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        General >> Problems >> Problems with engine revs changing up and down
        
(Message started by: mondeoman on Apr 7^th, 2015, 9:33am)

Title: Problems with engine revs changing up and down
Post by mondeoman on Apr 7^th, 2015, 9:33am

Hi,

I have a 2.9 24v Ford Scorpio and it has just started to develop a fault. Sometimes the tick over speed is quite fast and if I rev the engine then on occasions that increased it further. Driving for a period of time yesterday on cruise control the revs started to drop for a second, then pick up for a second and then drop again. It might do that for several cycles before stopping for a bit before starting it all over again. Any ideas what could be causing it?

I am also fed up of getting warped front discs and have gone through several in a short period of time. I am not being hard on the brakes and my wife's late 2.3 Scorpio from same disc manufacturer have not had any problems. I can understand once, but several times on a short period of time?

Title: Re: Problems with engine revs changing up and down
Post by Simmo on Apr 8^th, 2015, 7:42am

The first thing to do is clean the MAF (http://www.fordscorpio.co.uk/cleanmaf.htm). You may also want to look at the link in the article about testing it if you have the facilities. :)

Title: Re: Problems with engine revs changing up and down
Post by mondeoman on Apr 8^th, 2015, 2:35pm

Thanks, I'll have a look at the MAF tonight and try and clean it.

I've had the car serviced today and the mechanic thinks its the Idle Air Control Valve as when he compresses the air flow pipe the car idle drops. He claims he has just replaced these in the past on other cars and it has solved the problem. The information on this website suggests it's not normally the cause of an idle problem?

Cheers,

Simon

Title: Re: Problems with engine revs changing up and down
Post by mondeoman on Apr 8^th, 2015, 7:23pm

I have checked the maf sensor and I cleaned it and it has not solved the problem. Any suggestions on what else to try?

Cheers,

Simon

Title: Re: Problems with engine revs changing up and down
Post by Glyn on Apr 8^th, 2015, 8:31pm

I have had the same problem in the past and changing the idle air control valve made no difference. After a long investigation it turned out to be a crack in a plastic T piece in the vacuum lines behind the engine in the gap before the bulkhead, which could not be seen. the mechanic found it by spraying carb cleaner behind the engine(with it idling) and noted the change in the idle engine note.
Good luck
Glyn

Title: Re: Problems with engine revs changing up and down
Post by mondeoman on Apr 16^th, 2015, 11:33am

A friend of mine disconnected the plug from the idle control valve and the engine stopped which he claims told him it was an electrical fault, rather than an air leak. Does this sound right and if so any pointers of what to look at as probably cause?

Cheers,

Simon

Title: Re: Problems with engine revs changing up and down
Post by mondeoman on Jun 11^th, 2015, 10:43am

I have finally managed to get the ECU read and there are no fault codes. People are telling me that points to an air leak causing the fast tick over. Does that sound correct? I have been told to seek a garage with a smoke generator to look for leaks.

Does this rule out any chance of an electrical fault?

Cheers,

Simon

Title: Re: Problems with engine revs changing up and down
Post by mondeoman on Jun 17^th, 2015, 1:16pm

A garage has identified the cause of the fast idle problem and apparently it is a control unit failure. The wiring is fine and they have managed to control the idle by disconnecting the idle control valve which the garage claims should be ok, except in a cold winter where i may need to apply a little throttle when stationary.
They have indicated that the control unit is linked to the immobilizer system and a replacement part will be difficult to source, or repair. If I managed to get a replacement unit on here then someone would need to program it for the immobilizer. Does all of this sound correct?

The Cosworth unit is quite rare?

Cheers,

Simon

Title: Re: Problems with engine revs changing up and down
Post by amigafan2003 on Jun 17^th, 2015, 11:04pm

on 06/17/15 at 13:16:16, mondeoman wrote:

Does all of this sound correct?

No.

As already suggested, check the t-piece joining the vacuum lines located under the rear of the inlet manifold.

If you need a new ecru it needs to be done by someone with a wds machine, but I don't think your ecu is faulty.

FYI - even with the idle valve disconnected it'll be fine in winter with bit of throttleto keep the revs up and left foot braking until the engine gets hot.

Title: Re: Problems with engine revs changing up and down
Post by mondeoman on Jun 18^th, 2015, 11:30am

I know the garage have done a smoke test on the car and found some minor leaks which have been resolved. Will this test have picked up a fault with the vacuum lines?

Cheers,

Simon

Title: Re: Problems with engine revs changing up and down
Post by Glyn on Jun 18^th, 2015, 11:44am

I doubt it. It's easier to spot the smoke blowing away than see it being sucked in with the engine running.
Try spraying carb cleaner round the back of the manifold in particular with the engine idling and listen for a change in the tick-over.

Title: Re: Problems with engine revs changing up and down
Post by Tenfut on Jun 18^th, 2015, 12:59pm

I had this problem a few years ago. Turned out that one leg of the plastic T piece had broken off. I got one made up out of brass and problem solved. Fairly difficult to locate and a few scarred knuckles when replacing.
Tony

Title: Re: Problems with engine revs changing up and down
Post by Glyn on Jun 18^th, 2015, 7:34pm

Tenfut posted -

I had this problem a few years ago. Turned out that one leg of the plastic T piece had broken off

I had same problem (see my previous post) and managed to get a plastic T piece that fitted from a fuel line.

Title: Re: Problems with engine revs changing up and down
Post by amigafan2003 on Jun 19^th, 2015, 12:02am

on 06/18/15 at 19:34:10, Glyn wrote:

Yes - I had the same on the S reg I used to have - replaced it with a T had spare in my aquarium box. When I got the Y reg, I replced the T as preventative maintainence and it broke in my hand as I was removing it.

Title: Re: Problems with engine revs changing up and down
Post by Glyn on Jun 19^th, 2015, 1:14am

Good move. Both mine replaced too.