major studdering and wont rev up

my 2000 jetta in the last few months has taken a while (2-3 mins) to warm up in the mornings when i first start it up (regardless of cold or warm weather). when i first turn on the car it starts fine 1st gear it fine but when i put it in 2nd it studders some, i drive it 1/4 of a mile to a local parking lot and sit for a munute, then its fine for the rest of the day. the check engine light has been on for a year or so (when i got it checked when it came on the computer said it was a bad O2 sensor). due to the recent changes (studdering and taking a while to warm up) i decided to get the check engine light rechecked. the car had 15 codes ranging from O2 sensor to 1st 2nd and 3rd cylinder misfires. i took it in to local garage where they replaced the ignition wires, spark plugs and valve cover gasket. the garage called to tell me it was done, i went to pick it up, the car started find but the studdering was worse than ever and i could put my gas pedal to the floor without it reving up at all. the mechanics worked on in for a while, while i was there (while it was running). after 30 or so minutes the car started reving up regularly when they pushed on the gas. they said they found a loose vacuum hose, i took it home and hoped for the best. i tried starting my car this morning only to find that it was doing the same thing that it had ad the mechanics shop (not reving regularly and studdering). i mean if i hold the pedal to the floor it will idle for 30 or so seconds then rev up to 3000ish rpm's then back to idle... i replaced a couple vacuum hoses, and left my car running in idle for a while and it eventually cooperated enough for me to take it to the shop (but it had to warm up for a good 45 minutes in idle). i dont have a clue what is going on with it. i have recently replaced the fuel filter, the air filter, a couple vacuum tubes. i would appreciate any feedback, and sorry i know the post is long

You will need to have it put on a machine to read the computer. The dealer is the only place I trust to read the computer. With misfire codes it could be many issues(fuel injectors, fuel pressure regulator, etc.)
Franco