Idle or Power Problem?

[duendeverde]

I have read a lot of threads about idle but never seen anything related to my problem.

My car without the A/C on idles at 600 rpm, when the cooling fan kicks in the rpm goes up to 800-900 and then to 600 (when the fan turns off). When the fan turns off, the rpm idle at 600 and the engine vibrates a lot until the fan kicks in and goes to 800-900. It does this cycle over and over.

I did some troubleshooting:
With the A/C on and lights On the vibration goes away (idle at 650-700 with fan off and 800-900 with fan on)
With the A/C off but the lights on the vibration goes away (idle at 650-700 with fan off and stays pretty much the same with fan on)
With the A/C off and the lights off the vibration occurs (idle at 600 with fan off and pretty much the same with fan on)

Could this be something related to power?

The last changes i made was cleaning the throttle and changing spark plugs

Thanks in advance