MAP reads absolute pressure which is what is important for fueling properly.
You might have something else wrong. When I bought my 97 out of TN, the gpr was bad and it started just fine down to about 45-50°F. The IDI on the other hand, that is not surprising.

 

Oh, it'll *start*. It'll just crank about two-three times as long. There's nothing wrong with our trucks; they both start with aprx. one second of cranking after the WTS light goes off. (Well, the RC truck is cranking a little longer because it's overdue for an oil change, but I digress...) Shoot, it should start down to 25-30F, provided you crank it long enough. Just depends on how frequently you want to replace the starter.

And of course, the GPs aren't just to start the engine. OTOH, efficiency is probably not one of the OP's priorities....

 

I have my '96 glow plugs on a switch. The truck gets used only for plowing my drive in the winter and it sits in the shop at 50°. I hop in, hit the key and it instantly fires up at 50° with no gp's, and idles perfectly.
It sat outside this winter for a few nights in the -25° range, switch gp's on for about 10 seconds and it cranked a couple rotations before firing up. I was impressed to say the least.
Motor has over 260k miles on it.
Every motor is different, it's up to the OP if he wants to mess with the gp circuit at this point.


....And the gp's ARE just for starting. What else would you need them for?

 

Per the FSMs, they provide additional heat on startup for more efficient burn. That's why they run for up to two minutes, and why the run time is pre-determined based on temperature (and not directly controlled by temperature). 'Course, that may also have been programmed in anticipation of Big Brother EPA eventually nosing in, and again, most likely not on the OP's radar....

 

Oh, right, emissions, just like the back pressure valve we always delete.....

 

Yeah, I suspect the extra burn time for the glows is related to extra emissions control. I've got a switch for mine, and the batteries are so happy when I cut them off short.


Regarding the auto-deletion of the EBPV, remember that it's a built-in exhaust brake too. Ford missed the boat by not adding a couple of switches and being the first on the market with an exhaust brake. It's very, very useful towing in the mountains.