Audi A4 2.0 TDI Rough idle

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fenwick458
Newbie
Posts: 4
Joined: Wed Nov 21, 2018 9:40 pm

Re: Audi A4 2.0 TDI Rough idle

Post by fenwick458 » Fri Jun 21, 2019 9:24 pm

nelnun wrote:
Sun Feb 11, 2018 10:45 pm

I've removed the DRV today and cleaned it, no joy! I've mande a "trim reset" (coding II = 10008 ), let see tomorrow, but I don't think it will work!
when I try to do this, the "Coding II" button is greyed out, so I can't.
anyone know how i can do it?

Iver
TwoWaves
TwoWaves
Posts: 90
Joined: Mon May 27, 2019 2:55 pm

Re: Audi A4 2.0 TDI Rough idle

Post by Iver » Mon Jun 24, 2019 1:37 pm

Hi Fenwick

This is a long thread now and is dealing with many different cars. They may have the same fault but we have no guarantees there.

Let us try and stick to your Van alone
when Idling the specified was about 30 and actual was jumping around all over the place, and when driving the numbers were way higher and they were very closely matched, so it seems to be only at idle or below 1500 rpm ish that there is a problem.
At idle if you have FRP jumping around then looking back through this thread you will see that it is often the Rail Pressure Regulator (FPR) on the Rail that fails not the DRV / IMV on the pump. Often perhaps not always.

As long as your low pressure to the pump, through the filter is all good then ultimately the DRV & the FPR will be control fuel pressure. It is not just a case of one is for fine tuning. Dependant on Engine Temprature among other factors they work one at a time or together. There is a clear documented strategy that is employed.

Regulation by the fuel pressure regulating valve N276 - On the Rail
When the engine is started, the high fuel pressure is regulated by the fuel pressure regulating valve N276
to warm up the fuel. To warm up the fuel quickly, more fuel is transported by the high-pressure pump and is
compressed as required. The excess fuel is sent back to the fuel return by the fuel pressure regulating valve

Regulation by the fuel metering valve N290 - On the Pump
The high fuel pressure is regulated by the fuel metering valve N290 when there are high injection Quantities and high rail pressures. This results in on demand regulation of the high fuel pressure. The power consumption of the high-pressure pump is reduced and unnecessary fuel heating is avoided.

Regulation by both valves
At idle, when decelerating and with small injection quantities, the fuel pressure is regulated by both valves at the same time. This allows precise regulation that improves the idling quality and the change-over to deceleration.


Now we know that at Idle both valves are used then we now have to prove which one is faulty.

We also now that the N290 is used for High Demand, so that points to the FRP N276 possibly being the culprit however we still need evidence to be sure we are not making mistakes.

Post 8 on Page 1 of this thread shows a good procedure to isolate one and then the other using an inexpensive tool bought online to diagnose this efficiently & correctly

I have fixed dozens of these with these symptoms and it has always been N276 at fault. Unfortunately VW sell the complete rail at about £700, that may have changed now so check for yourself. Even so with the power of the web im sure you can find an alternative if you choose not to go genuine. Not advisable but .....

garethkerr
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Joined: Mon Nov 11, 2019 1:19 pm

Re: Audi A4 2.0 TDI Rough idle

Post by garethkerr » Mon Nov 11, 2019 1:25 pm

Diesel Johnny,

I have a T5 with a 2.0 TDI engine with the rough idling, after resetting IMV valve was good for around a month then back to the rough idle and as if the fuel line is being crimped at times when driving especially when cold.

What was your fix in the end? Many thanks in advance. I was possibly going to try a new IMV Vavle?

fenwick458
Newbie
Posts: 4
Joined: Wed Nov 21, 2018 9:40 pm

Re: Audi A4 2.0 TDI Rough idle

Post by fenwick458 » Sun Nov 24, 2019 6:51 am

Iver<
Thanks for the reply. When I changed the DRV last year it seemd to fix the problem, it idles and drives fine, been ok for over a year but the only slight issue is it goes into limp ode if you rev it over 3000rpm.
garethkerr wrote:
Mon Nov 11, 2019 1:25 pm
after resetting IMV valve was good for around a month then back to the rough idle and as if the fuel line is being crimped at times when driving especially when cold.

What was your fix in the end? Many thanks in advance. I was possibly going to try a new IMV Vavle?
How do you reset the IMV?

dieseljohnny
OneWave
OneWave
Posts: 28
Joined: Mon Oct 12, 2015 9:08 pm

Re: Audi A4 2.0 TDI Rough idle

Post by dieseljohnny » Tue Nov 26, 2019 8:51 pm

In the A4 I dealt with it was the pressure regulator on the rail

garethkerr wrote:
Mon Nov 11, 2019 1:25 pm
Diesel Johnny,

I have a T5 with a 2.0 TDI engine with the rough idling, after resetting IMV valve was good for around a month then back to the rough idle and as if the fuel line is being crimped at times when driving especially when cold.

What was your fix in the end? Many thanks in advance. I was possibly going to try a new IMV Vavle?

Iver
TwoWaves
TwoWaves
Posts: 90
Joined: Mon May 27, 2019 2:55 pm

Re: Audi A4 2.0 TDI Rough idle

Post by Iver » Wed Nov 27, 2019 8:35 pm

In my experience, and I have solved dozens, it is always the Pressure regulator on the Rail.

That does not mean that you should not Test, Measure, and Prove your particular vehicle.


ELSA or ERWIN will clarify which does what and when Make good use of it.

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