V50 T5 Intermittent Misfire

[viper32cm]

Greetings All,

I have a 2005 V50 T5 with about 125k miles. I'm a fairly experienced home mechanic, especially with BMWs, but my old V50 has me stumped I'm afraid.

I replaced my spark plugs last weekend with Volvo-branded plugs p/n 30751806. After replacing the plugs and putting everything back together the car started skipping as soon as I turned it over. I immediately turned the car off removed the new plugs, checked gaps, and tried again. The same thing, except the skip is turning into a full on misfire. I try several different things, including reinstalling the old plugs. The engine still misfires.

I then connect my Bluetooth OBD-II scanner. It shows an intermittent misfire on cylinders 2 and 3. I move plugs around and coils around. It doesn't make a difference. There is still a misfire on cylinders 2 and 3. Sometimes with a flashing CEL, sometimes without. Sometimes the code is of the "danger to catalyst" variety, sometimes it isn't.

Out of an abundance of caution, I purchase five new Bosch coils. I installed them today. It made no difference--misfire on cylinder 2 and 3.

With the plugs and coils ruled out. I move onto wiring and check continuity with my multi-meter. All five coil connections have strong continuity across the ground pin, the ECU pin, and the fuse box pin. Thus, it's not a problem with worn or degraded wiring.

In doing all this, something funny happened. The car got better! It's now just skips. No CEL, and while it's a little rough it's not shaking the car like it was beforehand. I've run my scanner multiple times after the car got better. It does not find any codes.

At this stage, the only remaining item on my possibilities list is the ECU. However, I don't understand how the ECU could have died or started failing in connection with a spark plug change. Has anyone encountered something like this? Does anyone have any ideas as to additional steps I can take?

[precisionguesswork]

Could be dirty, bad or failing injectors or injector wiring.

[Leo123]

I would also check the MAF sensor; if it is broken, then the fuel supply is incorrect and, as a result, misfires. and check the intake manifold and all vacuum hoses for air leaks. if you need auto parts, go to globy.com