Technical Engine tick-over not steady after fitting Marelli Throttle Body - X250, 2.3, 130 Multijet, 2009.

[Davidod]

Just had a Marelli Throttle Body fitted after intermittent P0638/9 errors.

Since then, the engine tick-over has been a bit jittery, that is to say, not the absolute steady RPM that it used to be. Can anyone let me know if there is any software upgrades that might be needed after fitting the Marelli TB?

 

[bugsymike]

Just had a Marelli Throttle Body fitted after intermittent P0638/9 errors.

Since then, the engine tick-over has been a bit jittery, that is to say, not the absolute steady RPM that it used to be. Can anyone let me know if there is any software upgrades that might be needed after fitting the Marelli TB?

I may be wrong , but isn't there a program in MES or similar to match the replacement throttle body to the vehicle.?
Perhaps others on Forum can advise.

 

[Davidod]

I may be wrong , but isn't there a program in MES or similar to match the replacement throttle body to the vehicle.?
Perhaps others on Forum can advise.

Thank you for that suggestion.

I'd just like to add, that this is especially noticeable when you drive forward in traffic with the engine just at tick-over speed. It makes it quite jerky. However, driving at regular road speeds it is not really noticeable. I have not had any errors since changing the throttle body. The mechanic did say that it may be necessary to also fit a new EGR Valve.

 

[bugsymike]

Thank you for that suggestion.

I'd just like to add, that this is especially noticeable when you drive forward in traffic with the engine just at tick-over speed. It makes it quite jerky. However, driving at regular road speeds it is not really noticeable. I have not had any errors since changing the throttle body. The mechanic did say that it may be necessary to also fit a new EGR Valve.

Any error codes read or mentioned by mechanic etc.?

 

[Davidod]

Any error codes read or mentioned by mechanic etc.?

No warning lights on, but I haven't been back to the mechanic. He asked me to drive it for a couple of weeks to see what transpires. I suppose I'd better do that. Haven't had the bill yet either, not looking forward to it.

 

[bugsymike]

No warning lights on, but I haven't been back to the mechanic. He asked me to drive it for a couple of weeks to see what transpires. I suppose I'd better do that. Haven't had the bill yet either, not looking forward to it.

Your mechanic sounds like I used to be before retiring, charge on results , rather than like the big garages, bill every minute regardless of whether their staff have fixed what you came in for or not!
Better to have a happy customer and repeat business, than an unhappy customer who never comes back and tells all their friends!

 

[Anthony489]

Hi

I think it's unlikely that the throttle body would have any effect on idling, unlike a petrol engine the throttle body on a diesel is part of the emissions control process and is not used to control power/rpm. That is done by control of the fuel quantity injected.

If your EGR valve is stuck open that could possibly upset idle speed.

One thing that can upset idle RPM is a fault in the battery or charging setup, and the ECU raises idle speed to get charge back in the battery. However, that still gives a steady (albeit raised) idle and will have a battery warning lamp. Your symptoms don't match this.

 

[Davidod]

If your EGR valve is stuck open that could possibly upset idle speed.

I have also been aware of a more abrupt change in the engine response when I press or release the accelerator pedal. The silky raise or fall in RPM has gone. Could that also point to the EGR Valve?

 

[Davidod]

Could I take up from my last post regarding the idle speed of the engine. I have attached a recording of this in the hope that hearing the engine might help in forming an opinion on the cause.

To recap: I had a Marelli Throttle Body fitted after intermittent P0638/9 errors. The EGR Valve was not charged as the mechanic did not feel that it would sort out the issue, however he did feel that re-setting up the ECU might sort the problem. For that, he says I would have to go to a Fiat garage.

I have driven over 4000 kilometers since having the throttle body replaced, and when driving there is no noticeable effect, the engine performs as normal. The fuel consumption is normal. No warning lights have come on. It is only the tick-over that shows this non-constant RPM.

Any opinions would be very welcome. Thank you.

 

[bugsymike]

Sounds very much like the old diesel lorries and buses of yesterday "hunting" at idle.
I wonder if calibration of the new throttle body may be the answer, I will say I have no personal experience of doing that, but maybe someone in the MES section would have more knowledge regarding that.
I am assuming nothing else when driving makes this happen, purely when idling?

 

[jackwhoo]

Hi,
You really need to go back to the mechanic who did the work.

Please let us know the outcome.

Best wishes
Jack

 

[jackwhoo]

If you are able look to see if the butterfly is closing and opening as faulty one in video.

 

[theoneandonly]

I may be wrong , but isn't there a program in MES or similar to match the replacement throttle body to the vehicle.?
Perhaps others on Forum can advise.

