Hi all i have a 2008 Punto Active ,1.2 48kw engine,41000 miles on the clock and owned by me for the last 6 months,it has a dealer service history from new, it appears to have flat spot on the throttle,engine starts ok and idles steadily when cold at 1100 rpm and 800 when warm,the flat spot is only apparent when the smallest amount of throttle is applied and acceleration after that is ok as more acceleration is applied,but once road speed has been achieved,say 30 or 40 mph,the flat spot can then be felt as a steady speed is maintained.a kind of buffering effect,but if the throttle is released a quite violent transmission judder will be felt,as if the throttle has snapped shut but then comes back to a perfect idle.
I have had new spark plugs fitted and the HT leads checked,(replace if required all ok)and also a new air filter,the breather hoses to the air box have been removed and cleaned out.
My garage who i trust thinks it may be the throttle assy electronics not reading properly,his explanation to me was imagine a rotor with a dead segment, i can see that ok.
I found a good video from the USA of this on a US ford,they list it as replacement chip, not a complete throttle assy.
Do the techies on here think it may be a complete throttle assy as a cure?
I assume that the controlling chip for the stepper motor is not a spare part?
Or cannot be reset?
No fault codes are displayed or recorded and the tachometer stays rock steady.
Your thoughts gentleman.

Hi Don (I guess),

the reasonning seems correct in the big lines: the throttle assy is not so much complicated: one motor and two potis; all of them managed by the ECU ...
Here above you'll find some description that might help you decide where to look . It's from a 1.4 16v but I'm pretty sure it's very similar.

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)

Thank you Bernie,i am fairly sure that it will require a new throttle assy.
I spoke to my garage today but he understandably does not want commit to replacing the assembly if it should turn out not to be!and because of the potential cost ,personally if its going to cost a couple of hundred it would be worth it from a driving comfort point of view,so i might start looking and saving! then it is where to scource one from!
Thanks again.
Don.

Don1946 said:

Thank you Bernie,i am fairly sure that it will require a new throttle assy.
I spoke to my garage today but he understandably does not want commit to replacing the assembly if it should turn out not to be!and because of the potential cost ,personally if its going to cost a couple of hundred it would be worth it from a driving comfort point of view,so i might start looking and saving! then it is where to scource one from!
Thanks again.
Don.

Click to expand...

As Bernie says it's likely the throttle body. Monitoring the feedback signals with Multiecuscan or even just a multimeter my well confirm this. Sometimes cleaning the potentiometer tracks and wipers can produce a temporary fix and confirm the fault. On some you can replace just the potentiometer but I don't know about the GP.


Robert G8RPI.
Were are you located?
Robert G8RPI

g8rpi said:

As Bernie says it's likely the throttle body. Monitoring the feedback signals with Multiecuscan or even just a multimeter my well confirm this. Sometimes cleaning the potentiometer tracks and wipers can produce a temporary fix and confirm the fault. On some you can replace just the potentiometer but I don't know about the GP.


Robert G8RPI.
Were are you located?
Robert G8RPI

Click to expand...

Hello Robert,yes i think i will just have to swallow the pill!or my bank balance!
I live in Bradford and nowadays there is no Fiat dealer, i think i may have to go to the nearest one and see if they have a receptionist who i can talk tech with and not a fancy female who's boobs and bottom may look realy nice but has no car knowledge whatsoever and can only say"well if you would like to leave it with us sir"! Ahhgg!!
I thought i had located one on line which i could buy and get my guy at his garage around the corner to fit,so went to see bhim and see how he felt about it,first thing he said was where did you locate the part?in Europe said i,he named the company i was looking at and said do not touch them with a barge pole!!!!he had purchased a throttle body off of them last year for a customers Fiesta,in stock it said,but took 11 weeks to get here!
then it was in a plain white unlabelled box and was the wrong thing anyway
they didnt want to take it back and just messed him around,eventualy his bank took it up as it was on his credit card,made him an instant refund and pursued the company under EU Distance selling regs!
"Just dont go there " were his words.
SO!its back to square one,
I will visit the main dealer over the next week and see what i can find out and how much!
Thanks for your reply Robert and have a nice day!now i have depressed you!!!

If you hold throttle at approx rpm for flat spot in neutral can you hear of feel any misfiring?

I had similar issue and it was a cracked manifold due to lower rear gearbox mounting being worn and allowing excess movement. You could also hear a slight ticking on start up from very cold until the manifold heated up and mostly expanded the crack issue away.

If this is the case, you may see or smell exhaust around the manifold on first fire up when engine is cold.

My issue wasn't picked up with lambda sensor diagnostics as sensors don't behave normally until warmed up. Once warm, the manifold will have sealed enough for it to read almost normal.


Cheers

Ben

On a petrol engine the lambda (λ) sensor(s) measures the amount of oxygen in the exhaust gas compared to a reference (external air) in order for the ECU to maintain the correct air-fuel ratio at the stochïometric value. On CAT engines, there is also a λ sensor that verifies there is enough oxygen to re-oxydize the gases (after-burning).

A crack in the (exhaust) manifold will NOT change the oxygen ratio, the total gas amount only and AFAIK this quantity is not monitored by the ECU, but MAYBE for the recirculation system (EGR).

The λ sensors have a response time (typically 300 mSec) does that correspond to your flat spot ??
BTW, if it is a CAT engine, ANY leak in the pipe between both lambdas will have bad effects, similar to leals/crack in the INTAKE side of the engine...

TOTD (trick of the day ;-) :

To detect a leak or crack in the manifold / seals, gently spray some petrol where you suspect something bad: if engine iddle changes, you got an unwanted air intake there...


BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)

Thank you to both Ben and Bernie,i am 72 and the days of crawling about under cars and bonnets has gone now with the aquisition of a bad back ,hips and all the other joints around the pelvis and hips!
Tomorrow the car is going in to have a new battery fitted so will ask "my man" to have a realy good close look at the manifolds,i was thinking of having new gearbox mounts fitted anyway as the transmission snatch can be quite severe if dont handle the throttle well.
I cant seem to reproduce the flat spot while stationary,revs will rise and fall as per normal,rev counter normal,MPG is 45.4 average, it seems to need the weight of the vehicle driven to show up the hesitation,
Thanks to you both for your infomation i will get my man Steve to have a realy good look around those manifolds.
Thanks again and i will keep you both updated as to what happens.
Don.

If the throttle body is causing the problem it can easily diagnosed with a graph on MES.
It's amazing how may mechanics don't know how to use some basic diagnosis toots (basic for modern cars).

A hesitation can be caused by numerous issues: fuel flow/fuel pressure, clogged filters, air leak, spark plugs, spark gap, HT leads, coils, injectors, accelerator pedal, temp sensors, lambda/O2 sensor, .. etc.. etc

In short your car needs a proper diagnoses.. not just throwing parts at it, in hope it will cure the problem.