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K. Wiggins
K. Wiggins, ASE Certified Technician
Category: Kia
Satisfied Customers: 3000
Experience:  ASE Certified Technician, Associates Degree in Automotive Technology, 15+ years in the trade
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Kia Rio: , I have a 2003 Kia Rio manual transmission with

Customer Question

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?
Submitted: 2 years ago.
Category: Kia
Expert:  Ron replied 2 years ago.
Hello, my name is ***** ***** I am a professional here at Just Answer. I have noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

The two lean codes your getting as well as the high fuel trims points towards an engine vacuum leak, and the common one on the Rio are any of the following,
  • Air Intake Boot
  • Intake Gasket
  • Purge Solenoid
    With the Purge solenoid being one of the common causes. To check this run the test steps in the link below.
  • Customer: replied 2 years ago.

    Hi Ron,

    As you see in my original question, I've already tested the purge solenoid and I've already checked for vacuum leaks....

    Expert:  Ron replied 2 years ago.
    Well if you have the fuel trim reading above 30% you a still dealing with a lean engine and In most cases its a vacuum leak. There really is nothing beside a leak that going to give you such high readings.
    Customer: replied 2 years ago.

    If you don't have any other ideas/thoughts can we open this back up for someone else to take a stab at it? I appreciate you responding but you haven't provided me with anything I haven't tried or knew already.

    Expert:  Ron replied 2 years ago.
    Sure thing, doing so rit now.
    Customer: replied 2 years ago.

    Ok thanks

    Expert:  K. Wiggins replied 2 years ago.
    Hello, another thing that needs to be checked is fuel pressure. It's possible the pressure regulator is dropping out at times causing the lean condition. I'll post the troubleshooting tree for both present codes at the link below. You've covered most of the items, but checking fuel pressure and the ECM connections is where I would suggest going next with it.
    ^ copy and paste link in your web browser to view.