TBI ISA Adjustment procedure

[eaglescout526]

Straight from the AMC|Jeep INJ. TBI 8980010380 factory/dealer manual

 

Book: text from the book will follow 

Me: suggestions or tips will follow

 

Book: Adjustment of the ISA motor plunger is necessary only to establish the initial position of the plunger after the motor has been replaced. Me: In most cases, it is to fix what the PO or a Shadetree mechanic shouldnt have touched.

 

Book: WARNING: Use extreme caution when the engine is operating. Do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Me: Yes I feel this is necessary to include in the write up as you will be running your 2.5L at 3kRPM.

 

Book: Remove the air bonnet and start the engine. Me: You want to remove the plastic cover for the throttle body like so(not the base the bonnet clips to, this is just an example of what you want to expose):

 

Book: Allow engine to attain normal operating temperature(upper radiator hose hot)

Turn the A/C off if equipped

Connect a tachometer to diagnostic terminals D1-1 and D1-3. Me: Or use your dash's tach or the REM tool from nickintime

 

Book: Turn the ignition off. The ISA motor plunger SHOULD move to the fully extended position. 

Me: If your ISA is not doing this, I highly recommend rebuilding it, all that is inside is plastic gears and grease that more than likely need to be cleaned. If the motor still is not working, the motor itself can be removed to be cleaned but can be tough to do if you are not used to working with small motors. HO scale train motors are great practice motors just as an example. I do offer rebuilding services as well.

 

Book: With the ISA motor plunger fully extended, disconnect the ISA motor wire harness connector and start the engine. Me: Its gonna get loud, please wear ear protection too!

 

Book: With this condition, the engine idle speed should be 3500 RPM (±200). If the speed is not correct, turn the hex head screw (A) on the end of the plunger to provide an engine speed of 3500 RPM

 

Me: Now the next section says to fully retract the motor, you can not do that with it disconnected from the ECU. There was a tool back in the day that you plugged into the ISA to control the motor. Now it says the closed throttle switch should not contact the throttle lever, this is BS as if it didnt, the engine would basically choke on idle and you would end up with a constant rev hunting condition as the ECU will use the ISA to compensate over and over(Now 86 2.5L's might not have the throttle lever touch at all and thats fine, this book was written August of 1986 so it covers 87 and 86 but not what any revisions they did to the 2.5L's of 88-90). Ignore this and achieve your 3500 RPM speed. Shut down the engine or connect the ISA if youre a bit brave to do that while at that high of speed, the ECU should bring down the idle once it is plugged back in. I recommend just turning it off, plugging it in and then starting it back up to watch it operate as it should. 

 

Now put it all back together. Book says once you start it back up you should see the tach read 3500 for a second and then come down, I have never ever seen mine do this, I would speculate that the ECU reacts pretty quick and brings down the idle before it gets that high. 

But this is how you adjust your ISA, do not touch it again once you have done this, if you have a high idle or low idle and the ISA isnt moving, it needs to be rebuilt. If the ISA operates as it should and you have high or low idle, there is something else wrong and the ISA should not be touched or used as "something to get you by" on your daily. 

 

Feel free to drop any questions.

[White_Comanche]

Great write-up Eagle. Thanks for explaining things in granular detail when it was needed. This step-by-step will come in handy for anyone trying to figure this out.

 

Wearing hearing protection during this procedure is really smart. I would include eye protection as well.

[eaglescout526]

1 hour ago, White_Comanche said:

Great write-up Eagle. Thanks for explaining things in granular detail when it was needed. This step-by-step will come in handy for anyone trying to figure this out.

 

Wearing hearing protection during this procedure is really smart. I would include eye protection as well.

Thanks and no problem!

 

As far as eye protection, you can if the wind from the engine bothers you but I wouldn’t expect anything to fly up and out at you.