real rough idle and exhaust leak

Yesterday my 92 cherokee started running rough. When i got home that evening and started it it would run but sound like 3 cyl. Got it home and put in new plugs, rotor and cap but no change. Then i noticed large crack in exhaust manifold. Can a cracked manifold make it run like its on 3 cyl. Checked fire on all 6 plug wires with timing like and it looked good. It doesn't have any computer codes showing any problem either. If anyone could help i sure would be thankful.

I've got a cracked exhaust manifold as well, makes the engine run a little loud but thats about all I've noticed. It's been like this for a long time for me, but I have never noticed any change in perfomace with my engine (4.0Lho). I'm eager to see though if there are any draw backs from having a cracked exhaust manifold. Just one more project that I need to get completed. Now where's that change jar.

Are U sure the hot exhaust didnt melt a vac line? Vac leak will make it run like poop. My 95 has had a cracked exhaust at the Y for years, when it gets hot the metal expands enough to quiet down like normal, Im just to lazy to R+R it. Might wanna check your EGR also.

Your 1992 id an HO engine- no EGR. Those ended in 1990, part of the Renix setup. Anyway, how old is the oxygen sensor? When mine ends its useful life, the result is a crappy running engine, sometimes with low idle. I'm on my third O2 sensor in 213,000 km/132,000 miles.