High idle will not lower

The first thing to try is to get a can of throttle body cleaner from Autozone or Walmart and clean the throttle valve and the idle speed control valve, they get get gummed up and that causes the annoying stall.

Hello, the first thing you need to do is check the throttle body bore for carbon build up. pretty common to have the the throttle body build up carbon between the throttle bore and throttle plate causing some unstable idle problems. you can clean out the throttle body bore with some throttle body cleaner and a shop rag

CHECK OR REPLACE ALL VACUUM HOSES.REPLACE AIR FILTER,REPLACE FUEL FILTER,CLEAN FUEL INJECTORS WITH A CAN OF SEAFOAM TO 3/4 TO FULL TANK OF GAS.CLEAN THE THROTTLE BODY THROTTLE PLATE.SPRAY CARBURETOR CLEANER INTO THROTTLE BODY BREAK CARBON BUILD UP AROUND THROTTLE PLATE AND SPRAY CARB CLEANER AROUND THROTTLE BODY SHAFT AREA REMOVE CARBON BUILD UP TO PREVENT SHAFT FROM BINDIND.BECAREFUL NOT TO GET CARBURETOR CLEANER IN THE IDLE AIR CONTROL VALVE AND OTHER ELECTRICAL PARTS.REPLACE ALL VACUUM HOSES ON THE INTAKE MANIFOLD AND REPLACE PCV.

Your ad is showing 2 different years in it. If it is an 89, there should be an IAC which stands for idle air control in your throttle body. You simply unplug the wires and then unscrew it out of your throttle body. Inspect it for crud build up on it. Look in the hole that you took it out of and inspect it also. You can spray carb cleaner in there to help clean it out. Re-install the IAC and see if it makes a difference. You may have to replace the IAC with a new one. Also make sure your butterflies are closing on your throttle body. You can spray carb cleaner in it also to help clean. Also you can spray some on a rag and wipe out around where the butterflies contact the throttle body.

If you have Coil- on -Plug you haven't found the bad one yet

Your not always going to get a code that is correct
e.g.PO304,PO305 etc

I would buy the injector from you, as I'm sure that wasn't it,
unless you have an air leak around it

You want no vacuum leaks,a near new EGR Valve,no
air induction tubing leaks

Clean the MAF Sensor with CRC MAF Cleaner

Clean Throttle Plate--CRC Throttle Body Cleaner

You did put anti-sieze on those spark plugs, if not
do so.

How old are the O2 Sensors
More than 80,000 mile,replace the front 2 with OEM
Specific Make--Bosch or NGK etc and not some
cut & splice universal type

There are a few things that you can do, do get it idling correctly, and it's fairly inexpensive.

1. Clean your throttle body with throttle body cleaner, with the battery disconnected. Needs to be shiny. When finished, drive around for 20 minutes or so with all accessories turned off, so the computer can relearn the newly cleaned TB. About $7 for the cleaner

2. Replace your spark plugs with A/C Delco 41-103, will idle better with this plug. Around $7 ea
3. Replace your upstream 02 sensor, the one right after the exhaust comes out of the engine, easy to replace. Between $67 and $80, try to stay away from Bosch.
4. Replace your fuel filter around $15 or less.
5. Check your vaccum lines for leaks.

Start with the simple and replace the fuel filter and clean your throttle body with throttle body cleaner. Make sure you clean the passage ways to your Idle Air Control (IAC) valve in the throttler body opening to try to clean your IAC also.
Thank you for using fixya and good luck.

do a compression check on the engine, and replace the bad sensor, i take the throttle body off to clean it and some sensors are touchy about cleaner, i fear maybe something got on the egr valve pintle

The idle is electronically adjusted by the ECM with the IAC (idle air control) valve which is located in the throttle body. Then the IAC get's to dirty from carbon build up, it can cause what your experiencing
Start with cleaning the throttle body, paying attention to the IAC passageway to try to clean the IAC. If this does not fix the issues, you may have to replace the IAC if it is to dirty to clean.
Thank you for using fixya and good luck, do not use carb cleaner, the carburetor cleaner is to corrosive to the gaskets used on the throttle body's. .

Check the engine mountain rubbers ,, one or more of them is broken and needs to be replaced.

pop the hood, start the vehicle and move it from park to drive to reverse with the brake pedal down and you will see the engine moving. the broken mounting rubbers are the cause for this.