For the average DIYer, you don’t need to go crazy expensive, but you do want something that can read more than just basic codes. If you’re just getting started A simple Bluetooth scanner like BlueDriver or an OBDLink with an app is honestly hard to beat. Cheap, easy, and gives you live data which is where real diagnostics start.

@Victor Hutchinson I would go with a lunch x431 then

Hey @Ovidiu Rotar 👋🏼

Hey Ivan! There’s actually a lot of useful information in what you posted, so I’d definitely stop replacing parts for now and work through it systematically. The biggest thing that stands out is that you said the car seems fine when it’s cold, but once it reaches normal operating temperature the RPM starts dropping and it wants to stall. Combined with the previous P0171/P0172 codes, I’d want to focus first on what the engine is doing with fuel control once it’s warmed up rather than assuming it’s piston rings or a failing transmission. A few things would help us narrow this down… 1. Is this the 2.5L non-turbo engine? 2. Which O2 sensor is disconnected right now …the front/upstream A/F sensor or the rear/downstream O2 sensor? 3. When the catalytic converter was removed, was it completely hollowed out/deleted, and was anything changed or tuned in the ECU afterward? 4. Do you have access to a scan tool that can show live data? If so, we’d really like to see your short-term and long-term fuel trims at fully warmed-up idle and again around 2,500 RPM, along with the A/F or O2 sensor readings. 5. When it starts trying to stall at a stop, if you shift it into Neutral or Park, does the RPM immediately recover? 6. When you say it “loses oil around 3,000 miles,” how much oil are you actually having to add over those 3,000 miles? Are you seeing any visible oil leaks or smoke from the exhaust? The oil usage may be something worth looking into, but we wouldn’t jump straight to piston rings based on that alone. If it’s only slightly low around the time you’re due for an oil change, that’s very different from adding multiple quarts between changes. The O2 sensor situation is especially important here. If the front A/F sensor is the one that’s disconnected, that needs to be addressed first because the ECM relies heavily on that sensor for fuel control. The fact that your fuel consumption jumped to roughly 15–20L/100km also tells me the fueling needs to be looked at closely.