XJ erratic idle and ECU issues

hi guys new member here and I'm happy to say my 1997 Xj has 300k miles and I'm starting to have issues that I expected to have one day. I broke down a while back got towed ect. My distributor went ok so I replaced it set it at TDC. So my Idle was erratic and after getting shafted by a few mechanics sensors were changed, ignition harness was changed, and my truck continued to run like S--T. Then suddenly she started to backfire as if off timiing. Suddenly there was no spark to get started, Got shafted yet again by a so called short specialist. No short was found. I towed my truck away because I got no answer to my problem. I asked another XJ owner for his opinion. He told me it could very well be my ECU. So I went and bought a refurbished plug and play unit with a lifetime warranty and I installed it. To my surprise my truck started right up. But the Idle started to rise just over 1 thousand RPM. That Idle is too high. Can anyone give me some advice here This XJ is my BABY I have alot of money invested in her and she has been great to me for 18 years. I just want 1 more year. What can I do? is it the ECU? does it need to be reprogramed? I appreciate this site for letting me post my problem here. But most of all I appreciate the members who take the time to read my post and give this old fellow XJ owner some help. Thank you

Remove the IAC valve and clean it out. Its probably just gunked up.
While you are at it clean the throttle body up real good and it probably would not hurt to run some seafoam threw it ether.

Should fix your problem.

Might have an open vacuum line somewhere from all the hands on it

I did clean the throttle body,and IAC and changed my tps. she was running fine before my distributor went on me. thanks though. I've seen people use that sea foam and the smoke it creates.

the diagnostics always states crank and distributor and their both new. should do the spray throttle cleaner over the top of the engine? what about the new ECU?