Unstable Idle

[wirdy]

Any ideas?
From cold, just about ticks over (does the 2.0 CT have a cold start solenoid / valve?).
When warm will drop to about 500 rpm and just about stall / tick over, then slowly cranks up the revs in steps about every 10 seconds until it reaches a normal idle after about 40 secsand 4 of these audible steps.

Idle is then stable until the throttle is blipped and the cycle begins again.

ECU?

[noz]

Hi wirdy,

Sounds like your idle air control valve is sticking. This is a valve which allows air to bypass the throttle and is under the control of the ecu. The movement of the valve allows the ecu to control tickover speed. When the engine is cold then the valve shoud be further open. As the engine warms up the valve should slowly close to its normal operating position. Instead of moving slowly and precisely it's movement is sticky and it moves i jerks once theres enough force from the motor to overcome the high friction. This appears to be a common fault on the 2.0. However, its easy to fix. Remove the valve and thoroughly clean. That's usually enough to get it going again.

Cheers

noz

[wirdy]

Ta Noz, sounds likely. I need to take the whole induction system apart anyway to give it all a good clean. This might explain the lack of 'go' off-boost that I'm experiencing with this new acquisition.

Remind me never to get another car of the exact same engine / gearbox type. It gives far too much scope for comparing and getting paranoid about the differences.

[Ciaran]

Sorry to sound daft, but does the 2.0i have a similar valve? I'm also experiencing this kind of behaviour, low, rough idle, and will sometimes stall if braking harshly from say 50mph to a standstill (if lights change suddenly and the like). Seems to get worse as the weather gets warmer too...

May be a completely different issue, but thought I'd check rather than opening a duplicate thread.

Ciarán

[dean]

Hi Ciaran

Mine definitely has, its on the inlet manifold with a 30mm dia hose running from it to the inlet ducting (to bypass the throttle housing) but its a Bosch motronic 5.1 E.M.S, i dont recall seeing one on magneti marelli but i could be wrong, its been a while since i played with one of those.

Dean

[wirdy]

I'm presuming I took the correct thing off and cleaned it - it had a bosch label on and a single plug on the rear. Once off it has a sleeve valve that opens and closes as the centre shaft rotates under control of a motor.

Tried running the engine without it fitted and you get a huge pressure of air out of the inlet pipe (from the free running turbo?) and the engine immediately revs to 2000rpm.

Bit of a bugger to clean though and it's still feels gritty when hand rotated. Have tried degreaser and white spirit. Looks like I may have to pinch one off my spare 16v if it's the same type.

[Ciaran]

Ta Dean, will give it a look over this weekend, will start a new thread if there's any developments

Cheers

Ciarán

[dean]

Hi wirdy, yeah you have the right one. Dont forget yours is a turbo and ciaran and i have n/a's so the layout of the inlet piping is totaly different. D