Working on an 87 IROC with 305 TPI. I had a major brain fart. I was trying to diagnose why my primary fan wasn't kicking in. So I jumped the ALDL into diagnostic mode to see if the fan would kick in. It did. Happy Happy Joy Joy. But then I forgot to remove the jumper from the ALDL and I ran the car at idle like that for about 5 minutes. I shut it down as soon as I realized my brain fart. A few minutes later I fired it up again and it ran like doo doo. Its 3 days later and I finally decided to swap in an extra Bosch MAF that I had laying around. It runs perfectly again. So here's my question.

Can running the motor while in diagnostic mode do any damage to anything? In this case possibly the MAF but what about anything else such as the ECM?
Or was this just a goofy coincidence?

 

Jumping the ALDL into diagnostic mode while the car is running is written in the shop manual. Doing so will allow you to see when the car goes into closed loop. The check engine light will blink twice per second in open loop then will blink once per second in closed loop. But you should not start the car while the ALDL is grounded.