I have a 2001 jeep grand cherokee 4.0l automatic
Ok about 3 month ago the idle started acting up was either to fast or slow,
So I replaced the iac and it was ok for about a month then one day it would only start if you gave it a little gas,drove it home and now it idles at 12-1500
So I replaced the iac 2 more times thinkg autozone gave me a bad part,still idle is too fast so a friend of mine has a drb3 scan tool we hooked into the ecm and can change idle up from 1200 to whatever I want but not down from 1200 scan tool shows the ecm has commanded a 0 step which is closed on the iac and if you plug the iac hole it will idle down this eliminated any vaccum leaks,so I ordered a new iac from napa (they have better parts imo)
Put in the iac today and idle came down to 700-800 and I could here a little miss in engine then rpm went up to 1000+ so I pulled the plugs out they had 50-80k on them anyway put in new plugs with the same issue start it idles ok for a sec then misses a little and rpm go up,I tested tps with a vom seemed ok,any body have any clues as to why it would miss at idle the ecm raises rpm to clear miss,I have 140k on the jeep never had any problems other than cooling fan replaced 6 month ago and did water pump just because It was easy to get to after ripping front end off to replace cooling fan.
Thanks for all the help next step I guess will be a dealer