Hesitation when pulling away

[anubis1980]

Hi i have a 99 Yaris 1 litre. Where to start?! well a while ago i noticed the performance had dropped and my mpg had dropped too. took it to a garage and he said it sounded like it was misfiring. so he hooked it up to get tested and he couldnt find any error codes. he said it also drove like it was flat...

he cleaned everything (his words) well when i got it back it was the same. i left it over night woke up went to work and the mpg was back to where it used to be ages before! so he had fixed it. well the last couple of days ive noticed when pulling away the car hesitates, then picks up, mpg seems the same and ive also noticed (as he did ) a noise that MIGHT be hissing although i cant be sure. the plugs are new, new air filter. Im stumped ive cleaned the MAF sensor, checked plugs again to make sure they are all ok (all same light tan colour). So if anyone could please throw some ideas my way id really appreciate it :)

Brett.