Erratic idle

[D813YBB]

My car has suddenly developed an erratic idle with the revs rising and falling. This is leading to some interesting manoeuvres when approaching roundabouts and junctions with the intention of slowing, when the car suddenly powers ahead!

The temperature gauge is also falling back down the scale when cruising, instead of staying rock solid just below the half way mark. I cured that once before by changing the themostat about a year and a half ago. Could the two problems be related?

TIA

[ChrisM]

Oops, thought the title was Eric Idle... :o

My car does this, I think it's something to do with the autochoke. Try unplugging your ECU and cleaning the contacts...

[E_T_V]

The ECU you need to unplug and plug back in to clean up the contacts several times is the one in the glovebox roof (the autochoke ECU), rather than the igntion ECU.
If that doesn't cure the problem then I'd change the thermostat just in case. If the idle speed increases as the gauge reads cold then that is "normal". If the gauge going cold co-incides with travelling at speed and the engine warms up to normal temperature when stationary then that indicates a thermostat fault.

[E_T_V]

Actually thinking about it if it is the early style dash then the ECU is tucked up behind the dash on sort of where the drivers knee sits. There are two small black screws holding it to the dash. If it is the late dash then it'll be in the glovebox roof.

[Chris Y]

Yeah, the 'fuel' ECU can be the cause of many an Eric Idle. Maria's Hexie had a serious case of the boy racer traffic-light revs once, which was caused by a failing fuel ECU!.