Idle air control and idle speed control

[joeCor]

The previous owner did an engine replacement. I was told my Idle air control was bad and to replace it but when I looked it up it is an idle speed control. Which from what I can see was not on my model and I only see it on wranglers. Wondering if maybe they swapped motors from a wrangler. My truck is a 87 base model

[eaglescout526]

It’s actually called an ISA or an idle speed actuator. They can be found on GM cars and yeah the YJ but not many places have it listed to fit the XJ and MJ due to the XJ and MJ getting the 4.0L more commonly than the YJ until 91. That being said, they rarely go bad and usually are misadjusted due to shade tree mechanics or techs who have never worked with or understand the Renix 2.5L to set it correctly. 
 

It’s possible for them to have swapped motors but that wouldn’t make a difference unless they swapped the engine management which they haven’t done at all and still has the Renix TBI. 
 

This all being said, is your engine behaving funny or have drivability issues?

[joeCor]

Yes it is idling very low and wills sometimes shut off if not givin any gas. It is also sputtering and bucking pretty bad especially in first and second gear. It is not all of the time though and I can’t make out any patterns on what makes it start happening. 

[eaglescout526]

Do you know any other history? Something like that with it having an issue while driving points me to a bad head gasket and not sensors if the head gasket has never been serviced and if it’s sat for a few years with coolant in it that would destroy the head gasket. I only say such cause mine checked out with all the sensors but the head gasket caused my problems with driving. 

The absolute only other thing that can give driving issues is the O2 sensor not being read properly by the ECU which is a result of bad/dirty pins in the connector on the harness side and would fault the system to remain in open loop vs closed loop.