Got a problem here. So the jeep has been running rough recently and my gas mileage has tanked. I used to get like 20 on the highway and now I get like 12 to 13 max. It doesnt have a loss of power but just horrible mileage and rough idling. Also, the idle is low like 400 to 500. I believe the cherokee is supposed to be at like 700 to 900 correct? I have read up and found it could be the map sensor. I thought about the tps but it shifts smooth as butter so that couldnt be it (?) Also, maybe the cps. There are too many sensors to deal with. If anyone could help me that would be great. Oh and its a 2000 I6 4x4 with 135000. Thanks!

 

When's the last time any preventive maintenance was performed? Such as...

Spark plugs replacement,

Oxygen Sensors replacement.

Do you have acess to a Scanner that can display live data when the engine is running? If so, look for Short Term Fuel Trim data. And, before starting the engine (after it sits over night), check the IAT temp vs. ECT temperatures to see if there's in excess of 6* F difference between the two. Engine Coolant Temperature sensor has a big influence over fuel management. The MAP sensor is the No.1 contributor to fuel management.

Before shotgunning any sensors, remove the spack plugs and check their condition. See what deposits are on them, check the gaps (.035" max), and what plugs are being used. NGK ZFR5N plugs are the factory recommended plugs.

 

Spark plugs are ngk and gapped correctly. They are about 8000 miles old. Oxygen sensors are ngk and pretty new. I noticed yesterday while sitting in traffic I started to get a little warm like 215 220 F and the idle rose to 600 rpms and it ran better.

 

Try a new Engine Coolant Temperture sensor.

Remove Inlet Air Temperature sensor and clean the probe with Mass Air Flow Sensor Cleaner (only). Do not disturb the temp probe in the cage.

 

Gonna pick one up today and go from there.

 

Hook a scanner to it and check throttle position at idle. It should be at zero, if it's higher, clean your throttlebody.

 

Throttle body is clean as a whistle

 

put the new temp sensor in. The idle didnt change much, still holding at 500 rpms. well see if the idle smooths out and my mileage changes. If this doesnt work what would be my next step?

 

"I noticed yesterday while sitting in traffic I started to get a little warm like 215 220 F and the idle rose to 600 rpms and it ran better."

Does this situation still exist? This is why I thought a new ECT sensor may help.

How does the inside of your valve cover look (viewed through the oil filler hole)? Is it kind of cruddy? If your CCV fitting orifice gets plugged up it will cause a low RPM.

How does your tailpipe look? Do you see black soot around the inside (like it has been running rich) or do you see a light brown deposit. Is there water dripping out the tail pipe when first starting up, and then it goes away, or if it's drippng, does it stay dripping even after the engine warms up.

I can show you how to check your MAP sensor if you think that's what you want to do. If so, round up two safety pins for back probing and a digital voltmeter.

 

The ccv lines are brand new just redid them last year. The tailpipe is very sooty and yes water comes out at start up and continues as it runs

 

Pull your spark plugs and see what kind of deposits are on them. If there is any sooty deposits on them it would indicate that cylinder is runnng rich.

What exhaust system do you have, the California emission exhaust or the federal exhaust.

California emissions exhaust:

 

I got the cali emissions. And okay ill pull the plug this weekend

 

So i checked the map sensor, voltage is good on it. Also, i revved the engine to like 4 grand to try and clean some deposits out of it and i noticed a puddle by the exhaust, like a good amount of water came out. dont know what that means??? my next step is going to be spark plugs and probably the cps sensor

 

Is it possible that 'water' is engne coolant? Are you losing coolant?

Don't just change spark plugs, ull them and inspect them. Take a good closeup pic of them and post it up if you can.

I don't think it's a CPS at this time.

 

Water coming out of exhaust is common on startup, happens in most vehicles.