I had a very nasty tick in my engine after doing a bunch of work to it, I just redid my chain tensioner which went a long way to fixing it, then I found that spark plugs could cause a tick, so I tightened them. It fixed the problem.
However, the reason for this post is that I'd like to understand why the car behaved how it did (both the ticking) with loose plugs, and also it idled really high after tightening the plugs.
When we tightened the plugs down I started the engine and it really struggled, then revs shot right up I had my hand on the keys (didn't see tacho) but figured it was very close to red line (and still going up) so I cut it. When I restarted it sitting in the car the revs sat at about 2k for 3-4 mins, putting it in gear dropped it to normal (ca. 900 rpm) putting it back in park put it back to 2k. After 3-4 minutes it dropped the idle down.
Now I've restarted it three or four times since and it's behaved normally. I figure it might just have been the ECU learning new tolerances but I'd like clarification.
The vehicle is a BMW 740 with an M62 motor.