Another hint in favour of the Pawel hypothesis is the idle regime:
- as I've written before, the car's engine has been completely redone, in a way that seems excellent
- prior to that, in 2015, the FIP was checked and calibrated by a specialist in Paris
- when the engine renovation was finished, the car was put back together by an excellent mechanic (who was not an MB specialist however); although the PO did things very well, I would say that the term 'no expense spared' does not exactly apply; it was very well done, but there was some small pressure or constraint to keep the amount reasonable (altogether, it still cost close to 20.000€ in 2019, of which ⅔ or 12.000€ just for time spent putting the car back together, including fitting new engine mounts and subframe parts); despite this, there were some small mistakes made, of which I caught 3 so far (missing bolt to secure the air filter box, which obviously fell in while the guy was putting it in, and which he left in the well below the airbox for me to find later and put it back in, wrong wiring in the TTS (G and W wires exchanged), and wrong program dialled into the new 123 Distributor, as well as wrong timing of the ignition (not enough BTDC at idle)
- now that I have had the car for a little bit more than 6 months, working out one (small) issue after another and breaking in the engine, I find that it runs extremely well, especially after setting the distributor and ignition timing right of course; I'm still not 100% happy with some transitions, such as when the car coasts in low regime (1.200-1.500 rpms), when the accelerator is neither depressed nor at rest (just giving it a sliver of fuel), where it seems that it is somewhat starved (there are oscillations where the car clearly needs more fuel to run smoothly), when going down an incline at slow speeds, where there is some backfiring (I think this is what you call it), muted explosions in the exhaust, (the fuel cut off solenoid is not activated, even though I checked it is working and the relay as well; must be the switches on the gearbox, that I will address in another time frame) and some such minor stuff, but altogether it gives a very convincing performance of being strong, in overall excellent shape, and not badly tuned at all (not boasting of my performance, as I had nothing to do with it except for the ignition)
- having said all that as an introduction, at idle, the engine sounds absolutely as it should, easy and at rest, strong and quiet, calm and even, but the tacho says it is running at 1.000 rpms instead of 800 rpms since I adjusted the timing (and I haven't done anything about that yet)
- the maths is very close: 4.325 rpms instead of 3.475rpms for 100km/h yields an 'overclocking' ratio of 1.24, and the 'above normal' idle ratio would be 1.000/800 = 1.23, identical if one takes into account all the errors in the various measurements and estimates.
I'm obviously putting too much stock into my idle regime impressions at this stage, but it is a tantalizing idea, that once again, it would all be 'much ado about (almost) nothing', a false tacho reading, while all the time the car has been absolutely fine and I can soon roar down the highway in full pursuit of Peter and consorts
I can't wait until Monday to find out if this is the (easy) out on this one.
This then begs the follow-up question though: what could cause the false reading of the tacho?
