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Need help with Passat B5.5 02 model - no CEL, checked everything still misfiring

661 Views 1 Reply 2 Participants Last post by  2cheap4dealer
Hello all,

I have a passat b5.5 1.8T '02 model ABT spec. It has 121k kms on the clock and she has been running fine since I bought her at 98k. The problem I am having currently is that at idle it is misfiring. Consumption has also gone up; normally at idle the dash shows 0.8 l/h but now it wont go below 1.0 l/h (fluctuates between 1.0 and 1.4). On the h/way the gears change smoothly though consumption is still higher, e.g. when cruising I'd normally get 6.6l/ 100 km but now I get about 7.5l/100 km. I have no CEL. This is what I've done so far:

1. Did a check and found 2 igniters weren't firing and changed them. At that point it was horrible; running rich and stalling in traffic. Consumption was literally triple the norm. After changing the igniters the car started running smoothly. I also changed all the spark plugs at this point.

2. A few days later the misfire was back; still no CEL. Went and had it checked and mechanic said there was a problem with the no 1 igniter as the miss appeared to be coming from there; I wasn't convinced as I had bought a new igniter and plug. I sought a second opinion.

3. Next mech said the problem was with the oxygen sensors and there was nothing wrong with the igniters or plugs. I have never changed either of these sensors since I bought the car but I expected that if there was something wrong with them then the CEL would come on right?

4. So I took them out and cleaned them, together with the MAF sensor for good measure.

5. Still have the misfire, and the car shakes/vibrates when at idle (almost as if its starved). The rpm at idle is normal and not erractic (doesn't swing either way).

I'd really appreciate on any other place I should look or anybody with some pointers as to what is going on. Like I mentioned earlier there is no CEL and even though the exhaust isn't blowing black smoke anymore (now looks grey residue) I still detect smell of petrol like its still burning rich. Also the fact that the rpm is steady at idle and not erratic while still having a misfire is baffling.:banghead:

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When I had a similar issue, I also never got a CEL-the dealership told me later that it was running too rich. Mine was resolved by replacing the MAF sensor (you can test it if you have access to a VCDS cable). Even though you don't have the light on, it might be worth your while to check the other things on the Ross-Tech site that they list as being causes for running too rich:
17547/P1139/004409 - Ross-Tech Wiki

The second link is additive, so I would check that one first since your problems are when at an idle.
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