To meet increasing tighter emission levels and improve engine efficiency, manufacturers have had to develop their petrol engines with direct fuel injection. The one downside of this is, the fuel is no longer injected into the inlet manifold and onto the back of the valve. The result of this is inlet valve carbon build up, which has become the curse of the modern direct injection petrol car.

This Audi RS4 (Possibly my favourite car from the VAG range) came to us with a poor idle (misfire) and lacking the performance you would expect from one of these V8 engines. After some diagnostic time it was clear there was a random, partial misfire at idle, but compressions were good, ignition looked perfect on the oscilloscope and individual injector flow rates looked equal. These information, combined with monitoring of fuel trims etc, lead us to believe this car had carbon build up on the back of the valves, which can disrupt the air flow and therefore the swirl in the combustion chamber, which is critical on these engines.


On removal of the manifold (not a small job) it was clear there was an excessive level of carbon build up, not the worst I’ve seen, but certainly significant enough to give trouble.


Almost there, after initial removal of the heavy lumps the Tunap valve cleaning system is used to clear the carbon by blasting it with a polymer bead.


After a little more blast work the intake port and valve is like new. The Tunap system does an excellent job. Just need to repeat this another 7 times.

The Tunap system connects to a vacuum cleaner to remove the blast media and removed carbon during the process, once its complete there is a neutralising spray used to dissolve any leftover blast media, making it easy to extract and completely harmless to the engine.

After some manual cleaning of the manifold, the car was reassembled and road tested. All data was now correct, idle was smooth and performance was restored.

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