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Mitsubishi Eclipse misses and revs high

Hello all,

A few weeks ago my '03 Mitsubishi Eclipse missed for the first time since I’ve had it. It’s a 4-banger, so it was definitely noticeable. Fast forward a couple weeks and after a trip to Texas (from Tennessee), it begins to run between 2,000 and 3,000 RPM on start-up. There is a lack of power (not attributed to the small engine size) that was not present until a short time ago. It stopped doing that, and today a service engine light came on. The code was P0134. Some things about the car- the oil is changed religiously every 3-4 thousand miles, and the only major repairs were several years ago- the clutch and head gasket. Spark plugs are 2 years old, and coil packs were checked out around then as well.

Any help would be much appreciated.

According to what I have here P0134 means there’s no activity on your O2 sensor Bank1, Sensor 1.
That’s the one prior to your catalytic converter and that is used to adjust the engine’s fuel/air mixture, etc. You may want to check the wire going to it - maybe the thing has a bad connector.
If not, that’s usually a heated sensor and sometimes the heating element opens up, requiring it to be replaced.

Is that something where once it goes, it’s gone? The reason I ask is because the service engine light went off about five minutes ago on a short drive across campus.

The O2 sensor has probably become lazy. The O2 sensor produces it’s own voltage signal from 0-1 VDC depending on the oxygen content of the exhaust gasses. These are called cross-counts. If the O2 sensor flat-lines or no longer produces those cross-counts the Check Engine light comes on and you get that code. Take the vehicle for a cruise on the freeway to see if Check Engine light comes on again. If it does with the same code, O2 sensor has become lazy and requires replacement.


Awesome. Thanks so much for the advice. That’s twice you’ve come through on the Eclipse. Do appreciate it!

A quick clarification- You are referring to the upstream 02 sensor?

This one?

Good idea to change both the upstream and downstream sensors at the same time. Not doing so may confuse the computer. If you see them you can do tt your self. Be sure to use the special socket. buy or rent at Auto Zone.