I’m not convinced of anything specifically without seeing and testing.
I only offer possible causes to look into.
I’ll site you an example:
A friend brought his vehicle over claiming the engine had a shake / vibration when idling.
Personally I didn’t feel it or see it while watching the motor.
But he pointed out if you watch the radio antenna you could see it vibrate.
True enough you could but it was so minor many wouldn’t believe it a problem and the vehicle rode and drove extremely well being 19 year old and had no codes and idled better than many new cars.
But it seemed to really bug him.
He had replaced pretty much everything you can imagine, plugs, wires, distributor, MAF, all filters, new air intake, all new vacuum lines, the list was quite extensive.
He also took it and had the system smoked to check for leaks.
Scratching my head and beginning to believe to believe this just may be the workings of a 20 year old car.
I hooked up a scanner to it and noticed fuel trims were a bit high, but nothing really unusual at idle, but went higher as you increased rpm.
Not quite the trail to a vacuum leak or injector issue I would think.
Went and hooked up my smoke machine and could fine no leaks (which didn’t surprise me considering there were no codes )
Well with everything being replaced under the hood I decided to have a look in the rear.
Now to my surprise after awhile, I stumbled across a crack in the top half mounting flange of carbon canister where the purge valve mounts.
If you were to look at any angle other than directly perpendicular you would never see it.
It was cracked due to the mounting screws rusting and swelling that cracked the mounting flange.
Installed a new canister and purge valve and any sign of vibration was gone.