Idle/ Acceleration Issue

[JollyRoger]

Hello all,
New to the forums, but have been here over the past 2 years checking out the forums and tech pages for advice. Great Site!!! I have a 2003 Volvos 80 T6 now with a 140,000 miles on her and going strong. We bought the car 2 years ago with 66,000 miles and have been trouble free with exception of maintenance issues, radiator leak, front and rear links, broken headlight from leaking gasket and sub zero temps, struts/ mounts, etc. All work done by myself.
My current issue has happened before, and then went away, now it's back. When I start the car from cold, I allow it to warm up for a minimum of 2 minutes in summer, and 3-5 minutes in winter. When starting, the idle goes to 1500-1800 rpm's and then settles down to between 600-800 rpm's shortly thereafter. As of last week, I started her up and the idle only went to 1000 or so and settled immediately to 600-800 rpm's as if something were restricting it from opening it up. Now I know it's getting cold out here but this has happened on warm days of that week as well. Upon driving, the acceleration seems like it's being retarded by something. I am very easy on the gas pedal in regards to acceleration (think foot on an eggshell) so during most of the year i get a response immediately, However during the time this issue occurs i have to put my foot a ways down for it to get anything and even then it is really really sluggish. I have noticed during this that my gear shifts are much smoother when this issue occurs. I also just recently got a leak detection sytem code which went away after a few days with a new fuel cap from Volvo. The old one was garbage. The code came back again, but went away again after another fill up. Hasn't been back on since and it's been nearly a month. I have no clue. So if any of you have any ideas of what the possible causes could be, please feel free to chime in.
I wanted to add my maintenance practices I use to rule out any possible causes. I use 5w30 full synthetic from NAPA (Valvoline) year round, and have had no problems with it. I just finished my second treatment of AutoRX. I change my oil every 3-4000 miles, I use Mahle oil and air filters, I flush my tranny every 20-25k using a new filter and gasket every time and I use Valvoline Dex6 full synthetic. I just replaced all the coils, replaced the plugs with Volvo plugs every summer. I change the fuel filter every summer. I occasionally clean out the turbo boost valve with CRC electronic parts cleaner as it dries quick and leaves no residue. My MAF sensor is original, cleaned regularly with CRC MAF cleaner. The sealant holding the cover to the MAF was deteriorating last month so I cleaned all the gunk out and resealed it with silicone gasket. Hoses are in good shape overall.
Like I said, feel free to chime in and any info is greatly appreciated. Thank you.

[537playing]

It maybe your MAF sensor. Try disconnecting the MAF via its connector and run the engine. Search this site for other tests regarding the MAF.