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Old 01-15-2015, 09:29 PM
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low rpms at stops and bad gas mileage

2004 JGC 4.7
experience low rpms at stop lights ...400 range with stalling issues as well at stop at times. Gas mileage went from 15 to 11 mpg per fill ups.

New battery in November. No codes have registered. I cleaned the throttle body. Replaced the TPS and the IAC. Took it to a dealership and they ran diagnostics testing and it passed with a clean bill of health...everything checked out OK. They do not know what the problem is.

Does anyone have any ideas on this?

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Old 01-16-2015, 11:14 AM
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Re: low rpms at stops and bad gas mileage

Any smell of raw unburnt gasoline from the exhaust? Can be that O2 sensors are not working well, making the mixture too rich. If this is the case, then it has to be repaired ASAP, because it can damage the catalitic converter. Put the jeep on a scanner which shows live data and check the voltages of the 1-1 and 2-1 sensors. They should change rapidly from 0.2-0.8 V. If one of them is steady, then its probably time for new O2 sensors.
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Old 04-09-2015, 11:23 AM
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Re: low rpms at stops and bad gas mileage

Update per my low rpm problem at stops....sorry for the delay. I followed Franks direction with the o2 sensors, as that was in the back of my mind, even after the dealer diagnostic testing showed nothing wrong with the Jeep.

Now it turns out our Jeep with a single exhaust, has (4) o2 sensors instead of 2. The reason is it is a California emissions Jeep, sold new in PA, with no info on the window sticker or anywhere else. I was under the impression that this info was to be noted as such. At any rate, along with a new oil change it does run much smoother. It does still fall in rpms at stops, although not nearly as often and overall runs better and smoother.

Thanks Frank.
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Old 04-09-2015, 11:51 AM
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Re: low rpms at stops and bad gas mileage

The two upstream sensors (1-1 and 2-1) are the ones which are used for the fuel mixture regulation. The two downstream sensors( 1-2 and 2-2) are used for monitoring the efficiency of the catalitic converters.
To know if the rpm dip problem is engine related, or maybe torque converter, you could put the transmission in N just before coming to a stop. If the rpm still dips, then the problem should be engine related, but if it doesn´t, then it could be a problem with the torque converter (sticking torque converter clutch for example)
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