frustrating volvo idle

[Dmorgan]

iv owned a 1995 volvo 440 1.8 b18u for the last 2 years but the last twelve months its idle has become very iregular 9 out of 10 times you drive it its fine then for no reason the idle will become high and revs will stay high when changing gear sticking at anything from 2000 to 4000 revs these revs will go down but very slowly this will go on for a couple of days and then be ok again for a couple of weeks and so on.
iv replaced the stepper motor and flywheel sensor and checked all the air pipes and there fine theres no faults stored on the diagnostics the car looks and drives great but this problem is really getting to me
Does anyone know if this could be temp sensor or ecu problem but i thought these would be logged on diagnostics

[NI_Volvo_Nut]

It was the stepper motor on mine, if you disconnect it, it will run like nothing when cold, but will idle perfectly and drive perfectly after a couple of minutes, also when its reving high, try unplugging it, seemed to bring the idle down after a couple of revs once disconnected.

[Baffler]

More than likely the stepper motor or technically known as the idle speed control valve. These clog up with carbon and are difficult to clean. Did you put a new one on or was it second hand?

[Paul240480]

Hi, try this for cleaning the Idle Control Valve:

http://volvo480.dragons.org.uk/forum/viewtopic.php?t=15569

The very last post on this thread is from me, with a link to another post on a very similar problem, this also has some useful info.

Took me nearly two years to solve mine & I'm still almost expecting the problem to re-appear as it's only a short time since the last attempt at a fix

[Paul240480]

Another place to check is the pipes to the carbon cannister in the front off-side wing. (Not sure if this is turbo's only?).

Remove off-side day-run-light/ indicator & shine a torch in through the 'hole'. You'll see a number of thin braided hoses. Using the torch & a long screw-driver give the pipes a 'wiggle' to see if they have perished. If they are 'holed' they too can cause erratic idle symptoms. Mine were luckily okay. Not sure how you get to them if they need replacing. And also as I mentioned these pipes may only appear on turbo models?