I have a 98 neon sport, has a recently new shortblock(20,000). When you cold strt the car it starts runs a high rev the settles down to idle, or suppose to anyways. it sometimes dies, other times it will barely run, shake the rev and settle down. not sure of the rpms, its my wifes car. I can check more if I have to. no codes. or alteast lights to show anything wrong. i was wanting some hints to why it does this
thanks
Nuwt

 

My first plan of attack would be to pull off the throttlebody and clean the heck out of it with carb cleaner. Even though it's a newer engine, parts like that were probably reused. The IAC can develop a heck of a buildup and be very slow to respond, particularly if the a/c (including defrost mode) is on. You can remove the IAC for better cleaning if you like, just be careful. Those bolts are in there with blue loctite and will snap... Had mine tie wrapped on for 40k miles or so...

Best of luck!

 

In addition to making sure everything is clean and hooked up right and everything, I'd also check to make sure the engine and PCM match... Your sport might've been DOHC, and the motor might've come out of a SOHC sport (or the other way around). It also might be a problem if they're different years. Depending on which years, there might be more or less of a difference, but I think there's still a little (95, 96, 97-99). There's probably a lot that could be different, even if everything is clean and connected properly.