I recently purchased a 90 jeep cherokee laredo with a 4.0L motor. Well i was having a problem with it overheating, so i replaced the jug and fixed that problem. well ever since i got it i have never drove being that i have only owned it for about a month. well today i went to mess around with it to see if i could fix the idle problem. In park it revs about 2500 to 3000 rpm but as soon as you put it in gear it jobs down to about 800 to 1000 rpm but when i took it down the street it had no power it was like spitting and sputtering wouldn't rev over 1500, kinda seemed like when ever i gave it gas acted like it was running out of gas, and i know that it has gas being that i just put 5 gallons in it. any suggested ways of to start trouble shooting this problem? cheap ways are the best being i just got layed off work too

 

Check and see if you have water in the oil or oil in the water, pull the plugs, run a compression check on the engine.

 

checked the water oil situation and water is clean and oil is clean both ways

 

Sounds like something with the timing. Take it to you local big chain auto parts place they may put a timing light on it for you. Also check the bolt which holds your distributor in place for wrench marks and to see if it is tight, the PO may have messed with the timing in order to remedy another problem.

I do not know a lot about jeeps since i just bought my first one a month ago but, if it yours is fuel injected it should have a throttle positioning sensor which may need adjusted or replaced.

Another possibility, though slight, is a blown head gasket or some other form of loss of compression.