Hesitation, rich mixture, rough idle.

1999 MITSUBISHI ECLIPSE
165,000 MILES • 2.0L • 4 CYL • 2WD • MANUAL
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REYNALDO SOTO
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I have been troubleshooting my car for a couple of weeks now and cannot seem to figure out what is wrong. i went from getting close to thirty mpg to now almost ten. When i accelerate the rpm's go up, but the car does not go any faster. it does not happen in the morning or when i first start the car, but later in the day or on a long drive it happens and gets worse. i lab scoped multiple sensors and they all came out to spec and gaped the spark plugs to spec. Also hooked up a four gas analyzer and my hydrocarbons are over 350. Vacuum pressure, fuel pressure, back pressure, and compression are excellent. I honestly do not know what else to do and some other perspectives would help greatly.

Reynaldo
Apr 11, 2018 at 11:29 PM
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MHPAUTOS
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Have you checked the voltages at the O2 sensor?
Apr 12, 2018 at 7:03 AM
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REYNALDO SOTO
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I am doing it right now.
Apr 12, 2018 at 10:48 AM
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REYNALDO SOTO
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Just lab scoped both O2s and they are almost perfect. also voltage is up to spec.
Apr 12, 2018 at 11:15 AM
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MHPAUTOS
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You will have to get in with a live date scope and start checking all readings, you seem to have a good grasp on what is going on, but do not forget all the basics and do not presume something is okay. check and double check, check base timing and timing advance, fuel trim, get your specs sorted and go check the system out from end to end.
Apr 13, 2018 at 12:53 AM
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REYNALDO SOTO
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Will do, thanks for the help.
Apr 13, 2018 at 9:09 AM
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STEVE W.
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Do not forget to test the sensors when the issue is happening. It sounds like the heat of a warm engine is changing the operation, heat sensitive issues can be a bear to find. One thing I do is get the engine into the "bad" area of operation, then cool down electronic modules under the hood one at a time. The cheap way to do that is to use the "canned air" sold in stores to blow off dust. Turn the can upside down and the actual 134A used in them comes out. Wear gloves and eye protection, it can freeze human tissue on contact!
You can also do that while testing a component.

You also mentioned that when you accelerate the rpm's rise but you do not gain speed? I would check the clutch, it might be worn enough that it slips enough to cause problems. Another thing would be to use an IR thermometer to check for brake drag. A bad brake line could cause a slow rise in brake pressure and cause drag. Depending on the brake materials the heat may not be bad enough to cause typical brake smell.
Apr 13, 2018 at 4:20 PM