i sort of had that problem (hissing, CEL) when i installed my CAI. comes to find out that i didnt take my time and the cuff link wasnt on the TB all the way and i guess it was basicly like i didnt have a filter on it. to much air was getting to it to quickly and it would shut of and throw a CEL. check all your points of connection with the CAI and also make sure that your plug wires are pushed all the way down getting a good conection...

 

I forgot to mention that you can do the key dance if you have a 420a to get a MIL code. You turn the key on - off - on - off - on and leave it there. At no point should the motor start. After the third time turning the key to the "on" position keep your eye on the CEL light. It will blink one number, pause, and then blink for the second number giving you a double digit code. It will then take another pause and either give you more double digit MIL codes or blink 5 - 5 = 55, which means "end of code".
From there, you can find the Mitsu/Chrysler definition of that code. Keep in mind that those double digit codes are general codes and deals with systems. If you want specific definitions of the issue, you will need an ODBII code reader. The ODBII will give you specific parts and not just the A/F system (that's just an example).

 

So it has been a little over 2 months since I mentioned about my CEL coming on. I'll give an update one everything that has been done. I replaced my whole exahust from headers to the exhaust tip all done by an auto shop. I had a new transmission and clutch placed in along with new sparks and wires. My speedometer/odometer guage does not work, but everything else does. My CEL light has been on for a while now, rarely it goes off for about an hour and then it will come back on. (It's only turned off maybe 2-3 times now.) I tried the Autozone place a while back but they said I wasn't reciveving power to the OBD not sure if it is I or II, maybe I could go back and tell them to try the other since it might get a reading. All my fuses are fine, I have no idea what is setting it off and the light is getting on my nerves now. Any help would be great. Thanks!

 

Check the speed sensor on the transmission. It's a good chance that the mechanics screwed up the plug and it's not seated completely or they broke the speed sensor. You have a 420a right? I looked back at your posts, but you never clarified. If it is a 420a, then do the keydance... on-off-on-off-on; count one second before each turn. Watch for the CEL as it will blink. Count the number of blinks. BTW, it will blink the first number 1-9, pause, then the second number 0-9. It will then pause and repeat. If there is nothing else, it will blink a 5 and another 5 = 55, which means it's finished.
Let us know.

 

is a 98 eclipes obdII?. what are the torque specs on the header and retorque them down see if that helps at all.

 

96 and up is obdII.