Got a XC90 2.5T 2004. It runs really well the first minute but it’s idling rough when it’s getting warm. Some misfiring every now and then.
I’ve changed throttle body, MAF and fuel filter. I’ve cleaned and checked the two vvt-solenoids. Checked for leakage… Still the same behavior…

Any suggestions?

Spark plugs? We’re changed in march but to cheaper ones. Wondering about getting Volvo ones…

Intake air sensor shows about 65F (before start) but the ambient temperature were 36. Can that difference cause the rough idle and misfiring?

crank shaft angle sensor?
camshaft angle sensors?
anything else? O2?

 

Did you test the engine coolant temp sensor? I'd also test the air temp sensor resistance and consider cleaning contacts/inspecting wiring and testing ground points. The difference between 65F and 32F on a temp sensor is like 2000 ohms so I'd think it could make a difference. If the cam position were off due to the VVT, I'd expect a fault code. As to spark plugs and coils - going back to genuine Volvo which come pre-gapped is an easy change. Are the misfires generating fault codes and if so, which cylinder? I'd also check out the wire harness/connectors to the coil packs. Finally, did you measure fuel pressure? Not sure if your year uses a regulator or a pressure sensor (Volvo started moving to the pressure sensor/variable volume pump in about 2004/5 but that may be worth looking into. As to O2 sensors - have you looked at run time data for fuel trim or see a fault code? Usually intake air leaks are the number one cause (and the codes point to the O2 sensor) so you may need to have a smoke test done in case there's a leak in a hard ot spot place...

 

Codes? That would be a good first step.And a good scan tool can view live data and check most components (rather than replacing stuff randomly)

 

I've checked the coolant temp sensor, it seems to work fine.

Actually I had codes after a test drive. I took about 20 miles driving til 261A and 262A Long Term fuel trim, popped up. No other codes.

Next step will be to change the spark plugs and to clean and measure the resistans in the MAP sensor (combine pressure and temp).
I can't measure the fuel pressure or do the smoke test by myself, but I'll take care of that next week.