Strange Idle

[JIGAWHAAT]

Hey guys
As some of you know I had to can my old engine (97 5.0) for a used 98. Well the swap is done and the donor runs strong as an ox. I do however have a little idle issue. First off I have read a ton of the threads on idle problems. I cleaned the iac and even swapped my old one in there with no prevail. I did'nt clean the maf yet but I am almost sure thats not the problem. Here is what is throwing me off. It idles fine when in gear, drive reverse etc. (auto trans) But whenever I put it in park or neutral the idle drops down and runs rough for a while and then runs fine for a bit then rough. I can be in drive at a red light all day long and it idles like a champ. Any clues?
I am trying to rule out whatever I can here. Its 19 degrees out here so the less wrenching I need to do to figure this out the better.
Thanks in advance
JIGA

 

[JIGAWHAAT]

Well now that its warmer out here I would like to get out there and fix this issue. I am throwing no codes and no cel. She still is doing the same thing. idles great in gear and surges in park or neutral. Any ideas would be great
Thanks

 

[Turdle]

It may very well be a dirty Maf--
Also--You might check the throttle position sensor voltage at idle.

 

[JIGAWHAAT]

It may very well be a dirty Maf--
Also--You might check the throttle position sensor voltage at idle.

Thanks jon
If it was a dirty maf, Would'nt it throw a code?

ps: Any takers on your sporty?
Did you decide on weather you are selling the mounty yet?
See ya
JIGA

EDIT:
The reason I am ruling out the maf is because this idle started to happen after the donor engine was installed. The maf was not touched during the engine swap.

 

[Turdle]

Thanks jon
If it was a dirty maf, Would'nt it throw a code?

ps: Any takers on your sporty?
Did you decide on weather you are selling the mounty yet?
See ya
JIGA

Not necessarily ,if it is dirty it might still meter the air, but be off a little--