Question: Car accelerates bad need help?

hi guys need some help with my car trying to figure out what the problem is , the problem is while driving when i put my foot down on the gas the car wont build up revs or speed it just struggles to accelerate sorta shakes or something then after say 4 seconds of holding my foot down the power comes back. Was at a stop light tonight and my idle was bad dropping down like it wanted to stall then had trouble taking off in 1st gear no power, but later on the car was driving good so isn’t as bad when i been driving car for a while i think, also could smell something weird when driving before like burning rubber but that was only one time.

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The things i have recently done to the car is replaced timing belt, starter engine , oil change , replaced air filter, replaced fuel filter, fixed some leaking fuel hose and has been serviced . dunno what else it could be was thinking maybe the catalytic converter?

thankssss