Just wondering what could be wrong. When in drive the car drops down to about 450RPM. Same applies to Reverse. This only happens when brake is applied or car is slowly rolling. Feels like its about to stall :shock:. Also car is due for service but I doubt this would affect it....

The car only got a brand new transmission less then 1 year ago.

I'd say that either your idle speed controller is faulty, or your idle bypass screw is adjusted too far. What speed is the motor running at in neutral or park?

Running at normal, 1000-1500

Was fiddling around near the foot weel putting cross overs in, could this have done anything.

Is that on a hot or cold motor?

I wouldn't think the crossovers would have done anything, unless you've accidentaly grounded the ISC wiring somewhere along the way.

Doesn't do it whilst cold, only hot.

Was recommended to get a new O2 sensor :cry: , how much are these roughly and is there any way of testing?

If you're getting rotten fuel economy (20+L/100km) from sedate driving, a new one is in order.

They're quite expensive from Mitsubishi, but my brother picked up a Denso from America for $96AU.

Was recommended to get a new O2 sensor :cry: , how much are these roughly and is there any way of testing?

Problems with the ISC won't be related to oxygen sensors. If anything, check the coolant temperature sensors and connectors to ensure they are ok, since you mention it's temperature related. Also as others have suggested, you may have to readjust the idle correctly, and ensure the throttle and ISC valve aren't blocked with carbon buildup or oil.

To test the oxygen sensors you could check the codes on the ECU to see if they are appearing there, although I wouldn't trust this alone. To test it properly you normally need either a graphical multimeter or oscilloscope to test, as they rapidly oscillate if operating correctly making standard multimeters useless in such a situation. As the third gens use a heated oxygen sensor, they tend to be a fair bit more expensive than the older single-wire type, generally above $100 each last time I checked.

NRMA looked at it, was the timing belt, as I was thinking this morning when I heard the sound of a belt of some type. Immediately thought timing belt :rant: