Omega Owners Forum

Omega Help Area => Omega General Help => Topic started by: dad machine on 21 December 2011, 09:54:27

Title: hunting? when engine warm, engine repeatedly revs up and down
Post by: dad machine on 21 December 2011, 09:54:27

Hi, first post so forgive me if I'm posting this in the wrong place.
I recently bought a 1999 2.0 auto.
Car runs really well when cold but once engine warms up it seems to start over-revving. When in neutral the revs race to around 1800rpm ,then back down to about 800rpm, and then back up again. Car does this repeatedly. When in gear the engine continues to appear to rev faster than it should.
 A new idle control valve has recently been fitted and car was checked diagnostically and showed no fault codes.
I'm wondering whether this is a temperature sensor problem, or the car is possessed by a deceased chav who revs the car over and over, especially at the lights!
Any advice would be greatly appreciated

Title: Re: hunting? when engine warm, engine repeatedly revs up and down
Post by: albitz on 21 December 2011, 12:13:55

Vacuum leak ?  :-\

Title: Re: hunting? when engine warm, engine repeatedly revs up and down
Post by: dad machine on 21 December 2011, 12:30:55

Thanks for that. I'm not that much in the know to be honest.
Why would a vacuum leak only cause a problem when engine is warm and where should I look for a possible leak?
Sorry if I sound a bit thick!! Will this cause damage to the car if left alone for a few weeks?

Title: Re: hunting? when engine warm, engine repeatedly revs up and down
Post by: Sehen on 21 December 2011, 16:25:09

Most likely the coolant temp sensor. Did have the same problem with my car. It start's behaving like this when warm, or nearly warm, before it goes out of buisniss for good. Then you will have problems starting it when warm, becouse the sensor will read -35 degrees on the coolant. There was also a problem on the MFL and FL models where the plug for the sensor on the four pots that could cause this problems. There is a fiks for it, where you can by a replacement plug with a lenght of wire on it. Have to split the loom in the back and solder the new plug on with shrinking tubes on top.

Another problem that can cause this is the MAF sensor, but you have to run live data on it when it happens to find out, or borrow a known good one to see if the problems dissapear.

Title: Re: hunting? when engine warm, engine repeatedly revs up and down
Post by: Marks DTM Calib on 21 December 2011, 18:44:06

THE first thing to do with such a fault on the 2.0 is to fully clean the throttle body, idle control valve and engine breathers as per the maintenance guide.

Title: Re: hunting? when engine warm, engine repeatedly revs up and down
Post by: dad machine on 22 December 2011, 12:16:43

Thanks for that, I'll have a go over the weekend