S50 swap random intermittent multiple cylinder misfire

[Calidownhiller]

So I'm posting this for a friend. We recently finished his s50 swap into a 318is.

The car starts and runs for about 10-15 minutes perfectly, then starts missing and bogging down very badly. While sitting idling it has backfired through the intake while under light throttle.

*new parts

Specs:
S50
Red label dme
Walbro fuel pump*
Coils*
Spark plugs*
Maf*
02 sensor*

I haven't had more then one chance to try and diagnos the problem so I'm just trying to collect all the details from my buddy before I go back to his house to help him. I also was not as involved in the swap as I would have liked to have been and did not get to witness most of the install. So I'm going in sort of blind as to assume they did everything correctly.

[e30rapidic]

Santa Rosa CA? damn, I just flew back home from there.

Do you know if they messed with the timing at all?

[Calidownhiller]

Yup California. Great place.

Nothing was touched timing wise.

So when the harness was done apparently, our other friend accidentally cut off the connector for the o2 sensor. He then reattached it later. Out of a hunch I asked the owner of the car to unplug the o2 and drive it like that today. He said the car ran fine, minus a couple instances on decel, he felt like the car was decelerating harder then usual.

Could a wrong o2 or wrong wiring cause this kind of random misfire?

[golde30]

Is it throwing a check engine light?

[91s50318]

Okay so this is my car that is being discussed here. No, I am not getting a CEL when it misfires, I did get one before replacing the coils for about 2 seconds and then it would disappear. I disconnected the o2 sensor and drove for about 25 miles today without a single misfire. We have gone through and replaced coils, spark plugs, fuel pump and fuel filter and nothing helped dramatically until disconnecting the o2. I would drive for about 15 minutes perfectly and then misfire. Our question is like my friend stated above..could it be a bad o2 sensor or faulty wiring that could cause this random misfire? Again, the problem didn't occur today while I drove with it disconnected.