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Old 11-29-2021, 02:24 AM   #9
Total Buzzkill
Join Date: Nov 2016
Location: OR
Posts: 3,116
Vehicle: '90 D21 4cyl 5spd 2wd
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Don't let the magic smoke out of the ECU. If you do that it'll never work again.

The truck runs, right? Don't rule out the possibility that you might just have a dead LED in the ECU. If you can put the ECU in the appropriate diagnostic mode the check engine light should still flash out the codes. The difference is you would just have one flashing LED instead of two as it cycles through the various diagnostic modes.

Whatever you do, don't mess with the idle adjustment screw or any of the other screws on the throttle body. That'll just create a problem where there wasn't one before (ask me how I know). If you find you're having to read error codes frequently you can make a blinky light box thingy to interface with the ancient data link connector under the dash. It's pretty simple to make one, all you need is a momentary pushbutton switch and two 12V LEDs.
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