whats wrong with my car?

[OnlyNeed4]

I have a 1990 celica st. it ran great for the first 3 months i had it, now it is really acting up, i have taken it to two different shops to have them fix whats wrong with it and neither of them can tell me. first, when i start it up in the morning it idles at about 2000 rpms, after about 2-3 minutes, it drops to around 900 rpms and barely seems like it is running. it kind of sputters. then when i drive it, it accelerates normally until it hits 3000rpms then pauses, and then continues accelerating, it hesitates at 3k rpms for roughly .5 - 1.5 seconds even at full throttle. it is a 5 speed, and it does that in every gear. and then i started noticing the oil lit will come on at idle, if im at a red light and put it in neutral, the oil light comes on. now it stays on until i am over 2500 rpms, once i reach about 2600 rpms the oil light shuts off. i have no clue what is wrong with the car, and no one else can tell me. if you have any opinions or comments please let me know, i would greatly appreciate any help at this point. thank you

 

[BUCK]

I say Vacuum Leak on Intake somewhere - Get a BIG spray can of WD 40 with the fine red nozzle & hunt for your Vac leak - It'll race up when you find it - (you can use Gumout too but that chokes it out when you find it) - Start around the Throttle body Throttle plate Shafts.

Good Luck.

 

[psi on u]

i would say yea a vac leak ...i dont know bout the pause in gear does it do it at wot ....the oil light well im sure its loosin pressure and its not pulling enough with that weak idle (vacume leak maybe ) and its not hitting the sending unit ?? then ur getting up to higher rpms and its pulling more oil ...hence the light goes off
just my guess
good luck