replaced alternator now it won't idle?

This is on my daughters' 97 Montero Sport with 3.0 V6:

The alternator has been squealing (bearing) for a while and finally died the other day when my daughter was driving back from college. Car cut off when battery was completely flat. Her boyfriend got car jumped-off and they got it home (luckily wasn't but 2 miles from home when it died) I got home, jumped the car off and checked voltage at battery and it was about 7 volts. I don't even know how it was running! Anyway, pulled alternator and replaced with new one, charged battery and now have good charging voltage at battery when running (14 volts) Anyway, NOW the car won't idle. runs fine as long as you keep your foot on the gas but take it off and it shuts down. The car has done this before when I had to replace a battery terminal and more recently when I replaced the battery several months ago. It wouldn't idle at first but after driving for a little while, the computer "reset" or "re-learned" and was fine. I assumed that was what was up with this but it has been 5 days now it it still will not idle. Don't know if this is relevant or not but my daughter informed me this morning that the tachometer seems to be going crazy also! Said it just wanders all over the dial sometimes.

By the way...................The Check Engine Light is NOT on.

Any help appreciated!!!

Ernie

is the small wire that goes to the starter on there tight? or maybe they gave you an alt for a different sub model/year...only two things I can think of, but I'm betting it's a loose wire.