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Q: Accidentally ruined ECM reconnecting battery with ignition switch on

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Accidentally ruined my ecm by reconnecting battery first while ignition switch was in the on position I checked the right side underhood fuse panel the ecm fuse and other fuses did not blow and the interior fuse panel all fuses are good I switched on the ignition all lights and horn and turn signals do work the battery is fully charged the fuel pump does prime when the key is in the on position the car starts up but without stalling if my foot is not kept on the accelerator....would both the ecm and prom have been destroyed? The ignition system module and coil assemblys are ok

My car has 3000 miles.
My car has an automatic transmission.

From what you’ve described, you may have hurt the ECM when you did this but at least it starts. You may be able to test the system to see if the idle air control valve is the faulty component that got damaged. I suggest having the system scanned and tested first before condemning the ECM. Other components may have also been damage when this occurred. If you’re unable to pinpoint the issue yourself yourself, have a certified technician, like one from YourMechanic, perform these checks and diagnose your electrical system firsthand.

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