Had a new experience about 3 weeks ago, could be a month.
Went up to Steve's in Shropshire, with all the traffic and accidents, the trip took near enough 6 hours, the car performed flawlessly, but then i never got a chance to press the pedal down much.
When Steve took the car out for a test the rev counter would stop dead at 3500 rpm, the immediate conversation was the 123 limiter which Steve could feel cutting in.
Being that the 123 is the bluetooth version I started the app and checked the rpm to the dashboard, car showed max 3500 but the app was showing up around 5000 rpm, which is consistent with the 5800 rpm limit I had set, and I said it must be the rev counter, which I can swap with the spare.
There was limited time in the day for other works, so we left the problem to look into some other time, and I drove back in the evening, again 3500 rpm was the max, fine for keeping within the speed limit on the motorway, all smooth.
Been looking into the problem this last week and noted the car would do 4000 rpm in a standstill position, and the app showing 5500 rpm.
This is not consistent with when the car was on the rolling road or subsequent drives, so the timing gun was brought out, showing 11 btdc, but showing 6000 rpm when the car dash is indicating 4000 rpm and the 123 limiter cutting in ( I did up the limit to 6000 rpm ).
The car engine feels like it is at the upper limits.
I checked the dizzy cap and rotor, all good, fuel lines secure, HT leads firm, throttle linkage fine, rev counter and dash leads confirmed, coil leads checked, earthing good, not much else has been touched.
However, having traced back to things done, only the Iridium spark plugs were changed to normal ones, put a new set in, and all is back to normal with matching rpms across all three displays.
My only regret is not checking with the timing light on all the HT leads for a pinpoint of the problem, binned the plugs.
Also it seems the 123 was showing correct readings at the dizzy and the car dash at the coil, and the timing light on HT 1
One of the spark plugs had failed, but only at high revs, all I know is
without the limiter i could have caused a lot more damage in testing.
Has anyone experienced/diagnosed similar ?