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Help!! Rough when cold


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Ok so recently done a lot of suspension work. Had full coolant flush and new radiator. Had new oil 10w40 millers cfs. New platinum plugs. New crank seal, oil separator plate, rocker gaskets. Oil filter. Fuel filter. Recently swapped to v power fuel instead of 97 supreme. Previous oil was 5w30.

Had the car for 4 weeks and was super. Since it had new seals, gaskets, plugs, oil change and swap to v power, the engine runs stupidly rough when started cold.

Slight throttle makes revs go down, hesitates and then goes up. Backfires on more throttle. Idles lumpy and almost stalls. Searches for idle. When warmed up, runs absolutely fine with no troubles and idles fine.

Car is 95 import wrx. Was fine up until service. Ive tried cleaning maf. I know the o2 sensor is faulty but been faulty since i had it. Got a new one to go in but struggling getting old one out at the mo.

Its been fine until it was serviced and changed fuel. Could the oil make a difference?

Also was fine for a couple days after it was serviced and swapped fuel.

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Did you do an ecu reset ? It takes a while for it to 're learn ' the fuel so could be that, just plug the black and green diagnostic wires in then go for a gentle drive until the cel light flashes constantly. Unplug then drive,

Could all be down to the O2 sensor as it will be overcompensating on cold start over fueling until warm.

You need a 22mm open ended spanner to get the O2 sensor off access is a bit tight

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I cant find the green plugs. I can find the black ones. Plug them in and the anti lock brakes comes on but cant find the green ones yet. Can i ecu reset by disconnecting Battery?

And i know how to change the o2 sensor but the bugger is proper seized! Lol

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