p1506 code on 97 cobra

It is an IAC code but, the 1st procedure for this code is check for vacuum leaks. including in the IAC gasket seal or valve assembly. If you have another IAC you may want to try using that one if you don't find any leaks.

OK - assuming there is nothing else wrong - you can do this yourself.
First - make sure your battery cables are clean and tight. Its common in Ford's computer stategy to keep a higher than normal idle if you have bad connections. It thinks it needs to keep idle up to charge the battery. If that doesnt solve your problem - remove the negative battery cable (not the positive) and leave off for a minimum of 5 minutes. This will reset the PCM to its base values. (Also known as resetting the KAM - short for Keep-Alive-Memory.) This should also clear the code providing you dont have a hard fault in the IAC system. If it all returns to normal - your good to go. If it doesnt and the code returns - take it to a shop that has the Ford factory scan tool called "IDS". Its a windows based software program that allows the tech to bi-directionally control the IAC motor and check for smoothness of operation. This platform also allows the technition to check and see if a "flash update" is available to correct the issue. He also has the ability to reflash the PCM over from scratch and wipe it clean. Its the same priniciple as reformating the hardrive and reloading windows on your home or laptop computer.
Another senario is the possibility of a PCM replacement issue due to improper jump starting of the vehicle. Alot of strange things happen under this condition. Its a very real scenario. I assume your wiring is good because you claim it does return to a normal idle after a bit. It appears to be a "stategy issue.
Good Luck

First of all, NICE Cobra!, I love the green!
If you cleaned the throttle body and MAF properly, put everything back together properly, I'll bet it's a vacuum leak. The car is a 98 model. It's over 12 years old, so the hoses will be kinda dried out and hard. Check the large ones first.