New Throttle Body

[gjasmith]

Hello,
Car is a 2012 220CDi coupe, OM651 engine.

It was going into limp mode with P0122 and live data showed throttle stuck at 99.4%

There was no movement from the throttle flap at any time, wiring plug (when unplugged) was giving 5v on pins 1 & 4, Pin 5 at 0v.

So I put a new Bosch throttle body in, turned ignition to pos 2 and throttle flap goes back and forth a few times (live data reflects this) and returns by spring to its fully open position. Live data shows this as being 88.64%.

Starts up OK but throws up error P2112 which appears to be saying that the actuator is stuck when clearly the car knows it moves on startup.

Does it need the ECU updated with the standard resistance values from the new throttle? and if so is this a Star only thing or is there a DIY level scan tool which can do this?

Thanks for reading.
Gordon.

 

[ALFAitalia]

Its not a throttle body....you have a diesel so it doesn't have a throttle as such.......engine speed is controlled purely by injector pressure and duration. That's a shutter valve....its there to shut when you switch off to minimise air flow into the engine so you don't get that THUMP when you switch off the engine like in in old school dervs....it also moves slightly to aid EGR function and reduces the likely hood of "engine runaway". It should be wide open when engine is running in 95% of circumstances. It wont affect running unless its shutting when it shouldn't though.....some diesel tuners remove them all together for better air flow.

 

[zipdip]

Welcome aboard ,what Alfa said is right.

 

[Supernoodle]

It is a throttle valve on a Diesel.

You don't put resistance values in the PCM but there is a new throttle valve routine. That will clear the end stop adaption values that are stored and relearn for the new valve.

Not sure which non Star tools support this.

 

[ALFAitalia]

Its NOT a throttle!....what use would it be on a diesel!!!???? Direct injection dervs are effectively always at full throttle as fgar as air flow goes.....only the amount of fuel injected (via pressure and duration) affect engine and ultimately road speed. If you removed it completely it would run 95% just the same.

Outline and Operation of Intake Shutter | Your Online Mechanic

Explained: Why Diesel engines need a throttle body & throttle plate

Explained: Why Diesel engines need a throttle body & throttle plate

www.team-bhp.com

 

[gjasmith]

Hello all,
Thanks for replies and aplogies if my terminology is a bit off, I was calling it a throttle body because that was the fault code description and the name of the part as listed on Ebay.

Thanks for the links Alfa, in the second one it mentions the angle of the (and they call it the throttle plate) being off the perpendicular, strangely the old one was like this but the new one looks to be near enough 90°, also as you said, and going by the live data it is nearly always fully open but closes briefly when the ignition is turned off.

I just can't figure out why the car complains it is stuck shut while the live data shows it to be working as it should.

I think I may have to find an upgrade to my ancient ELM/Win XP combo

Gordon.

 

[Supernoodle]

Its NOT a throttle!....what use would it be on a diesel!!!???? Direct injection dervs are effectively always at full throttle as fgar as air flow goes.....only the amount of fuel injected (via pressure and duration) affect engine and ultimately road speed. If you removed it completely it would run 95% just the same.

Outline and Operation of Intake Shutter | Your Online Mechanic

Explained: Why Diesel engines need a throttle body & throttle plate

Explained: Why Diesel engines need a throttle body & throttle plate

www.team-bhp.com

It's not a throttle... So the very article you linked to is entitled "why diesel engines need a throttle body and plate" .....


If you want use the ISO diagnostic terminology it's a diesel intake airflow control valve.....something that controls air flow is a throttle!

Yes it may be normally open on a Diesel but as you've rightly stated it can be partially closed to create a sight depression in the intake, increasing the pressure differential across the EGR, increasing flow. When it does this it only partially closes, ie it throttles the air.

 

[ALFAitalia]

Hmm....but throttles, in the conventional use of the word in the automotive world, control engine speed whereas shutter valves (or anti shudder valves) don't. And the answer "why diesels need them" in that link was that they didn't. And as said some diesel tuners remove them completely.

 

[Supernoodle]

Even with an old carb engine, an intake depression is caused by the throttling of the air as it passes a venturi, sucking fuel into the engine. So yes, throttle position is analogous to fuel flow and power.

On electronic fuel injection engines the throttle controls air in, injectors the fuel flow. Exactly the same on a Diesel. Yes on a Diesel the throttle is kept open to maximise volumetric effeciency as they don't need a fixed air fuel ratio, you just vary fuel into the engine. If you're only concern is power, do away with the throttle by all means.

Unfortunately emission legislation means you have to think about reducing NOx. That means using EGR. At low loads the exhaust back pressure isn't too different to intake pressure. So you can open the EGR valve but with little pressure differential you have little flow. So you either need to increase the exhaust back pressure or reduce the intake pressure. By throttling (note, not shutting off) the air flow into engine you get a pressure differential between intake and exhaust and hence EGR flow.

So just like a petrol, the throttle is restricting air flow into the engine, but the reason for doing so is very different.

 

[Supernoodle]

Hello all,
Thanks for replies and aplogies if my terminology is a bit off, I was calling it a throttle body because that was the fault code description and the name of the part as listed on Ebay.

Thanks for the links Alfa, in the second one it mentions the angle of the (and they call it the throttle plate) being off the perpendicular, strangely the old one was like this but the new one looks to be near enough 90°, also as you said, and going by the live data it is nearly always fully open but closes briefly when the ignition is turned off.

I just can't figure out why the car complains it is stuck shut while the live data shows it to be working as it should.

I think I may have to find an upgrade to my ancient ELM/Win XP combo

Gordon.

The PCM will complain of a valve stuck if it can't drive the valve close to 100% or at least some tolerance within the learnt end stop.
It will have learnt the end stop values of your old part. Assume when it was at the end stop that was at 95%, you just throw on your new part and it only gets to 88%, PCM assumes it's not at the stop yet, it will keep driving the valve, but it's position isn't changing...a stuck valve.