I finally finished the engine swap in the $600 Volvo. Yes, it runs. However, I’ve been ripping my hair out for the last 2 days trying to figure out why it idles like shit.

When the car is cold and I fire it up, it will run and idle fine for a few minutes until it warms up a little. Then it starts to idle like crap. Basically feels like a random misfire. If I hold the gas pedal at around 1000 rpm it idles fine. Driving also feels fine until I start to coast and the rpms drop to idle.

Check engine light is not illuminated and there are no codes.

So far I’ve tried to replace MAP sensor, air temp sensor, coolant temp sensor, TCV, cleaned and then replaced ETM with another one. Checked compression - 135psi on all cylinders. Replaced spark plugs. Replaced fuel filter. Got another ignition coil and tried swapping one at a time to isolate it - no change. I did notice that the coils have hairline cracks on them. Checked all vacuum hoses, checked fuses.


Next I was gonna order 5 new coils and replace them all to rule them out. Otherwise I am running out of ideas. Could flaky crank or cam sensors act this way? What about VVT solenoid? Unplugging the solenoid doesn’t seem to have any effect.

I want to start driving it but this issue is holding me back from getting it plated.