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Ok everyone. I ran into something this week that has me scratching my head. A buddy of mine recently purchased a 1994 Jeep ZJ with the 42RE, 4.0HO, Dana 35, and is 2WD. This vehicle is a Laredo, if it makes a difference. The vehicle has 250,000 miles on (what I presume to be) the original engine. It had plenty of power, and made all the right noises. Over the last couple of weeks, he's installed a cold air intake, a new set of wires and plugs, cap and rotor, freshened the CCV system, installed a new high flow cat and muffler, threw in a MSD coil I had, and installed my old ported and polished throttle body as well as a '99 WJ intake manifold. It ran very well after these mods and he was averaging about 16mpg in mixed driving. I then didnt see him or the Zed for a few weeks. This weekend, he came back with the CEL on, a weird, misfire at low RPM, a VERY low idle speed, and severe missing and what seemed almost like the fuel cut off on a very aggressive RPM limiter hitting right around 4000 rpm. His average MPG has also dropped to 15.2MPG and the truck feels noticeably more sluggish. We did the CEL sequence with the key and came back with a fault at the MAP sensor. I have a few new spares laying about, so we decided to throw them in. The issue persisted. Checked the vacuum line, all was in order. There appeared to be some fraying of the wires in the connector, so we checked them, made sure everything was plugged in and it all checked out. We checked plugs, wires, the coil, changed the fuel filter, tps, iac, cap and rotor, took down the exhaust before and after the cat.... issue is still present. I even have a spare ECM of the proper serial # ( I have a LOT of ZJ parts lol) that we threw in there and it's still displaying the same symptoms. The only thing that I can think of is that my buddy may have knocked a wire loose somewhere or perhaps accidentally created a short somewhere while installing a set of Hella fog lamps on his bumper. He ran the wires through the firewall grommet near the steering column into the passenger compartment, All vacuum lines and fittings seem to be in proper order, btw. Only other thing that I can think of is that maybe the CPS is failing, or we just need to swap out the whole ECM harness (I swear I have one somewhere in my closet). Any suggestions? I am honestly stumped. :dunno: