Cam pulley can only fit one way (although probably wouldn't stop some people from trying lol)
Chains can and do stretch but it would have to be on its last legs to move it out enough to throw a code... never seen it before but who knows
Pattern tensioners vary immensely... I use a GSF one as its half the price of an OE one... but GSF supply whatever they get their hands on... I think I was lucky but have seen a few GSF ones fail... they look different to the one I used so different supplier different rubbish..
I still think there is something not put back together correctly... if it was fine before and all thats been done is two valves changed then my money is on an assembly error in the head...
I sure hope they put the cam caps back on in the right order too...
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