91 spirit 2.5l tbi light throttle no power issue

Hi all,my stepdaughters totally stock 91 spirit 2.5 normally aspirated TBI auto trans is down on power and stumbles /shudders on light throttle cruising down the highway and nearly dies under load ,IE climbing a hill,if i floor the throttle it will usually kickdown the trans rev up and go but with lite throttle its dead,no fault codes other than occasional code 21 (oxygen sensor),has 165 000 kms on it(100 thousand miles).new spark plugs,air filter fine,good battery etc

Check fuel pressure. Clogged fuel filter or a weak pump can cause this. Map or TPS could also show same symptoms. I connect a scan tool and see what they are reading and compare to what the correct parameters are.

Also check the MAP sensor. If the computer doesn't read the drop in vacuum when the throttle is opened up, it won't the correct amount of fuel to meet the demand.