Intertherm furnace short cycling

[azindy]

Furnace: Intertherm MGHA-056ABFC-02
Blower: Mortex 87-1008-34A
Gas valve: Robertshaw-Grayson 7200ERCS-1

Hi!
I see this is a fairly common problem, but that the diagnosis depends on certain factors, so I hope I am not being redundant by starting a new thread.

My furnace pilot stays lit. The furnace burner comes on fine. During the short cycle, the burner remains lit and the fan/blower is what appears to be kicking on and off. The on and off cycles can last as little as 30 seconds.

All vents are unblocked and have air flow. There is suction at the intake. The squirrel cage is not perfectly clean, but only has a light film of dust on the blades. They are not "crusted over" and not rounded off.

Any help would be GREATLY appreciated. I cannot stand having the furnace turned on anymore. It drives me crazy, and I am sure it is harming the system.

Regards,
Eric

[azindy]

Fan limit switch...?
Run capacitor?
DeLorean Flux capacitor?

Any ideas...? Anyone...?