Surging???

[TigBitties]

ok guys, i need some idea on what could be wrong. im stumped. I attempted swapping from a y7 intake manifold to y8. but now that i did it the car is surging. the rpms go up to about 2k and then drop down to 1k. i have checked for leaks and cannot find any. i can play with the IACV and when i turn it up to about 2k the motor smooths out and stays there, but if i turn it down it surges again. Any ideas? I have looked over this car 100 times and spent atleast 20 hours trying to find this. Any input could help.

 

[2NRSTV]

You've got to have a leak somewhere.
Check the torque on all the manifold bolts, especially the ones on the bottom. Make sure all mating surfaces are clean. Possibly change gaskets on the Manifold and the Throttle Body. Check hoses.

 

[Doubletap]

Your IACV is messing with your throttle. Mines doing the same thing at the moment. At idle it will stay at 2k RPM and then hitch back down to 900 to 1k RPM. Your IACV is the issue thats causing the throttle response issues. Try cleaning it and what not, if that dont help you will have to replace it with a new one or used one. Just remember new ones cost around $200. I have also seen these go for around $450 new. Try the cleaning option and what not. Also check any vacume lines that are leaking that can causing issues with the throttle at Idle.