Evening all, desperate for help with my 1998 996 c4 cab,,ok so the car has been in a garage for 5 months , started with ims change That was completed ! Then came the issues , the car would not start or infact do anything basically the immobiliser would not let anything happen , new immobiliser same problem so they changed the ecu , done problem solved everything as it should apart from it was running lumpy Occasionally , turned out to be a valve under the rocker cover (excuse my ignorance ) that was changed . Car has had full plugs coil packs oil change , smoke tests , fuel pump test everything has come back correct , starts ok but as soon as it gets warm it runs like it has had diesel poured into it, my mechanic now believes that the ecu we fitted is possibly from a 996 with 4 exhaust sensors not 2 like mine !!!! Can anyone confirm this would cause this ???? Please desperate just want my car back for the summer , thanks in advance .. den

No none !!! It had misfire on cylinder 6 last year but coil pack 6 was split in half , fine since then

Yes they have done a good few previous to mine !! Starts and sounds nice runs smooth , and then as soon as it gets even a bit warm bogs down . No smoke , no strange noises , no lights

This is what he is thinking , but on research they all seem to have the same part numbers on a few different kinds as it’s an early 1998 I think they updated every 2 years , my mech has spoke with another couple of Porsche specialists that he has had ties with in the past and no one seems to be able to confirm . Also called a few specialist breakers and they were unaware there was a difference

Sorry I did reply not sure where it disappeared to !!! It seems most Porsche mechs or breakers didn’t seem to know if there was a difference between the ecus but it seems there were a fair few !! And it seems the chances of getting the exact one we need gurenteed from somebody is a bit hit and hope ! With all this said and done , with new coil packs, new plugs, new (egr valve I think) , new idle control valve, new plug tubes as was a air leak, now smoke tested , no codes , what else could cause such drastic engine bogging down and hunting when mechanically things seem ok, as I said previous no smoke or lights , just bogging down once warm

Fuel pressure is fine and the coil packs were split so needed changing , plugs were due also . The valve was also failing , and immobiliser had a random not starting issue , all these things were due to be changed to be fair as the car had been sat for a couple of years . From what my mech is saying it’s occasional and will sit sometimes and run smooth as ,then out of the blue bog down

I’ll mention it to him tomorrow. He also mentioned that it was hunting when I last spoke to him ! I’m just hoping for a quick fix to be honest I’d pay anything at the moment to get it back healthy , driving me insane and him I believe

Yes bill uk ?? That obvious ha ha . Just seems so many dead ends and so many possibility’s which is difficult when not throwing any codes or cel lights . Air tested which rules that out .most things have been ruled out , im no mechanic but I am an engineer so understand how things work . But baffled by this as is my mech