2004 Cayenne S power problems at low RPM
 

Good day.

I've been maintaning my car by changing air filters, spark plugs etc which did result in better performance since the original purchase day (2 month ago), when the car was not doing well.

However, some issues still bother me. During normal city conditions, when I drive 60-70kmh (40-45mph), in economy mode the gearbox shifts to 6th gear. At this stage the RPM drops to 1200-1500 rpm. The car starts to jerk. Engine chokes. Feels like there is not enough fuel, or there is a blockage. The problem goes away after 2,000rpm, when I **** to 5th or 4th gear and the engine runs normal.

At traffic light, especially when I got AC on, the RPM drops further to 700-800rpm, and the engine periodically tries to die, chokes.

I have some concerns:

1) destroyed CATs. Considering that the car has 137,000miles on the clock, and the quality of the petrol, I think CATs are blocked, and does not let the engine "to breathe" normally. I'm thinking eliminating the CATs

2) Injector heads are plugged. There is a high offer to clean the injectors with ultrasonic device. People have positive feedback about this, but on other cars. Never heard about one getting done on Porsche. But, never the less, the injectors are same principles for all cars....

3) Oxygen sensor is dead and does not perform well. Planning to change it

4) Some people say it is the fuel pump. But if it was a fuel pump, it should be visible at higher end of power, and not the lower. So to me it is out of the question.

Also, the car does not go beyond 190kmh (120mph). I got 275/45/R20 tyres and alloy rims. Can it be because of larger size of tyres?


Thanks all for review and feedback.