Saturn 1999 sl Engine has a high idle speed. How do I find, replace, inspect IAC?

Remove air filter, warm up engine, plug the IAC port (the small hole in the bottom of throttle body) the adjust idle screw c/wise or anti c/wise to set rpm. REMOVE IAC plug and check the performance. Good luck.

it sounds like the ignition crntrol module

the iac idle speed air control solenoid

leaking o-rings at the fuel injectors would explain the hard starting when warm-when you hold the petal to the floor, it shuts off the injectors, which will make it possible to start it after the injectors leak down on shutdown. O-rings are easy to replace, just disconnect the battery and pull the injectors straight up to remove, get the old rings out and install the new ones, light lubricate the base of the injectors and pop them back in.

that might explain the high idle too, although usually the idle is not consistent when the injectors are leaking at idle-idle is rough. I would make sure the engine coolant temperature sensor is new (they are very important on saturn, the original one is plastic and they are known to crack easily-the replacement should be brass)-also, check the Idle air controller, best to remove the throttle body (4 bolts) and remove the IAC and clean it thoroughly, being careful not to get the top half wet-sensitive electronics. Clean the post that the IAC goes into, and clean the throttle body (both sides) while you have it out.

remove the throttle body (4 bolts) and then remove the idle air control (bolted to the TB, between the firewall and the throttle body)-clean the TB, the Idle air controller and remove the Throttle Position Sensor (opposite the IAC) and clean it if necessary. The IAC carbons up on these cars, as does the Throttle body-I know, I have a 99 SL with 180,000 miles, it is almost like an oil change as they get older.

high idle concern is probably caused by either a sticking throttle plate, defective IAC or the computer is commanding the high idle for another reason.

the blower motor is found behind the glove box in the HVAC case

Can you explain the shifting problem you are experiencing? Is it a slam into reverse and/or forward gears? Is there any slipping in forward gears?

The idle may be due to a dirty Idle Air Control (IAC) valve or a faulty Throttle Position Sensor (TPS). The first step is to remove the throttle body and clean it with some carb cleaner and get the black carbon off of the IAC and the underside of the throttle plate.

What was the code for the trans? Was it is incorrect gear ratio code or a vehicle speed sensor code?

The engine coolant temp.sensor and idle air control will usually make the check engine light come on if they go bad.If you have high idling then check for vacuum leaks or sticky throttle.

Intake manifold gasket. Leaking where intake meets head.

Did the "service engine" light come on in the dash near the speedometer?
There is a small electric motor located on the throttle plate called an "IAC" motor (idle air control). Its purpose is to maintain the corrrect idle speed when required such as your stop light situation. Occationally the motors "pintal" that controls the idle speed will get stuck in the bore seat and can't control the air flow of idle any more.
It may be dirty and need cleaning or the motor could be bad and gone to the great junk yard in the sky. The electrical connection and wiring should be visually inspected for corrosion or damage near the motor assembly but should not be an issue.
Let meknow what you see.
Thanks,