Rough cold idle, not exhaust manifold

I have noticed that recently my Jeep (cherokee '92 limited) doesnt start the way it used to. It used to idle slightly high for a few seconds and then drop to the normal rev's. It stopped doing that recently and I thought it maybe had to with the exhaust manifold leak getting worse. To get rid of the noisy run and maybe also fix that different start-up behavior I have replaced the exhaust manifold this weekend. This is what I find:

1) The high idle has not returned.

2) When started, the engine runs very rough for about a minute or so and then suddenly switch to a very smooth run.

So these are two questions actually.

1) What happened to the high idle at startup? What do I check/replace for that?

2) Why does the engine run so rough when cold and then suddenly change to a smooth run? Any clues? I was hoping the exhaust manifold was causing this but it turns out it isn't.

FYI, I have recently replaced plugs, oils, fuel filter, coolant. When I took off the intake manifold I did notice there was a lot of black carbon deposits there. Could that have anything to do with it (injector blocked)?

When the engine is running smooth the new manifold is great and makes me happy. Hope anyone can give me some clues to my questions! Thanks!

pull out your idle air controller and clean it up. it's located 90 degrees to the linkage on your throttle body.

it's basically just a little plunger that controls the amount of air that bypasses your throttle plate at idle, therefore regulating your idle speed. when you'd start you vehicle it purposely overcompensates for a second until it adjusts itself down to the preset RPM (800rpm).

what happens is over the years fine bits of crud and dirt get past your air filter and deposit themselves on the said plunger making it stick in the hole causing either really low idle or a wondering idle.

you can just take the two torx screws out and blast the plunger and all that with some good throttle body/electric parts cleaner and spray down in the housing and hit it with a toothbrush or something to clean up all the gook.

Thanks! Will do!

Do you have any idea's on the rough idling? I think that's unrelated to the fast-idle run and really haven't got a clue. It almost sounds as if the engine is missing a beat and is overall not running well.

This weekend I wanted to clean my idle air controller as suggested. However, I couldn't get the original gasket from the autoparts store (so I decided not to upen her up yet). Is is ok to just cut a cardboard gasket to fit the connection and add some liquid gasket to seal it up? Or should I go to the dealer to get the original gasket?

Thanks, --Tim