MR2 heater blows cold air

Interesting! I had a similar problem with my old 2008 Saab 9-3. My heating was also weak, and it turned out to be a partially blocked valve somewhere in the cooling system. Apparently, it's not uncommon for gunk to build up over time and restrict the flow of coolant to the heater core. Have you checked your engine coolant level recently? Is it nice and clean, or does it look a bit murky?

Thanks for the tip! The coolant level seems okay, but I haven't really looked closely at the coolant itself. Where exactly is this valve located? And how would I go about cleaning it? I'm pretty handy, but I don't want to mess anything up.

Okay, so on my Saab, the valve was near the firewall, where the heater hoses enter the cabin. However, your MR2 is a different beast altogether. I wouldn't recommend trying to clean it yourself unless you're really confident and have a service manual handy. You could easily damage something or introduce air into the system. Honestly, for the sake of peace of mind, it might be worth having your mechanic take a closer look. At least they can properly diagnose the problem and give you a firm quote.

You were spot on! Took it to the mechanic, and it was a defective water valve, just like he suspected. Turns out the cable connection was indeed faulty. They replaced the valve, and now I've got heat again! The whole thing cost me 95€.