Hey, sounds like you're having a tough time. I've got a 2000 Toyota Celica and encountered a similar issue a year back. Although I'm not a car guru, just a guy with some decent experience under the hood, it really sounds like a defective lambda sensor heater to me. I took mine to my trusted workshop, and they confirmed my lambda sensor heater was on the fritz. The repair set me back about 375 Euro but it sure felt worth it. The poor performance, black smoke, and that pesky check engine light are all gone now. I'd strongly recommend you do the same. Now, could you share your model's specifics? Like the size and type of the engine, is it turbocharged, the mileage, etc. It might help us figure out if you've got the same issue as I did or not. All the best!

Hey there, thanks for the advice, really appreciate it. To give you a bit more detail, my Supra runs on a gasoline engine, it's not turbocharged. The odometer's reading around 147,851KM currently. Last time I took her for a service was around the 145,000KM mark, so I suppose it's due for another one soon. The mileage plunge is really bothering me, hope it's just the lambda sensor acting up. Gonna take her to my mechanic soon, fingers crossed. Cheers!

Hey there, your details point quite clearly towards a similar situation I had. Your Supra and my Celica are both from the Toyota family, gasoline engines and around similar mileage when I noticed the problems. The lambda sensor heater malfunction sounds more plausible now. I'd definitely recommend taking her in for a check-up and tell your mechanic about your suspicion. This kind of issue tends to affect the car's mixture control causing your fuel economy to reduce dramatically and that black smoke from the exhaust is another sign. My Celica's performance improved tremendously after getting the defective lambda sensor heater fixed up. Maybe an early service wouldn't hurt, it sure did save me from a lot of headaches later on. Best of luck champ!

Ah, that's comforting to hear! It's always a relief to connect with someone who's experienced a similar issue with their car. Armed with your suggestions, I'm definitely feeling more prepared about taking her down to my mechanic now. An early service does sound like the best next step - better safe than sorry, right?! I'll keep you posted on what the mechanic says. Thanks for your help!