1997 Tiburon CEL & multiple codes
 

1997 Tiburon base L4 - 1.8L automatic 195,000 miles. I had been having a problem with engine idling periodically at 3000rpm. Changed out the TPS and that seems to have resolved that. Then yesterday the CEL came back on. Tester shows multiple codes. P1123, PO441/442/446 and PO304. So I am going to change out pluga, & wires, fuel pressure regulator, mass air flow sensor, intake air temperature sensor, and both the upstream and down stream O2 sensors. I am also thinking of replacing the vapor canister purge valve & canister, but I am not sure where they are. Oh yeah, sometimes I smell fumes in the cabin. Thoughts and suggestions? Also once I replace all these parts, how do I clear the codes and reset the light?

The "tester" or scan tool can clear the codes which will turn off the CEL.

Well Crap!
 

So I changed out both O2 sensors, the fuel pressure regulator, the spark plugs and wires, the Air flow sensor (both the big one and the little one in the air filter box) and I still have a CEL! I used the tester to clear the computer and it went from a red light to a green light and said all the codes were cleared but when I start the engine the CEL is still illuminated and when I put the tester back on I get the same 6 codes. (maybe the tester is not really clearing the codes?) I even tried disconnecting the battery to see if that would rest everything and I still have a CEL. Anybody got any ideas? I just spent several hours and $500 and still have a CEL. On the plus side, the car is running better than it has in a really long time!

Code P1123 is long term fuel trim error
Can be caused by faulty O2 sensors?
or, can be caused by leaky injectors or fuel regulator?

Codes P0441/442/446 are evap codes
Sometimes a loose gas cap can cause these codes?
or, it has something to do with purge valve or vapor canister?

Code P0304 is a misfire code on cylinder 4
Having a leaky injector on cylinder 4 ????

After clearing the codes, use the scan tool again to check to see if it has cleared the codes?

As I said in my "Well Crap!" message, I have changed most every part available. I find no leaks on the injectors, gas cap is not loose. I have replace the pressure regulator, both O2 sensors. About the only thing you mention that I have not done is the purge valve and vapor canister.

I understand your frustration.
But, fixing cars is not about randomly replacing parts and hope one got it.
Tests need to be done to evaluate the problem before replacing parts
Otherwise, it can get quite expensive

What I mentioned are just some possible causes
Please don't go about replacing parts on my suggestions
My hope is that you will be able to test to find the real problem and get it fixed

How do you know if the injector is leaky or not?
Leaky as in leaks fuel into cylinder when it is suppose to be closed
A leaky injector on cylinder 4 can give you misfires
Also, it can affect fuel trim numbers short and long term

Good luck to you