2004 K12 1.216v SX not revving properly at high end

[ardvaaark]

Hi

I have 2004 1.2 16v SX.

It starts and idles very well.

It will rev full range under no load.

In 2nd gear or especially 3rd 4th or 5th it will not rev past about 4.5k to 5k revs.

It is like it is misfiring - almost like it's on the limiter. But of course it is not.

Now it has started sometimes misfiring at low revs - intermittently. I think the two are linked.

It has had new plugs and new air filter.

I have cleaned a out the throttle body there was a fair bit of muck. - this seems to have helped the low rev missing but not the top end that is still poor.

I have tried to recalibrate the throttle using a youtube video - not sure how successful this has been.

OBD says no codes listed.

It is like it is not getting the correct fuel air mixture at high revs.

The only things I can think of now are:

Air leak on the intake somewhere - maybe one of those orings or seals?

OR

The air flow sensor.

Any ideas?

Thanks for looking.

 

[Micra Paul]

A quick cheap suitable test now would be to unplug the mass airflow sensor at the throttle body & test drive to check if the rev limiting shuddering misfire is reduced?

It will flag a fault code engine check light that will shortly reset itself when the mass air sensor is reconnected after a few stop start on off cycles.

 

[ardvaaark]

Thanks for suggestion @Micra Paul I will absolutely do that

 

[ardvaaark]

OK I have got some codes on the OBD now.

it has got...

P0304 Cylinder 4 misfire
P0113 Intake Air Temp Sensor 1 Circuit high
P0107 MAP Barometric Pressure Circuit Low

I have cleared them all and run it... The problem at 4.5k revs still comes but the codes have not come back...

I suppose the 2 most serious are the misfire and the MAP sensor....

I will try a new coil on 4 and a new MAP sensor I think.

 

[Micra Paul]

Quicker & cheaper to simply interchange the apparently misfiring no 4 coil for one of either cyls no 1, 2, or 3 coils to test if the apparent misfire fault code shifts?

Our juddering, shuddering & kangarooing Micra was tamed with the TB mass air flow sensor unplugged & it drove ok with the corresponding CEL & even passed an MOT!

As the banger was 20 years old we were reluctant to spend £90 on a replacement OE spec mass air flow sensor some 3 years ago but with the MOT straight through pass & no additional fault codes I bit the expense bullet & fitted one.

Now 2 years on & another recent straight through MOT pass the 23 year old banger is on 85K & running just as good as it was designed & built for.

Happy days.