X250 Throttle Valve - Variations on a theme!

[Beltie]

Hi Everyone,

 

I wonder if anyone, hopefully Nick! can advise me on an unusual problem I have with my 2009 3.0l X250.

 

Earlier this year, I was experiencing all the well known problems associated with the throttle body. Cutting a very long story short, the body was replaced by my local Fiat Professional dealer who are also Iveco dealers and, therefore, familiar with this engine. They had to do the job twice, as I think the first replacement was one of the original type, as it didn't require a new wiring loom. At the same time, the EGR valve was cleaned out and checked as a precaution although it was reported to be working fine.

 

The second body was fitted and all was well for about 2000 miles. I then started experiencing an odd fault, whereby when I was manouvering on site after a long run, the emissions warning light would come on, but with no other symptoms. Eventually after a few restarts, it would clear and all would be well.

 

I now have a more significant problem, which usually occurs when running at reasonable speed with a light throttle opening, i.e. with the engine not under any significant load. Suddenly the engine will start to exhibit symptoms of 'misfiring' - I know it's not likely to be a misfire but it's the best way to describe it - it starts running very badly and jerkily. Again, it can also happen during low speed manouvering. It's usually accompanied by a wheezing sound! If I floor the throttle, I can drive through it

 

There is no problem with smoke and the vehicle passed its MOT two days ago with the fault present. The garage who do my routine servicing and who I trust implicitly, hooked the 'van up to their OBD reader and found the familiar P0638 code, indicating a throttle body problem. The mechanic removed the loom and cleaned all the connections, but the fault soon re-appeared.

 

I'll take the 'van back to Fiat, but am suspicious that it may not be the throttle body itself which is faulty. Is it possible that it could be receiving erroneous signals from elsewhere, eg. Throttle Position Sensor, or even the ECU? Does anyone have any other ideas?

 

Thanks in anticipation of your response.

 

Regards

 

Roger

 

Sorry, should have added that when the 'misfire occurs, the warning light is illuminated and stays on.

[colin]

Pending an answer from Nick i'll give my standard answer, check the filter for mice, if damage is evident check the inlet pipes up to at least the air mass sensor.

[euroserv]

Hello,

 

The engine seems to be misfiring but it is just a symptom of the vehicle being in 'limp mode' while the engine management light is illuminated.

 

This sounds like classic Throttle body indeed. You should definitely check for mice as Colin suggested. They can affect the air flow meter and cause all kinds of fault codes. If all seems well with the air filter and intake pipes you should turn your attention to the EGR control solenoid valve. These don't last for ever but their life expectancy will be shortened considerably by issues with the throttle body. When the TB malfunctions, the solenoid valve has to work many times harder than usual to attempt to balance the air pressure in the induction system; leading to it getting very hot and becoming useless.

 

I am quite sure that if this item has not been replaced previously; it will need doing now. The solenoid valve is located below the windscreen scuttle in the middle of the top of the engine bay behind a bracket. It is fixed to two rubber bobbins which will often snap, so you might need a couple of these too.

 

N

 

I am assuming that the smoke emitted is black and sooty. If it is more whiteish grey then you may have injector issues.

[Beltie]

Hi Nick,

 

Thanks for coming back so quickly. There is currently no smoke at all. There was when the TB was replaced earlier in the year but now it's fine which is part of what's perplexing me.

 

Regards

 

Roger

 

I should have said that the smoke was BEFORE the T B was replaced. Since then it's been fine.