1998 Chevy S-10 Gas mileage horrific

what did u do? and how much did the gas mileage drop.

im not understanding what your trying to say.

Some time ago I needed to change the air filter on my 1998 Chevy S10. With the late hour and being in somewhat of a rush I inadvertently removed the cover of the throttle body as this is where the air filter would be on my 1993 Chevy 1500 - center of engine compartment with the carberator. Unfortunately this is not where the air filter is located on the 98 S10. When I realized the error I immediately replaced the cover and removed the correct cover on the air filter in the lower right-hand corner of the engine compartment. Afterwards an intermittent high-pitched whistle developed and the gas mileage dropped. The usually 18 to 20 mpg became something more like 12-15 or, perhaps, less. It cost so much to drive that I have parked it until I can locate the cause. It seems as though I may have somehow created a vacuum leak. I had thought it may have resulted from a broken or warped seal but have been told the throttle body has not seal or gasket.

can you get a picture of what you took off?

there should be a gasket on the throttle body.

with vehicle running take a stethoscope or a piece of fuel line and listen to where the whistle is coming from.

was it properly torqued back on? all vaccum lines connected?