Originally Posted by TexasTrevor
Yes it was doing this when I got it back but I just thought that I did something wrong when I put it back in. But after driving it 1500 miles and going back over everything I can't find anything that doesn't look right. I know that the place that rebuilt it for me normally does an excellent job. The motor is under warranty so I guess I'll give them a call and see what happens.
Honestly did you try replacing your throttle position sensor? This sensor tells the IAC when to operate and gives the computer a refference for how much fuel to give the engine at a given throttle position. In some cases it will make the rpms go up or down by 2-300 rpms while driving even!
If the motor runs good & consistent even at 1100 Rpm, I would not suspect a blown plenum gasket on a rebuilt engine, my sisters had a blow out in 4 places and that never ran over 800rpm at idle ever. Pretty much it was 800 at first start up then dropped to about 550-650rpm. Every plenum job I've done has had minor leaks that cause other problems and never once was the high rpm idle one of those problems.
So my point is, if theres even somewhat of a gasket on that plenum, the engine should idle down normal.
I would just for piece of mind, spray some starting fluid around the plenum where it meets the heads and see if the rpms change at all, if so try re-torquing the intake in the correct order and then After checking the throttle body for vacuum leaks and all vacuum hoses, I'll throw a good chunk of change bet on your Throttle position sensor being bad replace is my best advice! which even without doing the rest of the above I'd change anyway.
The only worry on the engine itself I'd have is if they used intake gaskets that have the front & back cork seals, sometimes they can slide even when you use permatex to help keep them in place and when you set the intake on you can move them, along with the intake not being torqued properly in the correct sequence which I suspect was most likely done which brings me back to the TPS replacement and making sure no leaks are coming from the throttle body to intake seal.. If they screwed this up, confiscate their tools and call a lawyer.
My Neon engine swap I did 2 weeks ago was pretty scary! my parts motor I put in had been sitting behind my dads garage in the elements for 3 years and on its first start up it shot up to 8,000 Rpm before we could react to turn it off. That ended up being due to me assembling the plastic intake manifold on the engine in 5 degree weather and the flange became a banana from sitting outside and then assembling it.