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Hello, I have a 2003 Kia Rio manual transmission with about 160k on it. When the car is first started in open loop, it run's a little rough at idle. If I give it gas, it will smooth out with no misses - runs good. When letting off the gas, sometimes the RPMs will stay up or even increase slightly from where I was reving the engine to. They eventually go down on their own, or if I put it in gear and creep forward a little they'll come down. Sometimes when the RPMs come back down closer to normal idle RPM it will then stall. Not always, but sometimes. But then I can start it right back up with no problem. It seems like once it makes it to closed loop, the stalling part seems to go away, but it still idles a little rough and sometimes the RPMs hang up. The RPMs hanging up sometimes happens while driving too - if I'm in gear accelerating and then go to neutral like coming to a stop sign, the RPMs will stat high like I mentioned above. While accelerating, the car has lot's of power and is smooth (no misses) and seems fine. But then at times, randomly while cruising or accelerating, the RPMs drop to nothing and all power is lost for about 1 second and then the RPMs jump back up and it drives fine. The car bucks when this happens from losing the power while moving. This can happen back to back or just every once in a while. I have 2 codes, P0171 and P1166. Monitoring the data, obviously, there is a very high short & long term fuel trim - in the 30s, I think 33. The front o2 sensor voltage is extremely lean (just above zero). Using propane in the intake, the o2 sensor voltage remained extremely low so we replaced the o2 sensor but this had no effect on what we experience with the car. We also used the propane around the vacuum hoses and intake and weren't able to identify any vacuum leaks. We unplugged the MAF while it was running and saw no change in the idle so we swapped with a known good MAF - still no change. TPS tests ok electrically. Purge valve has no leaks and opens with 12V applied and closes normally once voltage is removed. IAC seems ok and the ECT seems ok too. Plugs (NGK) looked ok and we sprayed the plug wires with a mist of water while running and no arching seen. We looked at timing and it appears to be in order as well. There doesn't appear to be any mechanical failures with the engine, as I mentioned the power is really good when accelerating but at times, it cuts out. Any thoughts?
Why did this get moved to transmissions? This is not a transmission concern.....