No power, cannot go over 50 mph, idles rough

  • 2001 KIA SEPHIA
  • 1.8L
  • 4 CYL
  • 2WD
  • 150,000 MILES
Car gets up to around 40 mph just fine but then it goes to heck. Getting to 50 mph is a job. Down hill on the highway the car will slowly gain speed to cruise at 75 mph on down grades and flat lands but the minute any kind of incline is attempted the car falls flat on its face, rapidly going down to 3000 rpm and 35-40 mph for your uphill speed. The codes that popped were for a mis on cylinder 2 and mass air flow output voltage low. Unplugging the mass sensor did change my speeds by a little, letting me go faster on my uphill climb but only by a couple mph. I am also hearing a loud hiss sound on acceleration, almost like a turbo whine, I realize this is probably a vac leak that I need to track down. Thought I would ask for ideas before throwing money at parts. Thanks in advance.
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have the same problem?
Friday, June 14th, 2019 AT 9:51 PM

1 Reply

Welcome to 2CarPros.

If you hear the noise on acceleration, it sounds like a catalytic converter is plugged. A misfire can lead to damaging the converter by dumping raw fuel into the system. When you accelerate, the vacuum in the engine drops so that wouldn't be when you hear a leak.

Take a look through these links. They explain how the converter works and how to check them. Basically, you need to remove the o2 sensor so there is a place for pressure to exit.

Try that and let me know the results.

Take care,
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Friday, June 14th, 2019 AT 10:15 PM

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