Why the rough idle when hi-speed fan is on?

[Fred 86 GN]

Put in a manual switch to turn on the hi-speed fan for extra cooling between runs. When I turn the hi-speed fan on while the engine is running, it idles really rough and acts like it is struggling to run. Anyone else experience this?

Could the load on the alternator cause that much drag? Is this a sign of an alternator on its way out?

Does it act that way because the additional load is not being compensated for by the chip programming?

Thanks,

 

[scottyb]

Does your fan come on high when the AC compressor runs? Does it struggle to idle then also?

 

[KendallF]

If you have the a K&N filter, the fan may be blowing on it and causing enough turbulence to screw up the MAF readings at idle. Try blocking off around your air filter and see if the idle improves.

 

[Fred 86 GN]

I believe the fan comes on when the A/C is on from past experience. The compessor needs charging and I don't plan to use it till then. It did not make the engine run super rough last time I cycled it.

The K&N cone filter is relocated between the radiator and the front grill/bumper. That, along with two feet of 3" piping between it and the MAF should insulate the MAF from turbulent flow when the fan is on.

Anyone know what load (hp) the alternator draws when the hi-speed fan is on?

Thanks,