I would defiantly change the transistor mate as mine did this when I had it and that's what it was. I bought the car from my father in law and they just drove about in it for a year with it intermittently coming on. I fixed it in the first week I had it and never had a problem with it after. I was a good car.
I would remove the imrc box and take it into an electronics repair shop they will change it within 10 mins for not a lot of cash.