Well I've searched and saw some similar problems but couldn't find anything specific or mentioning that the car stumbles right before the fan engages.

Car:
1991 Firebird 3.1 v6 (stock)

Recent replacements prior to symptoms (about 2 weeks):
-CTS
-O2 Sensor
-IAC (adjusted by haynes manual)
-Fuel injector o-rings
-Alternator
-Belt Tensioner pully/spring unit

Symptoms:
The car will start fine from a cold start and work well, then all of a sudden the idle will start surging, engine sounds like it's misfiring, and then will die if I don't give it gas. Shortly after the car surges the fan turns on even though the car is still cold. If I start it up again, I have to give the gas pedal a depress when cranking and hold it till the car maintains itself. No codes show, even after running the car for at least 15 mins while trying to drive it around. It appears that once warmed up near 180* (via gauge) the car will act fine until it cools down again.

I figured the fan engages because something is prematurely grounding the fan, either the ECM or some wire. I've looked around the wiring coming from the CTS and don't see it grounding. I'm suspecting the ECM might be grounding prematurely. Is there a way to test this?

 

look at the A/C pressure sensors, and A/C switch.
It sounds like the A/C compressor is tring to kick on, but the IAC does not compensate by opening up.

To verify, remove the plug to the A/C compressor, there-in removing the electrical supply for the clutch to engauge.

also, check on which fan is actually kicking on... pass side... A/C...

 

Thanks, I'll check if the A/C attempts to engage (though the AC is set to off ) when the car begins to stumble. It's a single fan setup though.

 

Yeah my 91 3.1 Camaro does the same thing. like stumbles when the fan came on,..,

Whats this about haveing two fans?? this is new to me., where is the second one? or are ya talkin bout the 3.1's with duel fans?

"Lets nip this in the bud i dont like to hear my ride chockin like that anymore.,lets figure it out and stop it lol once and for all and when others do a serch in the future thell find this post"

then thell see this post of me talkin bout the future .,,.and that would realy be weird haha:

 

I did not see where he said what year the car was, so yes I was talking about 90-92 dual fans. One auto kicks on if the A/C is on, or if it is triggered.

otherwise, the description under the name says 305, where as I have no issue helping a V8 guy, this is the V6 section... maybe he figured out we like to help out people...

 

That's why I put the section of
"Car:
1991 Firebird 3.1 v6 (stock)"

 

then I was on it anyway...