Hi guys, at first I would like to wish merry christmas to all members of this great forum and community
I have here another issue with my 166 3.0 99" where I am not 100% sure what could be the fault source. The car mileage is currently 130 000 KM so approx. 80 000 miles.
My car is decated with a stainless steel pipe very very similar to the alfaholics GTV6 3.0 decat pipe :
View image: decat pipe.jpg
The issue with the car is that time to time I have rough idling and I can't find out what is the reason. The idling engine revs are according to the first look stable(~680rpm), but from time to time the idling is pretty rough and seems to be missfiring and running only on 5 cilinders but the revs are still relative stable on 700rpm. This is mostly happening when the engine is warmed up to the working temperarature 90degrees and I am eg. driving in the city and currently waiting on the traffic light or just stuck in the traffic jam. The engine suddenly starts making medium vibrations for 10-30seconds but then it disappears and it is idling fine again. As I told this idling issue is mostly happening when the engine is warmed up but time to time it also happens at the morning after cold start and sometimes also in the summer after starting warm engine. The misfire always takes only several seconds and then disappears. During the misfiring the revs are pretty stable somewhere between 650-700rpm.
I was TWICE with the car in the garage on the diagnostics and there were no errors shown, MAF and O2 sensor were both giving proper vaules during idling and also during 2000/4000/6000rpm, no errors with coil packs or spark plug were shown, all sensors seemed working fine.
I have recently 6000miles ago changed the O2 sensor (BOSCH) and the sparkplugs (original NGK platinum) are 20k miles old so there I think should not be a problem. Air filter was changed recently couple of miles ago.
I have also several times performed the ECU reset - no affect on the rough idle, only the typical symptoms as improved fuel consumption and throttle response etc.
Before I was on the diagnostics, I was thinking that this could be supposed only by failing maf, but the guy which was performing me the diag told me, that the maf is according to his opinion giving correct values and the maf seems OK for sure. He also said that if the MAF would be really wrong, the issue will be reoccuring more frequently if not constantly. That I think can be true because I am sensing this behaviour of the car for the last 10000 miles and it is still the same.... The MAF is original BOSCH 0280217531 for alfa CF2 V6 engines and was changed before 4-5years / 20-30k miles.
When I informed the guy that the car is decated with the mentioned pipe, he told me that this could be the weakpoint as the O2 sensor may time to time (when the subjective engine misfiring / vibrations is currently occuring) receive wrong values as there is no backpressure due to missing CAT.
I have the CF2 version of the engine, so there is only one O2 sensor which is mounted in the decat pipe as shown on the screen of the above.
Two things that I now suspect are MAF (also due to fact that the values on the diagnostics were shown as correct) and the mentioned decat pipe which I have installed in my car.
At first I thought it could be also failed coil pack but as I heard, coil pack issues are everytime shown on diagnostics....
I can only guess if the missfiring can be due to the fact that the car is decatted because when I bought the car, the CAT was already near to death if not death and as I remember, the time to time vibrations / misfiring were at that time already present.
But I know about plenty of cars (bimmer E39 540i, bimmer E36 320i, AR 156 2.0TS...) which are decated and they are running and idling pretty normal.
Therefore I would like to ask you for help. I have already searched on this forum but did not find anything similar
Thanks in advance.