toxxic98

Hello,
I am new to this forum and am looking for help for my Stang. I think I posted this message in the wrong spot before so I decided to post here too. I have 98 GT that I have recently swapped out the non PI motor for a donated motor from lightly used 2002 GT. I have been having problems with the engine idle, for some reason it wants to stay reved high after you rev it up over 2500 RPM it takes forever for the engine to settle back down to normal idle. Even while driving the car and comming to a stop we started to notice the the car was getting hard to stop. So I tried to put the car in nutral and noticed the idle was way too high, causing the car to pull and be hard to stop. I have checked everything I know to this point. I did have a C&L cold air pipe and MAF with 24# injectors that I thought might be causing the problem so I changed back to factory MAF and 16# injectors and still had same issue so changed the IAC motor and checked voltage it was ok but still no change. I am out of ideas, can someone help with this issue?

Thanks

Mike