help new problem on 98 cherokee 4.0 when warmed up everything great

When you say slow start do you mean it turns over slowly or you have to crank for a long time for it to start?

good fast cranking just slow to fire.

Try cylce the key on then off a couple times then start the engine. Any differance? If so you have a possible stopped up fuel filter or a fuel pump starting to go. High idle? How high? It is normal to idle at about 1-1200 rpm when cold.

Are taking about when you first start it you it automatically revs up to like 1500 rpm for 2 seconds then drops down to a normal cold high idle. If so below will fix your problem.

Clean your throttle body really good. The best way is to go buy a throttle body gasket and take it off and clean it on a bench with a tooth brush & cleaner. Also remove the IAC (Idle Air Control) clean it really well it is probably sticking and gummed up. Also check and re-adjust the TPS sensor.
It is a very easy job.