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[cavman]

Hi!
     During the recent hot weather my petrol omega 2.5 CDX (1998) has often stalled when slowing down for a roundabout or tuning a corner, which is scary as I of course loose power steering and the brake servo….

I’ve replaced the Idle Control Value but this has not fixed the problem. The problem does not occur when the engine is warming up or when the air temperature is under about 25 Celsius, I need to drive to Bavaria in a few weeks where the temperature is often above 25 C  so I’m keen to get to the bottom of this soon. I’ve not made any changes to the car recently and not noticed any other strange behavior.

Any idea what could be causing this?

Cheers.

[tunnie]

its worth doing a paper clip test and see what codes you get back 

[TheBoy]

When idling, are the revs smooth and steady, and at what rpm?

[cavman]

The Engine idles about 900 RPM (air con on).
When idling the RPM needle can dance about, dipping down to around 500 momentarily then surging up to 1300, then back down to 500, it may do this a few times before undershooting 500 and stalling. 

I did the pin test and got code 73 (Mass Air Flow Sensor Voltage Low)

[Kevin Wood]

Well, something's certainly not right but it would need a bit more diagnosis before the MAF sensor can be confirmed as the cause, IMHO.

Idle speed should be rock steady at around 500 RPM.

Whereabouts are you located?

A couple of things to check:

Do the throttles close completely when the accelerator is released? Is there a little slack in the cable and has the throttle stop grub screw been correctly adjusted so that the throttles close completely but don't jam in their bores?

Can you blank off the EGR valve by sandwiching a thin metal plate (e.g. bit of coke can) between it and its' base.

Any sign of air leaks into the induction system? (split ducting, plenum seals leaking, brake servo hose split, ICV bung loose in the plenum, etc.).

Kevin

[cavman]

I took the car for a spin over lunch. I disconnected the MAF sensor and apart from the engine light on the dash coming on the car performance was the same:
OK during warm up but stalling when slowing down and using the clutch.

I'm in St Albans.

[terry]

I had the same thing on my CDX on two seperate occasions, i suspected crank shaft sensor, which as it happened it was, symtems were total shut down of engine and no warning, it would restart after some time and be fine for couple of mile and then shut down again, can be dangerous if caught out in the fast lane, it may be worth checking. its located on near side side close to oil filter, easy to change, not really cheap to buy new, i bought my second one from scrapper if it turns out it is, be careful how you install replacement as cabel runs close to exaust, plugs up back of plenum pass side

 Guy from the AA couldnt even find the software for a V6 CDX on his all singing all dancing diagnostic kit so he loaded me up and took me fifty miles back home

[TheBoy]

cavman - certainly sounds like an airleak.  Due to revs, suspect somebody with a lonely braincell has adjusted the throttle body not to close fully.

[kineavy]

Cavman...I had same problem with my V6. Did the paperclip test and same fault. Took a punt and changed the MAF...it did the trick and no problems since

[cavman]

Got a new after-market MAF yesterday, fitted it (5 mins), so far the car seems fine!

Now wondering whether to re-fit the Bosch Idle Control Valve I replaced as part of my investigation with a £30 after-market one I got off e-bay, Vauxhall wanted £230 for a new one

I was surprised the MAF failed, it's got no moving parts and has clean air passing over it.


Thanks for your help guys 

[aaronjb]

I was surprised the MAF failed, it's got no moving parts and has clean air passing over it.

I'm presuming it's a hot-wire MAF on this age of Omega, in which case they do fail more often than you'd think due to the way they work - by heating the wire up to a fairly toasty temperature.  Eventually either the wire becomes brittle and snaps, or the control circuitry burns out..  For a non moving part, they have a hard life