Technical Erratic high revs preventing MOT test

[Woodchip]

My 2001 1.2 8v Punto is revving so erratically that the MOT tester can't do the emissions test. I've tried cleaning the throttle body & resetting the Self Adaption & the Phonic Wheel using Multiecuscan which seemed the likely solutions but no joy.

Idle is reasonably steady, about 730 to 762 when the target is 750rpm but taking it up to 2000rpm or higher it just goes up & down with no way to keep pace with it using either the throttle pedal or hand control under the bonnet. The MOT emissions test requires a steady high rev (3500 I think?) for a short time which is just not possible at the moment.

Am I missing something obvious? There are no fault codes present. All suggestions appreciated ...

Help

 

[blu73]

sound like a vacuum leak, check the vacuum hoses for splits and/or cracks and not loose at ends etc. And that the throttle body isn't loose. You can quite often hear the leak if you stand with the bonnet open and engine running - not always though.

Just so everyone knows, what engine we talking about here?

 

[fingers99]

Vacuum leak or faulty throttle body I'd think. If deisel, no real idea.

 

[Woodchip]

Engine is the SOHC 1.2 8 valve petrol. I don't really see a vacuum system on this car - only visible hose is the crankcase ventilation from rocker cover to the air inlet - with a thinner fork into the inlet manifold which I have to assume is the vacuum line?

I've rechecked the throttle body fit - I had removed it to clean it - and that has no leaks.

I've booked it in to a Fiat dealer this afternoon which gives me only 3 hours to solve it myself - it doesn't look good

 

[blu73]

There is a few on the back of the throttle body too. There is a nice diagram in the cinq/sei guides that i believe fingers posted.

 

[Woodchip]

Thanks, Blu73. Seems too different to what I have - here are some pics to illustrate:

View from left:

View from right:

from the front:


I can't see any other hoses connecting - I looked underneath the plastic manifold with a mirror & couldn't see anything there

 

[fingers99]

You have an MPI (Mk2) Punto, from what I can see. Servo hose, breather hose (they do crack where the small bore pipe joins the larger hose) or IAC, methinks.

 

[Woodchip]

My mistake; it is indeed a Mk2 - not much hope for me if I don't even know that

I've run out of time so it's off to the dealer now.

 

[Woodchip]

OK, back from the Fiat dealer & they have suggested it could be the head gasket! But I got the impression that was just a best guess.

So I'm £60 lighter & not really any further forward than I was using my own knowledge & Multiecuscan (plus a bit of input from this forum )

I'll keep plodding away at this & post if I make a breakthrough

 

[Woodchip]

Problem Solved!!!

And entirely due to this forum :worship:

Here's the thread that made it all possible: https://www.fiatforum.com/punto-ii/22329-erratic-revs-mot.html

Thanks to Kebab, NumanR, The Sultan et al.

Front wheels raised by the (slightly sceptical but willing to try) MOT tester & the rpm was stable. Emissions passed

BTW, I contacted VOSA who advised that the computer systems at testing stations are provided with test procedures for all cars by them. The MOT tester was quite correctly following those steps as he has done with hundreds of Puntos before (including mine) without encountering this problem. I remain puzzled about why mine has played up this time

Puzzled but relieved - good for another year

 

[blu73]

thats quite random that is but glad you got your 12 month ticket