Constant speed Every now and then all lights flicker and the speed will vary.

https://www.youtube.com/watch?v=hAVABiCe6ew
If your light bulbs are flickering, turn off the power and using a glove to protect your hand from heat, screw the bulb in tighter. Loose light bulbs mean the socket isn't making proper contact with the bulb, and that can cause intermittent flickering. Even recessed lights can loosen, so check those connections first.


https://www.cnet.com/how-to/flickering-lights-check-these-common-culprits-first/

Low oil pressure maybe? Oil pressure will vary depending on engine speed-higher speed=more psi, lower speed=less psi. If there is a mechanical reason for low oil psi then idle is when it will be low enough to turn on or flicker the light. Also, you could very possabily have a slugged up oil pick-up screen.

The Kitchenaid uses a centrifugal switch to maintain a constant speed. This must be sticking to cause this. You mixer will need to be disassembled and inspected.

possibly a stuck switch for the hi/lo relay

It could be the idle sensor. If your check engine light is on, get the codes. It it is the IAC, it will pick it up.

You could have a bad head gasket. If the coolant isnt leaking on to the ground, or visible inside the engine comparment, then it is leaking into your engine and mixing with the oil.

It sounds like the motor's going bad. I suggest replacing the motor or the vacuum, depending on the condition of the rest of the vacuum, and how much the service center charges for a new motor and service.
If it's an older vacuum, there are probably additional items showing wear and tear. This would make it more feasible to purchase a new vacuum.

Most likely this is becasee motor driving the "tinsel in a stick" is not working. Take the glass off, remove the fake logs and look underneath to see if the the rod wih the tinsel is turning. If not the problem could be the motor or the speed control. If you have a voltmeter you can test the speed control output - it's 12VDC - of course it will vary depending on the speed sselection. The mot probably cause is the motor has died. You can buy a new one at www.ibuyfireplaceparts.com. Cost is $77.01> it's a bit tricky to replace - just a tight spot is all - 2 small screws and out it comes.

I am not familiar with your specific model, but varying speed is usualy the first symptom of a bad belt. Look at the drive belt. If it seems kind of loose ( there should be some stretch, but it should also snap back quickly), it may need to be replaced.

Try that first. If that does not resolve it, let me know and we'll look further at other possible causes.

Dan