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Fuel injection flush?

Lately my 2004 Jeep Liberty has been lagging on acceleration and driving rough - my car barely responds to pressure on the gas pedal, and it kind of grumbles. This problem only occurs during the first few minutes of driving after I haven’t driven in a few days (I only drive once or twice a week). After the first few minutes, the car drives pretty smooth and normal. I took my car to a local shop, and they got a “misfire” code when they did the engine diagnostic. They recommended new spark plugs, battery service, and a “fuel injection power flush.” I got the new spark plugs and the battery service, but opted out of the fuel injection flush because I’ve read they’re really not necessary for most cars. Not to mention I got talked into getting a fuel injection flush only about 10 months ago. But here’s the thing - even after getting the new spark plugs, the problem persists. It’s not better at all. Do I really need to get the fuel injection flush? Will that solve my lagging acceleration problem? Or is there a different problem?

I was about to say try it, given your problems, until you said you got one 10 months ago. If so (and assuming it was a good one), another won’t solve your problem. It must be something else, so you need to get a good mechanic (not one that says to do a second flush in 10 months). Use the mechanic finder under actual car info.

I am going to guess that air is getting into the fuel system.

Many auto part stores will read engine error codes for FREE. You might want to get that done (again) and post back here what the exact code is, like [P1234] I would not consider another wallet … err fuel injection flush.

Went back to the mechanic, and he thinks it’s a faulty rear O2 sensor. The sensor isn’t communicating with the computer, hence the sluggish acceleration and rough idle when the engine is cold. This makes sense to me - any thoughts or experiences with this?
We’ll see when I pick it up later today…

An O2 sensor is not the cause of this problem (especially a rear O2) but may set a code due to another problem. An 02 is a pretty bad guess at the problem and I second Mr. Meehan about getting the codes read and posting them.