I am new to Jeep again and as I have mentioned it is a 1989 Cherokee with a 4.0L and auto. Now it runs great but my problem if you can call it that is that my engine only idles at about 300-400 RPM, and the altenator has trouble keeping things charged at idle.

What is the normal idle speed? What could be causing this or can I do to remedy this?

What is a cheap and quality lift I can put on the Jeep to put on 31" tires? Though that is not as important.

 

That is pretty low, does it idle very smoothly or is it jerky/rough?

 

It idles smoothly it is just really low. There is barely any fast idle as it idles around 500-600 RPM when cold but once it warms up it drops down to 300-400 RPM.

I am putting a little bit of work into it.

So far have done a complete tune up cap, rotor, plugs, wires, filter, oil and filter and replaced the negative battery cable. Not sure what is causing this strange idle issue though.

 

Something else I plan to replace is the thermostat. I think stock is supposed to be 195 and my jeep doesn't get above 170 degrees. Is that something that could make a difference?

 

a thermostat wont make a difference in idle, but it will get you alot better gas milage. you have an adjustable idle, there is you TPS (Throttle Position Sensor), it is located in front of your throttle body and is ID'd by having 2 screws on the front of the sensor and being on the right front side. if you look behind it, it has a little finger that goes up and down as you add or decrease the throttle, you can looses the two screws and turn it slightly to the right to add more idle and to the left for less. i belive it is suposed to be at 11-13% efficiency, but you can only check that with a scanner. otherwise just adjust it with the jeep off, and then turn it on, check the idle (at operating temp of 195* or higher, so change the thermostat first) and you will be on your way.

 

Idle with a hot engine and trans in D is 750 RPM...

 

ive been chasing the same problem, ended up putting a tiny wedge between the little thottle am and the stopper, runs gret now

 

Thanks guys will do. You know I was about to try to adjust the throttle the same way as described and then I noticed the plate that said idle was non-adjustable. Of course I really didn't want to be out there messing with it in the middle of the night in Northern Ohio weather.

 

Thank you I thought that should be about what it is. I knew with it ideling around 300 RPM that was not right, but atleast I know it is running well enough to idle at that RPM.