Do the 2 cooling fans on the radiator come on at the same time or staggered. Ive got one working & one that doesnt. But before I go looking for a problem I figured I would ask.

1 is temp. controlled, other is AC on/off controlled (& possibly high temp controlled as well, I'm not sure).

Like Stephen said, passenger side fan is turned on by a Fan temp switch and the other is turned on with the AC system. And some say that the same AC fan also comes on at Very high temps (like 238*), this I'm not sure about. To help keep my temps down I hooked up a manual flip switch inside my car, to turn it on (2nd Fan) when ever I want...Alot of info that will help You is in other threads ("fan switch", and "Overheating issue") Read post # 17 on "Overheating issue" that may help.

On an 88 IROC (assuming TPI, since dual fans are mentioned) the primary (passenger) fan is ECM controlled to turn on at 220°F.

The secondary fan is controlled by the fan switch in the passenger side head and turns on at 238°F.

While I'm not 100% positive of the transition year, in '87, the ECM turned on the primary fan only, when the A/C was on. In '89, the A/C would cause both fans to run.
'88 may, or may not, call for both fans to run with A/C but, as a guess, I would wager they should both run.

IIRC, Wiring color at the fan switch would tell you. Dk green would be a single fan runs with A/C. Grey, both will run.

Either way, under normal operating conditions, the fans don't run at the same time.

Yes the car is a 305 TPI car.

Cool. That helps a bunch. Ive only got one fan kicking in at about 225 & shutting off at 220 or so. Oddly it is the drivers side fan. The passenger fan I have not seen run.

I havent checked if the ac turns the 2nd fan on or not. Havent used the AC in a couple years.

That's not 100% definitive, that's just going by what's been stated by others for the fan that usually runs.

I always thought my drivers side fan was the primary on my 87 but, it's been so long since I've rewired it, I forget. It shouldn't make a major difference which runs though, as long as one (the ECM controlled) runs when it should (roughly 220°.. give or take a modest +/- % if going by the factory gauge).

I've done some extensive wiring on my 88. Deadbird is correct on his statement. They are staggered on. One via the ECM the other via a thermostatic switch on the passenger side. I had the same thing happen to my car. If you decide to troubleshoot it and would like a little help just message me and i'll tell you what i did to figure out where the fault was.

you just want More CFM pulling. to do so with stock parts is easy..

just Piggy back the 2nd fan to the first one.. you do not cut any wires.
just use a splice piggy back and.. up grade the fuse just a tad..

it's easy and works better them GM intended...

you can feel the air at the back of you car moving..

keeps it cool in the summer... kicks on when it's Hot and off when it's cool.

That is terrible advice. The fans are also powered direct to the battery and protected with a fusible link, not a standard fuse.

it's been 15 years ago i did mine..so i could be wrong about the fuse... have to look and see.. but i can tell you. setting it up to run at the same time. works just fine.. no probs at all..and the fans come on and go off just fine.....and i did not have to Cut any wires..

For details, check my signature.

As for same time or staggered, the answer is.....both. Here's the deal. On my car, I have a 200/185 fan switch on the passenger side. At the moment, I have the stock GM chip in the car. Now in this situation, you would think that the passenger fan would come on before the ECM controlled driver side fan. But they both turn on at 200°. So it appears that the passenger won't come on without kicking on the driver side if it's not already on.

Your passenger side fan probably does work. It's ultra rare to get it to turn on with the stock fan switch and the A/C off. The car just won't get that hot, that the stock fan switch turns it on. Especially in NH at this time of the year.