I have a 2002 Pontiac Grand Prix.  Over the last few
weeks i have had trouble with the can being jerky while accelerating also i tends to do this more the warmer the car gets IE: runs good in th am but by lunch time it's acting up. Also i noticed this morning that the tranny didn't seem to be shifting from 3rd to drive please help any advice will help.  Thank you.

Could you give me a little more info please. Do you have any
engine light or codes stored that you know of? What is the engine size and mileage of the car. Also, at what speeds are you having the jerky feeling. Thanks. Will try to give some help after your reply, SF

i have no codes to give sorry.  The jerky feelings happen at all ranges but mostly take off
from 0-50 i have even felt it with the cruise set at 70mph.  The check engine light comes on and then goes off from time to time i had it hooked up once and they told me in showed no
code so i just thought it was the gas cap.  The engine is a 3.8 series 2 also the mileage is around 120,000.  Also when the car jerks i would describe it as wanting to just die the TACH will drop some then pick right back up when it does this it dose not rev higher though leading me to believe that the tranny is not slipping but like i said earlier it docent seem to be shifting into drive from third.  At 60 mph the rpm's are at 3000 when they were normally at 2000-2300 misfire is helps and thank you very much for your time.

OK, thanks. Well, any time the check engine light comes on, there should be a code as current, or in history, even a loose gas cap. That is really the key to diagnosis. Just by you descriptions, sounds like you may have 2 or more things going on. A common problem for the jerky condition is a misfire in 1 or more cylinders. Will need to have the ignition system check- plugs, wires, and also the fuel injectors. Plug wires and coils are a common area of problems on the 3800. May want to view the 'hints,tip,diag.' page to see a pic of 'ignition coil inspection' to see what a bad coil usually looks like. Another concern could be a plugged catalytic converter. They cause a poor acceleration condition (see question #48 from the Q & A list for a grand prix with a similar condition). Some engine driveability conditions can cause odd shifting depending on the engine problem. All goes back to the check engine light codes. Coil inspecting, pulling trans. Dipstick and check for a nice red color and not a dark burnt color/smell are some things you can do yourself. After that, getting the codes that are probably still in memory is the next step.
Corroded ignition coil and spark plug wire causing engine misfire and check engine light.
ok so i took it to the dealer and they told me that the catalytic converter is plugged and the map sensor is bad which is the reason it is not shifting right.  Then they told me that the recall on the converter ran out at 120,000 and i have 124,000.  So my next question is will the can run properly with out the converter or are there sensors built in to it?  Also how do i change the map sensor?  Car is a 2002 Pontiac Grand Prix.

1- It is against federal emission standards to run a car without converter.
2- With a converter removed you will definitely have a check engine light and codes. The oxygen sensor behind the converter monitors efficiency. You will get oxygen sensor codes, and possibly driveability concerns because the computer will be trying to adjust air/fuel ratio after seeing incorrect readings from post converter oxygen sensor.

I will attach a pic of MAP sensor location and send shortly
2002 Pontiac Grand Prix Catalytic Converter Codes- No Engine Power

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