1.2 16v fault - I'm stumped!

[Martin_172]

I've got a problem with my sisters (no!) Twingo 1.2 16v currently, pretty much identical mechanically to a mk2 1.2 16v Clio.

she's owned it for years, gave very little issues, it went for an MOT last month, the test station abandoned the MOT as during emissions it started uncontrollably revving its self, they turned it off and back on and as soon as it started it continued to keep revving its self, up above 4500rpm.

It came to me, I checked it over and did notice a few things:

• It had a slight misfire at low throttle, I put plugs, coil pack, leads on it, problem solved.
• when cold started, it idles as normal at around 900rpm, if you touch the accelerator it will rev then settle at around 1500rpm for around 10 seconds, then drop back to idle, identical each time as if its programmed to do so (but I know it isn't)
• once its up to temp it just idles at 1500rpm

I stripped the throttle body off to clean it and it was very stiff and clicking when working through its motion of travel, so i replaced it with a known good one, i also replaced the throttle pedal as I know they are fairly common for issues.

With both of these replaced, the "fault" is still present.

I've ran it for a couple of weeks with no issues, so today put it into another garage for an MOT, My usual garage this time. Just had the phone call to say they have had to abandon the mot as during the emissions test its started uncontrollably revving its self.

Thoughts?!

 

[Matt Cup]

Faulty ECU?

 

[Adey.]

Smoke check for air leaks in the pvc or manifold. Can you see what the throttle is doing when its revving high? checked the throttle pedal output? is the ecu requesting it or is it a mechanical fault

 

[Mr Trailer Man]

Can only be a few things really.

It's getting more air or more fuel.

I'm thinking it's still some sort of throttle issue.

 

[Martin_172]

Smoke check for air leaks in the pvc or manifold. Can you see what the throttle is doing when its revving high? checked the throttle pedal output? is the ecu requesting it or is it a mechanical fault

Cant see the throttle body when its doing its 4500rpm revving as I cant replicate it, I've tried to dummy an emissions test on the drive but couldn't get it to do it.

the MOT tester said he thought possibly an air leak, ill attack the engine bay with a can of brake cleaner when I've collected it, I didn't think about an air leak as it was settling back to idle when cold and it would need to be a fair leak to get to 4500rpm, and only on a certain scenario!, but ill check!

the pedal data, was staying steady closed on both the old pedal and new pedal at both normal idle and the 1500rpm idle, the throttle body was fluctuating slightly a few % which looked like it was just controlling idle but I've never really looked at another car to compare, ill check that today - But now i think of it, it wasnt changing much between 900 and 1500rpm - but i assumed it probably didn't have to move much for that - but that could point towards an air leak indeed!

 

[Adey.]

I had a valver engine in a 5gtt once, ran a little lumpy with higher revs at idle, once hot it would revs its tits off, had a crack in the inlet that only showed itself when hot hot.

 

[Martin_172]

Picked it up from the garage, drove perfect the full way home, stalled it outside the house and went to re start it and it done this, turned it off, then started again to film the video, went to get the diagnostic machine, running normally no codes found.

runs perfectly on 4 cylinders when driving home, but appears to be running on 3 when it faults.