OK so the other day the SES light came on on my 1994 Z28. This occurred right after I fueled up so I though it was a loose gas cap. Checked my cap, it seem tight, but the light went away so maybe it was the problem. 30-40 miles of diving later the light came back. Just for the hell of it I loosened and retightened my gas cap and the light again went out. Lo and behold 30-40 miles later SES light comes back on. I loosened and retightened the cap, restarted the car and the light was off.

I haven't be able to run any codes on it because I cannot find a shop around here with an OBDI reader. Each time I loosened the cap there was a hiss signifying to me that there shouldn't be a fuel pressure problem. ANY IDEAS WHAT COULD BE CAUSING THIS? And why my gas cap is making it go away.

 

Messing with the gas cap could be a coincidence, and just plain ol turning the car off and on is what's temporarily clearing the error. See what happens with an off-on, without touching anything else.

 

Sorry, I should have mentioned that in the original posting. I tried just a plain 'ol off/on and that didn't clear the light. That is what lead me to try the gas cap the last time before posting. That is what has me befuddled. Otherwise I might have just chalked it up to coincidence.

 

Then it quite possibly could be your evap system, but not necessarily with the gas cap itself. Do you have a spare cap you can "borrow" from another car, to use and rule your cap in or out?

 

My SES light comes on randomly from time to time. Goes off anywhere from 5 mins to 15 minutes later (while driving). Good luck finding a place that can read codes from these cars. I think it is d@mn near impossible.

 

WELL!!!!!!!! Did a little more fooling around. Found out that the light would come on while the car sat and idled for a few minutes. This was CONSISTENT. Each time it came on I would try different ways of resetting the light. Turns out that the gas cap WAS a coincidence. Now that I figured out that the problem was indeed a light each and EVERY time I sat and idled for a few minutes, I decided to dig into it a little more since I am now home from work.

Hmmmmmm!!!! What has changed on the car lately. Well, I did put on a new crankcase vent hose. That shouldn't do anything to the system. I pulled the throttle body when I did to clean it since it was pretty nasty. Cleaning something shouldn't throw a code either. Perplexed I did what any guy would do and popped the hood and stood there looking at my engine.

Wait a minute. . . what is this?!?!? Turns out when I pulled the intake elbow to get to the throttle body I forgot to plug back in my IAT sensor. I plugged it back in and started the car. I then went to close my hood and hear a distinct hisssssssssssssssssssss. Hmmmmm. Well lookey here looks like I also forgot to reconnect one of the vacuum lines to my throttle body. I slapped that hose back on, checked to make sure my SES light was still out, went for a short drive, and let it idle when I came back. Still no SES light.

I guess that is why they call them IDIOT lights.

 

lmao. You know, it would have been helpful if you had first said, "all was fine until I just did this......"
First thing I usually say is, retrace your steps.