I have a 1997 Jeep Cherokee 4.0L. I just got my jeep fixed when I had problem with my jeep not starting unless the acceleration was down, and even when on it would die if i was not pressing the gas. I finally got that fixed after(took 2 months to finally find the reason,mechanics didnt help at all) getting a tuneup, replacing the Idle Air control, Throttle body sensor, Battery, and Battery cables. But now my jeep is starting up with a loud clanking/rattling sound. And when in idle will randomly drop RPM's and make the loud clanking/rattling sound. Kinda sounds like something is loose.

Well, it could be the problem that I have with my '97. The exhaust downpipe crosses over the trans-support crossmember. There is very little clearance and the downpipe has a "finger" that fits into an exhaust bracket. On mine, the "finger" rusted off. I initially thought it was old motor/trans mounts and replaced them before finding out that this is a common problem. Shop said that they could weld a new "finger" on b/c the pipe is a mild stainless. Getting that done next week.

Just like erupert, I had a rattle that came from starting up too. I found my cross member hitting my exhaust. The exhaust finger was fine, but I found that I put my cross member on backwards when I put the SYE on my T-case. There is a groove in the upper part of the cross member that is made to clear the exhaust. If this groove is not where it should be, you will have a noisy ride.

With your problem, I might venture to guess that its coming from under the hood. Check the clearance around the fans. If the shroud is loose you will hear it. If something is in the way, you will hear it. Easy to fix.