Hyundai Repair: emissions, throttle position sensors, throttle position sensor

Question
Lets see if I can get this correct.
Codes are possible 021 and 003(I think) I know the report read Mass Air Flow and Throttle sensor on the last report. I do not think anyone got rid of the codes. How do you do this? I think the part may have been after market but I do no know how to tell that. (The mechanic says that the parts guy buys a lot of after market parts.) The other things that have been done is changing a coolant sensor, tune up, replacing a valve cover gasket, fuel filter and air filter and power steering hose.
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The text above is a follow-up to ...

-----Question-----
I can not seem to pass emission test. 1999 hyundai elantra that keeps showing codes with volume air flow and throttle sensors. The Volume air flow has been changed twice. I can not pass. Help@
-----Answer-----
Hi, Kathy.  

First, you should check with your local Hyundai dealer to see if there are any open recalls on your vehicle.  There was a recall involving some 1999 Elantras which required the replacement of the air flow sensor connector.

Second, I'll need a fair amount of information to give you significant assistance.
1.  What are the actual trouble codes that are being stored?  This will give me a much better idea as to what's happenning than knowing simply that the codes relate to the air flow and throttle position sensors.
2.  Has anything been done other than replacing the air flow sensor twice?
3.  Were the trouble codes erased after the repairs were performed?
4.  What sort of air flow sensor did you purchase  (factory, aftermarket, used)?

Answer
Neither P0003 nor P0021 are used for your vehicle.  Just to put them into the range of codes which would apply to the things that were replaced, that would make P0103 (excessively high air flow reading) and P0121 (throttle position sensor performace issue).  

P0121 most frequently occurs when the throttle position sensor itself is defective.  But P0103 is very rare.  In fact, I don't recall ever seeing it occur.  If this is the actual code, the circuit for the air flow sensor should be thoroughly checked.  

If your mechanic has the capability of reading the trouble codes, he should also have the capability of clearing them.  If your check engine lamp was on when the car was taken in and out when the car was returned to you, it's fairly safe to assume that the codes were erased.

Since you're not sure of the codes, we should start by verifying what codes are actually present, presuming they were cleared after the repairs.  This will help get a decent handle on what we need to be looking at in terms of possible problems and solutions.