I was on vacation with my 93 27 fever last week and it started to idle inconstant, fist it would not idle down past 1500 rpm (tough in the no wake zone) then after I came down from a plane after a hard run it died then it would idle at 500 and wouldn't start without putting the throttle a little above an idle then it would start. Does anyone know if there is an IAC Motor( Idle air control) on a MPI. Any suggestions are appreciated. Then I was have the warning buzzer (temp) going off. I just replaced the raw water impelor last week. It shows about 1PSI at idle and goes up to about 15 when running, it would cool down if I put it in neutral and idled it up. This is a closed cooling system.

THERE IS IN FACT. remove the throttle body. remove the i.a.c . clean the throttle blades,throtle body, and the air pasage underneath the i.a.c . also there is a m.a.t(manifold absolute temperature) sender that tends to get cruded out from inproper winterizing.
as far as the temp issue try a stat. back flush, and make sure you dont have a case of bravbo fever.

good luck

What He said.. Most common.

Here's my question-did you find all of the pieces when you did the impeller?? If not, there may be some stuck in the oil cooler that are blocking water flow-backflush them out if so. It does sound like your IAC is sticking- I have one doing it now too, gotta get time to clean it or replace it.

I think I got all of them but there were a lot of little pieces I will try a t stat and backflush