My 98 C70 coupe had this problem for 11 years each smog inspection I would clear the code by disconnecting the neg cable on the battery This year I replaced the gas filler neck ($45 used) because I noticed that when I removed my gas cap there was gas on the rubber seal which means thats where the le...

I demagnetized the cassette adapter and the problem went away

The sound is like buzzing that comes and goes, so it might be a bad spark plug?

This only happens when I use the cassette adapter

When I connect my cassette adapter to my iPhone for hands free operation, I've tried demagnetizing

As my post stated my TPS is 19 yrs old but I really think that the Turbo intercooler intake hose was really the problem, if yours is like mine was soft and deteriorating that most likely is the problem, this hose connects directly to the Throttle body and it is my belief that time and heat causes it...

The TPS may have been just fine but for $38 USD I'm not upset, the worn and soft Turbo intercooler intake hose was most likely collapsing during hot idle starts and also high acceleration ( also under slow speed acceleration there was a weird humming noise) Since I replace the Turbo intercooler inta...

I now have 325559 miles, I noticed the difference right away when I replaced those two parts.

I replaced the Throttle position sensor and the Turbo intercooler intake hose, the sensor had a lot of miles on it and the hose was just plain soft and badly worn I haven't had any reoccurring problems since

After 11 years of living with this code my local Volvo independent shop Eurotech in Rancho Cordova Ca. 95670, fixed the problem by resurfacing the filler port, word to the wise if you have fuel on your gas cap gasket then your filler port is your problem.