Helping JimT out with an inframe ...

[JimT]

(10-12-2020 )JimT Wrote:  Engine is running ok. Might have an injector acting up, but it's subtle right now.

Guess I should have elaborated a little...

At cold idle it's a little rough, but smooths out as it warms up. Rawze noted this when we first fired it up and there has been no real change since then.

What caught my attention since then is a slight surge, reproducible, typically around 1500-1600 rpm. It's most noticeable with little to no engine load, like cruising down the road and the engine has to do the bare minimum effort to maintain a given speed. It's sometimes present under acceleration, however it's VERY hard to notice when it does occur.

This surge is predominately audible and I can't see any actual change in RPM on the digital dashboard reading. Maybe 10 rpm, if that. It occurs with a constant period of about 1.5 seconds when running about 1500-1600 rpm. It doesn't occur at higher (1700-1800) rpms and I don't spend enough time in lower rpm ranges to know if it applies. It does not seem to occur at idle speed (I'm set at 720rpm).

Some quick searches here led me to this post in reply to this thread. It pretty much matches my situation/symptoms.