Finished my engine swap and then...

[series88]

So I finally finished my engine swap. It's a same engine swap. My old engine was just kind of toast. So now that the new motor is in, it fires up but after about 5-10mins of idling, it starts getting rough and bugs down. When I turn the engine off and start it again, it will run fine for the same amount of time.

Any ideas?

[bmwman91]

Did you remember to reconnect your O2 sensor? How about the coolant temp sensors in the head? It sounds like the car is warming up and entering closed-loop operation mode. Some sensor that is ignored during warm-up is probably not connected and making the car mad once warmed up. Does your check engine light come on (and does it WORK)?

[series88]

Yeah, as far as I remember, all sensors are connected. O2 and temp sensors are all plugged in. And yes, the CEL does turn on when its misfiring like crazy and about to die. but when gas is applied or the car is restarted, CEL is off again.

[bmwman91]

That really sounds like a vacuum leak. Check the vacuum hoses under the throttle body for cracks, it is super common.

Also, did you replace the intake boot? New ones don't come with this plastic plug thing and have a big opening on the bottom side.

[Threehz]

That really sounds like a vacuum leak. Check the vacuum hoses under the throttle body for cracks, it is super common.

Also, did you replace the intake boot? New ones don't come with this plastic plug thing and have a big opening on the bottom side.

So true. A little vacuum leak can wreak havoc. Did you check and see what code the CEL is throwing?

[series88]

So true. A little vacuum leak can wreak havoc. Did you check and see what code the CEL is throwing?

Didnt get to check on CEL. It turns off before I can even get it scanned.