Toyota iQ Automatic Transmission Issue

I had a similar issue with my old Renault Clio, though it was a manual. Intermittent starting problems, check engine light... Drove me nuts! The problem was a faulty sensor on the transmission itself. The car didn't know which gear it was in, so it wouldn't allow the engine to start sometimes, especially in neutral. Did you check the transmission sensors? Maybe one of them is sending faulty data to the control unit, causing all the problems you described.

Thanks for the tip! Which sensor was it exactly on your Clio? And where is it located on the transmission? I've looked at some diagrams, but I'm not sure which one would be related to the parking position. Is it difficult to replace? Any special tools required?

Unfortunately, I can't recall the exact sensor on the Clio. It was a while ago, and the workshop sorted it out. From your description and the error codes, it indeed sounds like a faulty transmission sensor or the control unit itself. Given the symptoms and potential cost of messing around with the automatic transmission, I would recommend taking it to a trusted workshop. They have the tools and expertise to properly diagnose and fix the problem.

Turns out you were right, it was the transmission control unit! The workshop confirmed it was defective, like we suspected. They replaced it, and now the car runs like new. Cost me about 1000€, which stings, but at least it's fixed. Thanks for pointing me in the right direction. Your experience with the Clio helped a lot!