I have a 91 camaro z28 1le 5.7 tpi
when I get on the freeway for a while at about 50+ mph my service engine light comes on but nothing with performance changes. When i stop and turn off my car it doesnt come back on around town, but right when i hit the freeway it lights back up. what could the problem be.
please lmk

 

EGR valve more than likely. They are good for this. Check the vacuum lines to it and the solenoid for cracks, or melted areas, etc. If the lines are in good shape and not deteriorating, then the EGR valve itself or the solenoid is bad, or both. First thing you want to do however, is pull the code out of the computer.

 

hey thanks for the help but im a complete noobi with my whole car, i got it like a month ago so could you explain to me where the EGR valve is.
thanks.

 

first you want to pull codes & see what comes up.

this is the ALDL connector,

http://images1.snapfish.com/346%3A%3...5%3A%3C7ot1lsi

to pull the codes start with the key off & put a jumper wire or paper clip between A & B in the ALDL & then turn the key to the run position but don't start the motor.
now count the flashes from SES light.
you should get something like this, flash,.. flash flash, it should do it 3 times total, thats a codes 12, you want to see code 12, if you don't get a code 12 then something is wrong.
after it flashes code 12 3 times there will be a little pause & it will start flashing the next code.
a codes 32 which is for EGR would be like this, flash flash flash,.. flash flash, & then repeat 2 more times.
write down all codes you get, after it has flashed all stored codes it will start over with code 12 again, that means you are done pulling codes.

if it does have a code 32, look here for help with finding your problem.

https://www.thirdgen.org/egrdiagnose

 

O2 sensor would be high on my list as well. Had the exact same problem a few yrs ago. The codes should tell the story though.