Chosen Solution

I have not for the life of me been able to find an answer or a fix for this problem that seems to be a known issue with these models. I am assuming its the type of glue or plastic that they used when manufacturing the laptop because it smells like a cheap plastic outdoor chair that has been sitting in the hot sun. If anyone has any recommendations on how to fix the problem, even if it comes down to replacing a whole part, then I’m totally down! it’s so embarrassing.

Hello Gwen, Is there any news on this topic? I am experiencing similiar issues with my mid 2012 macbook pro - MD104LL/A On top of this issue, my MacBook Pro runs really hot. I created a clean user and it runs about 70°C to 80°C in idle – and I think both problems connect to each other. So I couldn’t solve it right now, but might have identified the source of bad smell in my case. I have to say, I already replaced the old thermal paste and my system is cleaned. Sadly this didn’t give the results I was expecting, as temperatures kept beeing hot. But, I figured out the bad smell might come from the keyboard itself. In the macbook the CPU and GPU heatpipes run under the bottom of the keyboard with little to no space left. So the bottom of the keypad plastic and electronics is getting really hot as well. I didn’t take any pictures, but please check out this fine youtube video. There you can see clear marks left from the heatpipes to the black bottom plastic of the keypad. 2012 Macbook Pro 15" A1286 CPU Heat Sink Replacement I think this is the source of bad smell. Also in my system, the little silver-colored-patch in the bottom left corner below the logic board is peeling of. My system has a really bad battery too. So I’m swapping the battery. Maybe it solves the temperature as well. In the next step I will swap the heatpipes and swap the fans as well. Hopefully this will achieve full cooling again to the MacBook Pro. Update (08/17/2020) I’ve fixed the smelling issue with my one. Rather than the plastic that is off-gassing it is the thermal pads below and on top of the memory slots.
They have gone bad and were pretty brittle I’ve removed them and that removed the bad smell as well.

Sounds like you have something burning inside. Have you opened the system yet? I would start there looking for plastic parts that appear melted. Also look at the components not just on the visible side you’ll really need to take the logic board out. You might as well clean the old thermal paste off and apply a fresh coat. Follow this guide MacBook Pro 15" Unibody Mid 2012 Logic Board Replacement