Speed fluctuations (suspension) in idle mode

Hello dear forum,

have a small question (I'm on my way and have no RLF and no diagnostic tool at hand):

Can you map the LMM - does the V8 run without?

HIntergrund is: When I started it after 2 weeks in the garage, he didn't want to keep the idle and went out - if you hadn't helped with the accelerator. After a little "pumping" he had caught himself and ran around idle. Interestingly, when he was then at operating temperature and I stopped, he had sporadic fluctuations around approx. 150 - 200 revolutions and felt like after misignition (brittle).
I was at my place before about. 7 years times the LMM was defective and this had become so noticeable - therefore I suspect it. If it were the speed encoder, the V8 would not even start after my memories. even just go out if the giver delivers totally wrong values. Was with me once high-impaired the part from 100°C temperature...

Which sensors could I (simplely) pick up for testing?

Thank you!
Best regards Robert