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X-type v6 extremely rough idle when cold


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Hello everyone , sorry to bother you , i have an 02' x type 2.5 v6 , 5 speed manual transmission ,120.000 miles on the clock , with an extremely rough idle when the engine is cold , it sounds like it missfires alot (allthough no missfire codes stored), like running on 3 cylinders , when i try to rev it up , it's running on those "3cilynders" up to 2000 rpms , above 2000 rpms it backfires (not every time) :))) and the other cylinders start to ignite , and it runs.... "normal" if i keep it revved past 2000 rpm.

This happens for about 5 minutes when i start the car cold , after that everything starts to settle down , and it runs OK , but it lacks power on acceleration...

I have no faults stored on the ECU  , only an abs sensor on the rear left side

I have tryed :

smoke test on the intake , no leaks ; replaced the fuel pump , replaced MAF sensor , replaced MAP sensor , replaced spark plugs (gapped plugs 0.055) , replaced fuel pressure sensor 

Still haven't done a compression test , any other ideas? Anyone??...

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For who ever is interested , the problem was a busted-melted catalytic converter and a piece of it made it's way down the exhaust and blocked it

Sypmtoms got worse and worse to the point that the car would only rev up to 2000 rpm , the engine sounded really strange , then wouldn't even start.

I checked the timing , replaced both vvt solenoids , cleaned solenoid filters , replaced camshaft sensors , replaced cranckshaft sensor , replaced ignition coils , replaced spark plugs again

At a point i removed both pre-cat oxygen sensors and the car started right up , took it for a drive and she pulls better than the first day i bought it

I've gone mad trying to swort out this problem , but i am also pleased that now i know this car inside out like the back of my hand , hope the solution helps somebody else too

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