Throttle or Oxygen sensor problem?

[Postman1955]

My son's '92 Geo Tracker will idle and accelerate normally. However, once the rpm's reach 2500 +/- the engine will immediately drop to 1800 +/- rpm's and then accelerate until reaching 2500 rpm's again. If the vehicle is in motion the same procedure will occur when each gear is at it's max (again usually @ 2500 rpm's).

Could this be caused by a bad oxygen sensor reducing the fuel mix or is it possible that there is a "bad" spot on the throttle sensor which shorts out when reaching the rpm threshold mentioned above?

Are there any tests that can be performed to eliminate or determine which it may be?

Or, could it be something totally different?

[1995 geo tracker]

is the check engine light on?

[Postman1955]

Yes, it is but unfortunately there is no connection for hooking up a computer or other device to determine the reason it is on. Any suggestions?

[1995 geo tracker]

the connector is under the hood near the battery infront of the main fuse block , go to your local parts store and grab a haynes manual , it wil show you how to test and where the connector is . on a side note , i have a 95 tracker with a blown engine that i am parting out or selling as a whole , the top is less then a month old and the tires have less then 5k on them , the body is in great shape with no rest or dents , so if you are looking for parts or just want the whole thing let me know