ACCELERATION

[penhosky]

I have a 2010 Panamera 4S with 265k miles. Not long ago it developed the following problem. Upon acceleration it hesitated badly, would not go much faster that 40 miles an hour and ran very rough with every warning light on the dash going off. When I checked codes, it indicated misfire cylinders 5 and 6 so I replaced those coils (spark plugs were done a few months earlier). This fixed the problem... until I tried to accelerate and the same thing happened.
Check engine light said cylinder 4, so I did that. Same thing again, with check engine light... but not code!! I had it looked at by my trusted mechanic and he found the oxygen sensor bank 2 faulty and replaced it but although it ran ok, the check engine light kept going on... no code, but when I tried to accelerate and pass a car, back to the same thing as initially except worse, driving at 30 mph with flashers on.
As I was trying to get home and stopped at a light, I thought I would give it a break and put it in Park; when the light turned green it would not go into Drive, I forget the exact message, but something to the effect that this was to protect the car.
So... I called for a tow, and decided to shut it off, and just out of curiosity restart, and lo and behold it started and ran fine, no lights on the dash, etc. It ran a little rough at first, but otherwise whatever speed it did fine. Cancelled the tow.
Not pressing my luck, I drove to the mechanic, and long story short, after three weeks, unable to fix. And now I drive it as if nothing happened... except I can't "mash" the accelerator. I other words, I can do "normal" accelerations, but not "performance accelerations. I did not notice anything weird about the shifting, although I did not try manual.
By the way, the only engine problems I have had were two thermostats; one under warranty at 40K and the other at 160k.
It has been a totally trouble free car otherwise.
I thought I would put this out on the forum before I succumbed to the dealer (and who knows if he can figure out... something for the infamous PIWIS?). Any thoughts appreciated.

[dr bob]

On another not-Porsche car, this happens when the timing belt jumps. It's usually not too difficult to pull off a couple belt covers over the cam gears (really sprockets...) and make sure the timing marks line up. My familiarity is with the fifty-years older 928 engine, but the concepts have actually aged quite well. Certainly worth a look before going under someone else's knife.

[penhosky]

I appreciate that. Will run it by mechanic. I really appreciate your input.