I cant see any way to code or learn the throttle body to the ECU within MES
on the early model Bosch ECUthere is a test procedure. not on later model

 

[bugsymike]

It may depend on makes etc. There is a few bits online, don't know if relevant.
"Do you have to reset a throttle body after replacing it?
In many cases, it's recommended to reset the car's computer after replacing the throttle position sensor. This can help the car's computer relearn the new sensor's parameters and ensure that it operates optimally"
"Can you recalibrate a throttle body?
Throttle Body Idle Air Calibration After Installation
Most manufacturers require an OBD-II bidirectional scan tool to perform the calibration. Some manufacturers have published manual calibration and relearning methods. However, it is recommended to perform this step with a scan tool that will support ETB relearning."

 

[Davidod]

If you are able look to see if the butterfly is closing and opening as faulty one in video.

I'll check that. Thanks 'jackwhoo'.

I cant see any way to code or learn the throttle body to the ECU within MES
on the early model Bosch ECUthere is a test procedure. not on later model

Very much appreciate that research. I'll be showing that to the mechanic. Thanks 'theoneandonly'.

It may depend on makes etc. There is a few bits online, don't know if relevant.
"Do you have to reset a throttle body after replacing it?
In many cases, it's recommended to reset the car's computer after replacing the throttle position sensor. This can help the car's computer relearn the new sensor's parameters and ensure that it operates optimally"
"Can you recalibrate a throttle body?
Throttle Body Idle Air Calibration After Installation
Most manufacturers require an OBD-II bidirectional scan tool to perform the calibration. Some manufacturers have published manual calibration and relearning methods. However, it is recommended to perform this step with a scan tool that will support ETB relearning."

Appreciate your comments. I have been looking to find a mechanic with the right gear, manuals and expertise. Good to know the detail. Many thanks 'bugsymike'.

 

[Anthony489]

Hi

I can't be 100% certain, but I think calibrating a throttle body is only critical for a petrol engine where the TB determines the idle airflow and hence idle RPM. At idle the TB will be almost completely closed as the airflow is so small.

With a diesel, the airflow at idle is larger as the idle speed is controlled by the amount of fuel injected. The air to fuel ratio is a lot higher than with a petrol, as diesels are happy to operate in a "lean burn/excess air" condition whereas petrols will misfire or not run at all if too lean.

The diesel TB is used to control manifold pressure under cruise conditions to aid the EGR process (old school diesels had no TBs.) It should not affect idle speed unless it incorrectly closes completely, and chokes off nearly all the airflow (something it should only do when you switch off). You might be able to take off the large air feed hose and observe what the TB flap is doing, use a small mirror if necessary. To prove a point, I guess you could temporarily hold a pencil or similar in there to prevent it closing completely.

 

[bugsymike]

Hi

I can't be 100% certain, but I think calibrating a throttle body is only critical for a petrol engine where the TB determines the idle airflow and hence idle RPM. At idle the TB will be almost completely closed as the airflow is so small.

With a diesel, the airflow at idle is larger as the idle speed is controlled by the amount of fuel injected. The air to fuel ratio is a lot higher than with a petrol, as diesels are happy to operate in a "lean burn/excess air" condition whereas petrols will misfire or not run at all if too lean.

The diesel TB is used to control manifold pressure under cruise conditions to aid the EGR process (old school diesels had no TBs.) It should not affect idle speed unless it incorrectly closes completely, and chokes off nearly all the airflow (something it should only do when you switch off). You might be able to take off the large air feed hose and observe what the TB flap is doing, use a small mirror if necessary. To prove a point, I guess you could temporarily hold a pencil or similar in there to prevent it closing completely.

Some good points to try @Anthony489 suggests.
I agree re the general principles re petrol/diesel throttle body especially on older designs, possible with all the sensors they incorporate these days, including the anti runaway protection of closing the throttle totally when ignition off the need for more precise adjustment may affect it.
Do you think a poor accelerator pedal potentiometer could give a "dead spot" at idle, although it should show up on diagnostics I would have thought, mind you thinking about it when released it should read at idle it should not affect it.

 

[Davidod]

You might be able to take off the large air feed hose and observe what the TB flap is doing, use a small mirror if necessary. To prove a point, I guess you could temporarily hold a pencil or similar in there to prevent it closing completely.

Thank you for that suggestion. The mechanic does not believe that the EGR is sticky, but I'm heading back to him and I'll ask him to try your suggestion.

Do you think a poor accelerator pedal potentiometer could give a "dead spot" at idle, although it should show up on diagnostics I would have thought, mind you thinking about it when released it should read at idle it should not affect it.

Thanks for the additional post: Before replacing the TB, the accelerator response was silky smooth and perfectly steady tick-over. It was an immediate change after fitting the new TB. There are no issues showing on the mechanics OBD unit.

 

[bugsymike]

Thanks for the additional post: Before replacing the TB, the accelerator response was silky smooth and perfectly steady tick-over. It was an immediate change after fitting the new TB. There are no issues showing on the mechanics OBD unit.

So it is pointing to the throttle body, hopefully your mechanic can find the solution.

 

[Davidod]

So it is pointing to the throttle body, hopefully your mechanic can find the solution.

Not impossible, but hopefully not