88 Cherokee running rich, burning gas, lurching

[Gavman]

RE: Vent stuck in defrost position

88 Limited 4.0 auto. Looking for help to start diagnostic. Not sure if it's timing, sensors, vacuum, fuel line or what. Thinking of paying someone to put it on the computer. I'm getting 10-12 mpg, and blowing black smoke. Also, when at stop light, and foot on pedal it starts lurching and the idle goes from 300-800 rpm and back alternatingly repeatedly. Additionally, when decellerating from about 40mph down to below 30mph it doesn't feel smooth, and then it shutters violently until I give it a little gas. Any and all suggestions will be greatly appreciated. Thanks.

 

[dingus]

black smoke means you're running rich. my guess would be a sensor or vacuum leak... is your check engine light on? how many miles are on it? how current are you with maintenence?

 

[Gavman]

gotta love the marines...

I don't know the maintenance history as I recently purchased it. It has 220k miles. Check engine light is not on. I did have to unplug and replug the crankshaft position sensor once when it wouldn't start. Could a bad cps cause these symptoms? It's a good place to start as I know there have been problems with it. I'll check vacuum lines as well. Thanks for the response.

 

[dingus]

RE: Thud

i sent u a PM with a link to download a copy of the manual for your jeep. i would suggest testing all of your main sensors, it should give you a target amperage/voltage/wattage/whatever you're looking for so you can make sure everything is telling your computer the correct information.

i'd also replace your spark plugs as a simple and cheap way to make her a little smoother. if you're running rich, part of it may be because your plugs are fouling.

ps. good to find another high miles buddy (217k here)