So I was stopped today for some road construction, and while I was waiting I shifted into park. The truck was running fine until I shifted it to park, then it started idling rough. Back into Drive, ran fine. Nuetral, rough idle. Not quite sure what it is. I had P0401 and P0402 codes, both mass air flow codes, first one being mass air performance, and second code mass air voltage. Faulty solder job on the finger stick. Corrected that and still the same problem. I am thinking it could be the FPR, but the tranny shifting part of the equation has me perplexed. Could it be TC shudder. I know my TC is in pretty piss poor shape and the whole tranny needs upgraded, but $$$$. So any help you guys could give me would be great.

p0401 is and egr code. egr flow insufficient to be exact. no 402 code in there. maybe a 404. the 401 is detected by the pcm by using a maf value change to see if the valve is opening and closing during the test cycle. your problem sounds like it could be the regulator. or an injector going bad. have you changed the fuel filter lately?

Might have got the code numbers wrong, but they were both maf codes. Fuel filter is fairly new, but could probably be changed. Just can't figure out the nuetral/park vibrations.

I am having the same exact problem. I changed the fuel filter today ( it had roughly 8000 miles) but it didn't help. I can also feel the vibrations just a little when stopped in drive, but not nearly as strong. I haven't checked for codes but I do not have any lights on. I'll see if I can figure out how to check them with the predator.