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[hairydavid]

Help!
My 1999 2.5 V6 CDX Manual has developed a regular problem with the idle speed. Usually after a short journey in to town and especially during a multi-stop trip into town, when I have to stop (e.g. at traffic lights or when parking) the idle speed increases from the 'normal' 500rpm to in excess of 3000rpm.
The only way to pull away (when the lights go green) is to put your foot on the gas to about 5000rpm and pull away slowly on the clutch. If you don't, it stalls and then its a heck of a job to start. If you turn off the engine when it's reving at 3000rpm it is a heck of a job to start unless you leave it for at least an hour.
If you can just sit there at a standstill, the idle speed goes down to below 1000rpm after about 5 minutes but that's not really practical at traffic lights!!!, so the only practical 'cure' is to flip the bonnet and unplug the Idle Control Valve (then plug it back in again). The car then behaves ok until the next journey.
The problem also occurs (but less often) when I pull off the motorway after my 30 mile drive to work, although it sometimes judders when you put your foot on the gas at lower speeds.
I have changed the idle control valve (twice), put the car into a 'Vauxhall specialist' garage who fixed some leaks in the vacuum system (made no difference) and who put a new throttle control switch in (made no difference).
I have no idea what to try next. This is my fourth Omega - I really like this CDX and really want to hang on to it, but it's starting to drive me nuts.

[zirk]

Sounds like the ICV needs a good clean, and clean breathers whilst there. 

[henryd]

Do the paper clip test and post the codes found would be a good place to start

http://www.omegaowners.com/forum/index.php?topic=90581.0

[zirk]

Do the paper clip test and post the codes found would be a good place to start

http://www.omegaowners.com/forum/index.php?topic=90581.0

Yep, good point Henry, skip read the post and didn't see the ICV already replaced,  , starting to think MAF know. 

[dbug]

As said read codes.

As a diagnostic, try it with maf disconnected (just unclip elecric plug)

If no different, I'd suspect a dodgy crank sensor

[hairydavid]

Thanks guys,
Not sure what 'read the codes' means (sorry, I'm a Haynes 'one spanner' mechanic!) but I'm not getting any warning lights on the dash and I'm not getting any warning messages on the computer screen (except a false 'BRAKE PAD' warning that's been there since I bought the car (brakes are fine), and the 'CHECK' indicator is always illuminated).
As suggested, I'll disconnect the MAF sensor before I go home and see what happens.

[henryd]

Thanks guys,
Not sure what 'read the codes' means (sorry, I'm a Haynes 'one spanner' mechanic!) but I'm not getting any warning lights on the dash and I'm not getting any warning messages on the computer screen (except a false 'BRAKE PAD' warning that's been there since I bought the car (brakes are fine), and the 'CHECK' indicator is always illuminated).
As suggested, I'll disconnect the MAF sensor before I go home and see what happens.

Follow the link I posted,it will show you how to get the engine fault codes with a paper clip

[hairydavid]

Thanks Henryd, I didn't notice the link earlier. I'll try it when I get home

[hairydavid]

Yo - result!!!
I did the paperclip test (this is truly wonderful - why didn't the two garages I've put the car into to sort this problem know about it???) and got the following:

57   Idle Air Control Voltage Low

I then tried unplugging the MAF and doing the sort of trip I know would cause the problem - results inconclusive: still wanted to surge to 2000rpm or 3000rpm but went down to normal much more quickly (20 seconds).

Where do I go from here? - the code 57 seems to isolate the problem to the ICV process.
Thanks for your A1 help, I feel I'm getting somewhere for the first time   

[Field Marshal Dr. Opti]

Help!
My 1999 2.5 V6 CDX Manual has developed a regular problem with the idle speed. Usually after a short journey in to town and especially during a multi-stop trip into town, when I have to stop (e.g. at traffic lights or when parking) the idle speed increases from the 'normal' 500rpm to in excess of 3000rpm.
The only way to pull away (when the lights go green) is to put your foot on the gas to about 5000rpm and pull away slowly on the clutch. If you don't, it stalls and then its a heck of a job to start. If you turn off the engine when it's reving at 3000rpm it is a heck of a job to start unless you leave it for at least an hour.
If you can just sit there at a standstill, the idle speed goes down to below 1000rpm after about 5 minutes but that's not really practical at traffic lights!!!, so the only practical 'cure' is to flip the bonnet and unplug the Idle Control Valve (then plug it back in again). The car then behaves ok until the next journey.
The problem also occurs (but less often) when I pull off the motorway after my 30 mile drive to work, although it sometimes judders when you put your foot on the gas at lower speeds.
I have changed the idle control valve (twice), put the car into a 'Vauxhall specialist' garage who fixed some leaks in the vacuum system (made no difference) and who put a new throttle control switch in (made no difference).
I have no idea what to try next. This is my fourth Omega - I really like this CDX and really want to hang on to it, but it's starting to drive me nuts.

The professionals.....or are they?....

[symes]

bet your problem is Idle Control valve is not located properly