2000 Dodge Neon please help on idle issues!THANK'S

Hello and thank you in advance for looking through this. I have a 2000 neon I just bought for my son and I replace the timing belt, water pump, alt. Belt, powesteering belt, upper and lower engine mount, trans fluid and filter and did a full tune-up. My problem is that the car runs really good, engine sound really great and shift fine. When I come to a stop, the idle goes down a little and the whole car vibrates, when that happens I put in neutral and put it back in drive. The vibration stop. I cleaned the throttle body really good and clean the iac valve but no luck. It's not throwing any code. I know I did the timing right. I check for a vaccum leak only found one but that did no solve the problem. I do a lot of side job on cars and this really is giving me a head ache. Im thinking of replacing the iac valve but don't know if that will help. Any reply or help please.