1200 RPM, no throttle connection..help please.

fritz

370Z M6 2010
Two months from new at 4100Km it limped to 1200RPM max, with no power/accelerator response: It took a dealer two weeks to fix a "relay" and car was great until aprox 8200Km (a 4100 Km coincidence?).

Today, when at 2000RPM in 5th, it slowed to 1200 RPM max/no power..same as before......and it reads the same 3 codes as last time.
P0300: "Multicyl misfire"...but there's actually no misfire to an experienced mech. It idles dead smooth (just like before) at around 1000 RPM but won't go past 1200RPM in neutral.
P1090 VVEL ACTR MOT-B1
P1093: VVEL ACTR MOT-B2

On the first occasion (1300 Km from home)..... Nissan had me pay the bill and ducked paying me.....but wrote on the receipt that it was warranty work.

The car (and Nissan warranty !) is now proven untrustworthy. Is there any-one here who knows of this engine problem?

The only clue is that the short fuel trim, S-FUEL TRM-B1 is 87% and for S-FUEL TRM-B2 is 120% ...Is that enough discrepancy to cause this problem?
(L-Fuel TRm is 101% on B1 and 102% on B2).

It also knocks a little before firing when cranking.....just like last time at 4100Km..the accelerator pedal again seems almost disconnected.

No other problems...No oil consumption or excess temperatures.

Any suggestions would be very much appreciated.