FiveAngels

Guy,

My 2001 GC limited (4.7 V8 at 140,000 miles with Auto Transmission) started having very bad gas mileage from the last 2 weeks and idle problem when engine already warmed up. Prior to this bad mileage problem, it was acceptable because this car is 10 years old.

Currently, everything seems to be fine with no engine light.

What I have read from this forum so far, the 4-O2 sensors and MAP sensor might be a good place to start with for the fuel economy for my 2001 GC.

The problem is when I am not sure which I should try to replace first. Should I replace all 4 of O2 sensors at once? Or, I can replace them one by one in the range of 6 months or a year.

For the MAP sensors, is it necessary to replace it before I replace O2 sensors, or, should I replace them all at once, MAP and O2 sensors?

And, the other problem is I do not know exactly where they are. I have seen many diagrams from this forum, showing the sensors. However, with the untrained eyes, it does not look familiar to me when I actually look under my GC 2001 hood. Can someone help locate 4-O2 and MAP sensors of 2001 GC 4.7 V8, please?

For the idle problem, after then engine is warmed up, the idle will come down to 450-500 rpm. Once in awhile the idle would go back up to 650-750 rpm for the range of 10-30 minutes and go back down to 450-500 rpm gain.

Some of the posts from this forum suggests that O2 sensors can contribute to this problem. AutoZone suggests that I need to check for leaking vacuum. Where should I start with for this problem. I hesitate to take it to the shop without a knowledge of possible problems.

TIA

captainwoot

If you have no "engine light" this means that your sensors are operating correctly. And yes looking for a vac leak is a good idea, usually a leak will give you a higher idle ( and this will also turn on the engine lamp) I think you best bet is to locate the ais )idle speed motor on the throttlebody, remove this and clean it as well as the throttlbody itself. How are your spark plugs and airfilter? check these first for mileage concerns.

captainwoot

Sorry #3 is you idle air control
Good luck!

FiveAngels

Thanks for you suggestions, Captainwoot.

For the AIS motor, are you referring to IDLE AIR CONTROL MOTOR (IAC motor)? If it is, I will clean it and report back at later time. For the throttle body, can I just clean it with clean cloth?

I did the tuned up last year at the local mechanic. He only replaced the spark plugs and air filter. I was wondering if the dealer would do further clean/checkup at the tune up time.

What I will do first is to get my GC tuned up at the Jeep dealer, clean the IAC motor, and use fuel injection cleaner (Seafoam?). If these do not help, I might replace the O2 sensors as the last option.

At 140,000 miles, would Seafoam help my GC engine? I have never once use motor treatment or fuel injection cleaner on my GC. I was told that they would do harm than good. But, from my reading in here, I was convince otherwise.

Do you any suggestions of what fuel injection cleaners or engine treatments that would benefit my GC at this point?

TIA