Mustang uneven idle and error

Those symptoms could indeed suggest a mount failure, particularly with that mileage. I had a similar experience with a failed rubber mount on my previous vehicle, although it wasn't a Mustang. Have you inspected the transmission mount and mounting bracket, to exclude any potential interference?

Thanks for your reply. I haven't specifically checked the transmission mount. Is there a straightforward way to visually inspect it for defects without disassembling everything?

While a visual inspection is possible, it can be challenging to diagnose mount issues definitively without proper tools or expertise. Given the electronic error and uneven idling you're experiencing, a defective cable or plug connection indeed sounds very likely. The symptoms point to a defective engine mount that, with the defective cable/plug connection, costs 95€. I would suggest going to a workshop to clarify the reason.

Thanks for confirming my suspicion and giving me the appropriate estimate for the repair. I took it to a workshop and, as you suggested, it was the engine mount with a defective cable connection. Got it repaired and all is well.