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1991 911 C4 valve noise, cling noise

Engine

Vehicle Information: Year: 1991; Body Type: Coupe; Total Mileage: 81000;

2 months ago, I bought a 1991 911 C4 with 79,500 miles. I got it inspected by a Porsche shop and everything was in perfect shape except a little cling noise (just like I am using low octane fuel) from the valves (only under full torque demand and 4000 RPM). The owner said that the car was in storage for 2 years and he probably ran the engine with water in the tank. They purge the tank and the mechanics recommended running a few tanks of gas with additives to clean the system before considering valve adjustmentIn 7/16/02, valves were adjusted and the mileage was 77,600 (only 2000 miles since last adjustment). In 3/04, they replaced all spark plugs, both rotors and 1 distributor cap. Since then, I drove the car 2,000 miles (1,000 back to Wisconsin!) and I am still hearing the ping under full torque demand and around 4000 RPM (your response to the question on gasoline octane describe very well my problem). I used 2 heat additives plus 1 injector cleaner additive. I also noticed that the distributor vent kit has not been installed. The car doesnt leak one drop or smoke. I always use the highest octane available. What are your recommendations and in which order?Is there a simple way to inspect spark plug wires?I am considering: 1) running a few more tanks with HEAT additive, change fuel filter, spark plug wires, distributor adjustment and valve adjustment. I am also planning on adding the distributor vent kit as soon as I get your answers.PS. This is my 1st Porsche purchase and I have been dreaming about this car for 25 years (since I was 12!). This is the only issue I have and I am in love with Porsche!I want to thank you in advance for your help. I really appreciate your assistance.

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