Curious low idle question

[88eliminator]

Hello everyone, 

 

I have a 1988 Jeep Comanche Eliminator, 2wd, 4.0 aw4 trans with about 86,000 miles on it. 

 

My truck will start every time and idle great at 800 /750 rpm when its cold but it fluctuates a little bit. With the AC turned off and the truck is at operating temperature the truck will idle at 500 rpm or lower at times and fluctuates a lot more. The truck drives completely normal until you come up to a stop light and the idle drops and acts like its going to stall but goes right back up to 500 rpm. When the idle is at 500 rpm It hesitates very little right when you take off but other than that it drives fine. The truck will not stall at all but it feels like it going to but it doesn't.  

 

This is when I am very curious. With the AC turned on and the truck is at operating temperature the truck will idle perfect at 750 rpm and will only occasionally fluctuate.

 

I am just wondering what could cause the idle to be fine with the AC on and the idle to be low when the AC is off. 

 

Note: This low idle has just started happening right after I changed the fuel pump other than that it idle fine before the new pump. the idle has always fluctuated when I first got the truck but hasn't been a problem.

 

What I have Changed so far:

• New Plugs/ wires
• New distributor cap/ rotor
• New coil
• IAC
• TPS
• CPS
• MAP censor
• New vacuum harness
• New fuel pump/ filter  

Any help will be great. 

 

Thanks.

 

 

 

[Crash]

Confirm your e-fan turns on with the A/C. IF it does, then most every vehicle bumps up the engine rpm while the A/C is running.

Not all parts created equal, consider the possibility that your IAC could be bad/not adjusted properly.

[cruiser54]

Make sure your intake manifold bolts are snug.

 

Clean your throttle body and IAC. Tip 11.

 

Click on the link in my signature and do Tips 1,3,4, and 5. 

[88eliminator]

Confirm your e-fan turns on with the A/C. IF it does, then most every vehicle bumps up the engine rpm while the A/C is running.

Not all parts created equal, consider the possibility that your IAC could be bad/not adjusted properly.

Yes my e-fan does turn on while the A/C is on. 

 

Thanks for your advise and I will make sure to double check my IAC. 

[88eliminator]

Make sure your intake manifold bolts are snug.

 

Clean your throttle body and IAC. Tip 11.

 

Click on the link in my signature and do Tips 1,3,4, and 5. 

I just checked my manifold bolts a couple days ago.

 

My next thing to do is to clean the throttle body and the IAC.

 

Thanks again for your advise.

[cruiser54]

 

Make sure your intake manifold bolts are snug.

 

Clean your throttle body and IAC. Tip 11.

 

Click on the link in my signature and do Tips 1,3,4, and 5. 

I just checked my manifold bolts a couple days ago.

 

My next thing to do is to clean the throttle body and the IAC.

 

Thanks again for your advise.

 

Do the Tips.....