When i start my bmw it backfires a lot & bunny hops with no power. When it does get a bit of power as soon as i get near 3000 revs it loses power again. Accelerator 2 the floor it wont go faster than 40mph.

tmiming belt, you need to change it!

It sounds like you might be out of time, how long has it been since the timing belt was changed?

From what you are describing (and it sounds like you have an AUTOMATIC transmission), it is downshifting to a lower gear because it is losing power.
Have you changed the fuel filter lately? (Guessing not.) Do that first.
Once you have changed the fuel filter, see if it's better. If not, move on to troubleshoot fuel delivery issues to make sure there isn't contaminant in your fuel or an obstruction somewhere.
Once you have eliminated that, move on to the transmission. Have you replaced the fuel and filter in it within the last 30,000 miles? No? DO THAT.
Now, if your 323 has the MANUAL transmission, the clutch is slipping... but I'd still recommend checking all of the other stuff above, just to preserve your vehicle. Best of luck to you!

You can use bmw icom to do the troubleshooting

unlikely
back firing is timing , valves or crossed plug leads
could be a serious vacuum leak

I don't think you really would expect someone to guess at all
those symptoms, over the internet

I will say you provided lots of things to think about

Most poeple don't even provide the make of car

Only a possible,so don't throw parts at it
Have it properly diagnosed by a repair shop

The bucking (bunny hop) could be a bad EGR Valve,
along with other issues,such as cylinder misfires as well

The gurgle is not something your hear about,so hopefully
your not low on or loosing coolant,check that & check for leaks
& make sure the heater works okey & it doesn't overheat

if that 2000rpm is start up from cold,,,its still a bit high! but only a bit,,,should be nearer 1500rpm cold out of gear,,,,
when warm it should run at about 850---900rpm-----out of gear-
950rpm for an auto out of gear,,
in gear an auto will drop to about 850rpm so that the motor wont stall when holding the brakes down i would take the car back,, but they may wont it over night so they can set the revs up from cold,,i have a felling that auto choke is still playing up a bit

best bet is to go get any codes that may be stored in the PCM. This will take alot of the guess work out of diagnosing it. Or remove the spark plgs and replace them.. If you have 50,000 or more this could be the cause but a code may tell you which one is the issue

Several things but 2 occur to me. did it have ample oil and water, and, did it do this while the rev counter was up high?. The first you can sort, the second, it probably has a rev limiter over which , the engine will not go. Slow it down a bit and it it should be back to normal.

SOUNDS LIKE CRANK SENSOR OR CLOGGED FUEL INJECTORS