My car will not exceed 2500 RPM in any gear

Why would you or anyone assume fuel filter is original? Last owner may have done all required services.

P0128 is likely a stuck, incorrect or missing thermostat.

The P0121 is a one trip DTC that puts the computer into limp mode. It must be addressed first. Remove the plug from the TPS (throttle position sensor) located on the throttle body and use a multimeter to measure the resistance between the center pin and either outer pin. while the meter leads are in contact with the pins, have someone step on the gas pedal slowly and the resistance should change smoothly. Check for this on from the center pin to each of the outer pins. Odds are that you need a new TPS.

I reset the codes and the problem disappeared instantly and completely. The fault originally happened when I jumped the engine after I was done coasting down a very long hill. I presume this caused a transient error code that set the computer into a safe mode that someone mentioned in earlier messages. At this point, I will watch for fault lights and cross my fingers.

Stoveguy - Well perhaps I assume this because the car was missing every one of the nuts and bolts holding on the largely cosmetic engine cover and the air filter. A shattered electrical connector was ā€œrepairedā€ with electrical tape causing two cylinders to not fire whenever it fell partially out. The car simply did not look like it had been serviced competently by the previous owner. It usually runs fine and I got it for a relative song so Iā€™m not complaining. But Iā€™d be a fool to think I can count on a perfect servicing history. Which reminds me I should change the timing belt sooner rather than later.

Did you ever figure out why your Kia Rio wouldnā€™t exceed 2500rpm in any gear? Iā€™m having a similar problem. Thx.

Did you ever figure out why your Kia Rio wouldnā€™t exceed 2500rpm in any gear? Iā€™m having a similar problem. Thx.

Hi. I know this post is a bit old but just wondering, could you manage to find and fix the issue? If yes, what was it? I own a Kia Rio 1.1 diesel with the exact same problem.

His was a gasoline engine, so what ever his problem was isnā€™t going to help you.

That, plus the fact that Kia Rio diesels are not sold in The US, where 99% of this forumā€™s members resideā€¦