I have a 2006 XC-90 Ocean Race Edition with a very vexing fault code problem. It began first with a miss developing at cruising speed accompanied by a warning “slow down or shift up", and flashing amber exclamation triangle displayed on the message screen.

Putting trans in manual mode & down shifting made it drivable.

PO300 Codes were indicating random misfiring in almost all cylinders.

So far I have replaced; All cam position sensors; Crank position sensor; VVT solenoids; Both bank two O2 sensors

Recent installation of all new ignition coils seems to have made things worse and now in addition to the misfiring codes, this codes appears:

PO506 (Idle Control System RPM- Lower Than Expected)

Cold engine idles very rough for a few minutes then smoothes out & idles normally. TD

 

so it sounds like the idle control system is introducing an air leak causing the car to run lean and subquently things heat up and you get misfires. the P0300 is saying you have misfires that are not cylinder specific which rules out, plugs/coils etc so the next thing a tech would triage is things that can impact fuel mixture. That could also include a wonky ECT sensor so that may be a good thing to test first.

 

Good suggestion. I'll post what that might accomplish. Thanks, TD

 

By ECT sensor are you referring to Engine Coolant Temp sensor? I'm not experiencing any engine or coolant temp issues so how could that be causing cylinder misfire codes? I thought maybe you meant ETC, Electronic Throttle Control? TD