P505 error code, air intake chamber fault?
My 159 1.9 JTS has developed an odd whine and apparent misfire when idling.
On inspection, the noise seems to come from the air intake chamber at the front of the engine, and both noise and misfire disappear when you squeeze the pipe that travels from the cap on the top of the chamber into the top of the engine.
Diagnostic test throws up a P505 fault code, 'Idle air control' fault.
I've popped the cap of the top of the intake chamber and removed the orange diaphragm which looks in good condition; underneath though is coated in oil (not sure if that's normal or not)
Does anyone have any suggestions as to what the likely cause may be and how I can go about fixing it?