Engine Won't Rev Up: Troubleshooting & Fixes

Hello,

I've noticed that my 1.9 TDI 81 kW, manufactured in 1997, doesn't rev up as quickly in first and second gear. The engine initially revs slowly to about 2200 rpm, then there's a strong jolt of acceleration, and the RPM increases rapidly. When accelerating in higher gears, I don't notice anything unusual; the engine pulls well.
Since I usually drive focusing on torque, I didn't notice the effect for a long time, but I believe that this effect was not present before the timing belt change at 90,000 km.
I believe that if you drive a few meters and the engine speed slightly increases, then fully pressing the accelerator pedal results in good and consistent acceleration.
My Audi service center doesn't know what to do either.

To add to this, the car has an optional chip tuning module (140 hp and 320 Nm), which I mainly use for overtaking maneuvers. But it's most noticeable here: previously, when accelerating strongly in first and second gear, the wheels would spin. Now, even at speeds up to around 2200 rpm, there's significant wheelspin, and then suddenly, full power kicks in.

What could the problem be?

Hi,

What does the error memory contain?

Best regards, Rainer.

Hello,
Does the engine have a variable geometry turbocharger (VGT) and an air-to-liquid intercooler (ATL)?
If that's the case, the adjustment mechanism might get stuck, causing the turbocharger to spool up slowly and hesitantly.
Best regards,
Günther.

Hi,

Quote:

1.9 TDI engine, 81 kW, manufactured in 1997.

I don't know of any 1.9-liter engines with 81 kW that don't have a VTG (Variable Turbine Geometry), so it is definitely possible. Therefore, read technical articles about VTGs and perform the described test for mobility using a vacuum pump or large syringe.

Best regards,

January.

Hello,
It also suggests that he may have been driving in a way that prioritized torque for a long time. The TDI should occasionally be allowed to 'rev up' after it has warmed up, so that the catalytic converter and other components can function properly.
Best regards,
Günther.

This is how my first faulty mass airflow sensor (MAF) manifested: the engine accelerated slowly, and just above 2000 RPM, the wheels would spin, even in second gear.

"What does the error memory contain?"

Hello Reiner,

The error memory doesn't show any error messages, which is why my VAG mechanic was also at a loss.

Greetings.

Andi.

Hello gwg,

Yes, my TDI has a variable turbine geometry (VTG) turbocharger.
"Some time ago, I sprayed the rod between the vacuum sensor and the ATL with MoS2 lubricant. The rod seems to move relatively freely and travels about 4-5mm. However, because I don't have a direct view of the rod, it's difficult to accurately estimate its range of motion."

Greetings.

Andi.

Hi.

Quote:

4-5mm

Standard range: approximately 1 cm. It is best to remove the adjustment knob and manually check the adjustment range and the adjustment knob itself.
Do not disassemble the VTG (Variable Turbine Geometry) rod unless you have a VAG-COM diagnostic tool and the time to do so, or if you make precise markings of the rod's length beforehand.

Oil should not be mixed with ATL (presumably a type of lubricant) to create "oil coal" – this is bad. If you need to use anything, use copper paste instead.

Best regards, Rainer.

Hello,
If the VTG adjustment can only move halfway, then the ATL is already quite 'trimmed,' and cannot respond as 'dynamically' to demands anymore.
As a result, the engine takes in air more slowly, which also causes it to react more slowly.
If the error isn't too large yet, the Automatic Traffic Light system will likely be able to provide enough extra time later on, but it will do so at a slower pace.
Best regards,
Günther.

Hello,

Meanwhile, I visited the VW/Audi specialist again and received the usual response: no error codes could be read. Furthermore, they suggested that the behavior might be considered normal as a form of torque limitation.
I believe he doesn't take me seriously .
The problem seems to be that the error is often less pronounced when the engine is cold.


I've taken a closer look at the entire error pattern again.

"The problem often doesn't occur or is less pronounced when the engine is cold, which means that acceleration in gears 1 and 2 is still good, but a slight hesitation can be felt. The effect is more noticeable at low ambient temperatures. In other words, if the outside temperature is higher, the problem tends to occur more frequently even with a cold engine."
When the engine is warm, the error usually occurs.
When starting, if you accelerate gently for a few meters and then increase the RPM to around 1500 before giving it full throttle, the engine seems to accelerate normally, and there is almost no noticeable jerkiness in acceleration at 2200 RPM.

When the engine is idling, the pressure sensor pulls on the VGT linkage. The distance it moves could be as much as about 10 mm, but it's not visible, only felt, so it's difficult to estimate.
When you accelerate, the VTG (vertical takeoff and landing) slowly and jerkily descends.

I then tried to disconnect the connector at the solenoid valve, but I couldn't because I couldn't figure out how to release the mechanical locking mechanism. However, the error didn't reappear for a few kilometers. The contacts looked quite new from the back.

However, I noticed that the valve is connected to a pressure accumulator, and its mounting bracket appears to be broken, causing the balloon to hang freely in the engine compartment.

Ski_Andi wrote:

"The problem often doesn't occur or is less pronounced when the engine is cold, which means that acceleration in gears 1 and 2 is still good, but a slight hesitation can be felt. The effect is more noticeable at low ambient temperatures. In other words, if the outside temperature is higher, the problem tends to occur more frequently even with a cold engine." When the engine is warm, the error usually occurs. When starting, if you accelerate gently for a few meters and then increase the RPM to around 1500 before giving it full throttle, the engine seems to accelerate normally, and there is almost no noticeable jerkiness in acceleration at 2200 RPM. When the engine is idling, the pressure sensor pulls on the VGT linkage. The distance it moves could be as much as about 10 mm, but it's not visible, only felt, so it's difficult to estimate. If you accelerate, the VTG (Variable Transmission Gear) will slowly and jerkily decrease its setting.

That reminds me of my Volkswagen Golf 3 from 1997.
He had similar issues with the small series turbocharger, but it was better with a larger one -> technical article about sticking VTG turbos. Unfortunately, there are no more Garrett turbocharger parts available for purchase (officially) anymore .