Expert solution needed !!!!!!!

[BigZ24]

my car (1988 z24) run 3000rpm idle speed! this is the problem! the motor is my old 2.8l whit piston and crankshaft from 3.1l so now its a 3.1! i try lots of thing! first i make a relearn idle, i change the IAC sensor, i change TPS sensor, i change IAT sensor, change the MAP sensor, i chec the vacum line from the MAP and the TB's, i change intake gasket for new one, i change TB's gasket to. a GM mechanic and he told me to try if the booster brake valve are broken by loosen the vacum line. but the engine still run 3000 rpm and the engine soon light up and if i try to pull out some problem code by putting a juper wire on the A B terminal the ecm flash a 12 code (ok engine no problem) but the light is on when the car run! oh and yes when the car run normaly hot (105 degre) it still run between 1000 - 1500 rpm !!! SOMEBODY CAN HELP PLEASE!!

and if you dont very understand my english its cause i'm french and i come from montreal....so y try to speak english!

[geoffinbc]

Turn the car on an jump the A&B pins on the aldl connector. Do not start the motor. This should drive the IAC motor all teh way closed. No un plug it and start the car. Is the idle lower or do you have to step on the gas to get it to stay running? If so then you now know your IAC is opening up way too much.

The next thing to look for if it is not that are vacuum leaks. Remove all vacuum lines (including the brake booster) but NOT the MAP sensor. Plug every port on the manifold and on the throttle body. Start the car now. If the idle is lower you know one of thoes vacuum lines has a leak.

[BigZ24]

start the car whit a jumper in A&B connector will not damage de ecm ????? and i have change the IAC for a new one from GM so i believe it can not be the problem

to be more specific...i strat the car..it run at 1500rpm like it supose to be when he was cold 5 seconde after i strat the engine soon light up and after the rpm start to going up slowly to 3000rpm ! so i am busy cause if its a vacum leak or IAC problem the rpm will not going up like this !

[geoffinbc]

It could be the IAC. Or the command to the IAC motor. Do what I said and jump the A&B pins turn the key on and listen for the IAC motor working. Give it a few seconds to close all the way. Unplug it and pull the jumper out of the ALDL connector. Now start the car. With the IAC closed and the plug removed you can either eliminate it as the problem or verrify it as the problem.

[BigZ24]

i try what you tell me and notjing goes better! so i decide to take a ride to looking for what can be bad ? on back home road the temperature gage go really hot..arrived at home I turn off the car and listen the coolant boil in the overflow box ! so it probably be the thermostat or the coolant sensor.... but what I really asking myself is if its possible that the coolant problem could be related to my idle speed problem ???
cause the engine soon come on and off when i drive an the idle seem to be OK some time and some other time he goes up to 2000rpm!