2012 Scion TC
I had a friend that took my car out without permission and ended up moneyshfiting he was going 60 and put it into 1st gear he saved it a little by pressing the clutch back in and not letting it fully into gear but still ended up messing something up, the car still drove and it seemed like nothing was wrong, the car now has a misfire that happens through lower rpms and higher rpms it clears up when your on it around 4 and a half k and then if you keep going into higher rpms now it will flash the Check engine light at you and you will only have enough power to keep you rolling until you let off the Gas for about 20 seconds then the car will drive again. There's no oil leaks my car would naturally burn oil before this with no problems with the car and it hasn't seemed to pickup at all, my gas milage is now 18mpg but I do drive semi fast. I replaced spark plugs and coils, it would go back to normal until the Check engine would flash at you and then would be back to misfiring. I got it coded before and it popped up misfire on cylinder 2 and 4 and multiple cylinder misfires. The car still runs 2 to 3 months later if you let it sit and idle for awhile it will get a loud ticking sound and once you drive it it goes away.
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Your friend seriously over revved your engine by downshifting like that.
By your symptoms, it's time to do a cylinder leak down test on cylinders 2 & 4.
Downshift over revving can damage the valve train causing an intake or exhaust valve to not completely close.
When you put air to the cylinder (TDC, compression stroke) during the leak down test, you can also listen for air escaping from 4 places. The oil fill, radiator fill, throttle body (open the throttle plate), and exhaust pipe.
In your case, listen carefully at the throttle body and exhaust pipe if you're losing air pressure too quickly.
You'll find plenty of youtubes on how to perform the test and interpret the results.
