Disabling the diesel throttle valve (TVA Off)

TVA Off disables the diesel throttle valve (TVA, throttle valve actuator) in the ECU software. The ECU stops controlling and monitoring the valve, and actuator and position sensor faults, along with the limp mode they trigger, go away. For tuners: send us the original file and get a ready-to-flash file with corrected checksums, on average in 30–60 minutes.

Why a diesel has a throttle valve

On a petrol engine the throttle meters the air and with it the power. A diesel's power is set by the amount of fuel injected, so most of the time the throttle sits wide open. According to Pierburg, a diesel throttle stays open when unpowered as well. It is mounted at the entry to the intake manifold, where exhaust gas from the EGR system joins the fresh air.

A diesel needs a lot of recirculated exhaust gas, and Pierburg quotes EGR rates of up to 60 %. That is why the valve is closed now and then:

Do not confuse the throttle with swirl flaps: those sit in each cylinder's intake ports and are disabled by a different service, Flaps Off. VW adds to the confusion by calling the diesel throttle the "intake manifold flap", so in VAG documentation and scan tools its faults read like manifold flap faults.

Why the throttle fails

The valve lives in a dirty flow: oil mist from the crankcase ventilation passes through it, and EGR soot enters right behind it. Over time the housing and spindle build up deposits and the actuator starts working against resistance. Pierburg, which makes these units, warns that cleaning will not save a faulty throttle and can damage a working one.

Two known cases from Pierburg's service information:

• VW Golf V, Touran and Audi A3 with the 2.0 TDI. The display shows "Emission, Workshop", the warning light stays on and the engine shudders after switch-off. Engine temperature can also climb, because the throttle and the cooling fan share one fuse.
• Fiat Ducato 3.0 JTD, Iveco Daily IV, Peugeot Boxer III and Citroën Jumper 3.0 HDi. Moisture gets in through the cable connector and the actuator corrodes inside. The result is limp mode and code P0638.

Symptoms and fault codes

A Check Engine light, limp mode with reduced power and shaking at switch-off. If the valve is stuck partly closed, the engine runs short of air. SAE has a dedicated code family for the diesel throttle, diesel intake air flow control. Some ECUs log electronic throttle codes instead, the same as on petrol cars: P0638, P2102.

What changes in the software

TVA Off rewrites the ECU logic so it no longer commands or monitors the valve. Without control the valve stays open.

To be straight about the side effects: the engine may give a slight shudder at switch-off, since nothing cuts its air any more. If the EGR stays active, in some operating points it will not pull as much gas as the ECU expects. On a car that still has its DPF, regenerations may work less well without the throttle. When EGR Off and DPF Off go into the same file, those last two jobs of the throttle disappear anyway. Checksums are recalculated, so the file is ready to flash straight away.

What to do with the valve

• Opens freely all the way: leave it in place. The actuator connector can be unplugged after TVA Off.
• Stuck partly closed: remove the housing and make sure the passage is fully open. Otherwise the engine will run short of air under load.
• Housing removed altogether: check that the hose or spacer in its place is tight, because a boost leak will set its own faults.

How to order the file

1. Read the original file via OBD or on the bench (bench, boot) with the tool you use. We need an unmodified stock file.
2. Upload it to the portal and select TVA OFF. Tell us what stays on the car: EGR, DPF, the throttle itself.
3. Get the finished file with recalculated checksums, on average within 30–60 minutes.
4. Flash the file, clear the faults and check that no new throttle faults appear.

The diesel throttle takes part in EGR control and DPF regeneration, which means it helps reduce emissions. In a number of countries, changing emissions-related components on vehicles used on public roads is prohibited and may cause an inspection failure. Responsibility for using the file lies with the vehicle owner.