Speed limit issue
 

Folks, I'm trying to understand why my car virtually refuses to go above 83mph. from 0 to about 80 its pretty much a rocket, but after that it takes a whole lot more eeffort to get her to 83, and then she just stays there no matter how hard i push her, kickdown and all. She is well maintained, atf change, performance plugs, new ignition wires, k&N filter, Mobil 1 oil, heck the tranny was replaced late last year. I just dont get it. I know shes a bit old (2000 A4Q 2.8L Auto) with 203k miles on her, but i expected to be able to get to at least 90mph. Am i expecting too much or is there somthing amiss? Honestly, the way she ramps up to 80 and then just freezes is wierd. I thought the speed limiter was set to 135.

Codes?
Done a throttle body adaptation?

Does it shift at redline (6200) at wide open? What happens if you keep it in third or forth?

No codes....
 

..., yes did the trottle adaptation. She will shift at red line, but once i get to that 83mph mark, she wont even rev to redline. she revs to around 3000 and just stays there no matter how much i step on it.

What happens if you try to go above 83mph in 4th gear? This will rule out a engine/gearbox issue. Sounds like a speed limiter set to 83mph.

Yeah, i tried that as well, i downshifted to 4th and stepped on it. No increase in speed. It just hangs there (actually its 85mph on closer inspection). Honestly, i'm beginning to think it might be a speed limiter issue, i wish there was a way i could check the limit using a scan tool. Now guys, the most painfull part of all this, is that my arch rivals, the infamous V6 Camrys are beginning to give me a run for my money. There is this five mile long bridge over water that i take to work every day. Its pretty much a race track on weekends or late at night when there is low traffic (no inforced speed limits in my country). I usually hold off or obliterate most challengers without even having to get to 85mph, but for those that decide to go above 85 (mostly the blasted Camry guys) i have no reply cos the car just hangs on me at that point. Oh the shame of it!

Decided to take the car for a thorough hard drive, pun not intended :) When i tried to push her above 85mph, the MIL began to flash, then stopped flashing and went off when i slowed down. Got home and pulled the following codes

PO431: warm up catalyst bank 2: efficiency below threshold

P0300: Random/multiple cylinder misfire detected

P0304: Cylinder 4 misfire detected

P0333: knock sensor 2 (G22): signal too high

It would be interesting if you had another ECU to swap in. Sure sounds like the speed limiter got reset lower somehow.

Honestly, I think that may be an option.
 

BTW, this year i've had two instances where the EPC light came on, and i get the "accelerator position sensor: implausible signal" code. Both times it happened was right after i had the engine steam washed. Both times, the EPC went off after the engine dried off. Dont know if its related to the speed issues i'm currently experiencing.

I'll guess that the knock sensor is improperly torqued or bad.
ECU is fine.