough, it might be a prick to get it out of limp mode. Its just the ecu protecting the engine from another underlying issue.

I've just replaced air filter with K&N high flow so not too sure about that mate. Does a ecu reset just involve disconnecting the battery?


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Okay cheers guys, if you know anyone selling one would be swell if you could point me in that direction


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