Vacuum leak=misfire? Oil light at idle?

[97GSRyan]

Ok, I have a 97 GS non-turbo that I recently bought and it has a few minor issues. The CEL keeps coming on, only on the freeway. I've been to Autozone for it many times and the codes always come up as a random mis-fire on all cylinders. They printed out a sheet of the probable causes-Plugs, wires, injectors, coil, vacuum leak. I've already replaced the plugs and wires, and got a fuel treatment for the injectors. Also, the car runs fine. No sputtering or idle surging. I'm trying to see if there are any vacuum leaks right now, and I was curious if anyone has heard of the Schrader valve leaking? Any insight to testing vacuum/common leak spots would be awesome. I can post pictures of areas or hoses if that's any help.

Also, (hopefully) unrelated, my oil light comes on occasionally. I've narrowed it down to only doing it at full operating temperature at the lowest idle speeds. (750-800RPM) I just did an oil change and I know I'm not low on oil. I do, however, have a very small oil leak that looks like it's coming from the oil pan. My main question is, would such a small oil leak possibly affect my oil pressure enough at idle to make the light come on? As soon as I hit the throttle it's fine.
It's just frustrating because I pride myself in being somewhat mechanically inclined and I'm clueless on these.

 

[crimsondragon]

To do a vac leak test, spray starter fluid on TB seals, vac hoses, etc. If your RPMs go up, that's the starter fluid being sucked in.

 

[97GSRyan]

Thanks so much, I'll try that right now and I'll post how that goes.

 

[ktmrider]

To do a vac leak test, spray starter fluid on TB seals, vac hoses, etc. If your RPMs go up, that's the starter fluid being sucked in.

+1, excellent way to find leaks.

Also, (hopefully) unrelated, my oil light comes on occasionally. I've narrowed it down to only doing it at full operating temperature at the lowest idle speeds. (750-800RPM) I just did an oil change and I know I'm not low on oil. I do, however, have a very small oil leak that looks like it's coming from the oil pan. My main question is, would such a small oil leak possibly affect my oil pressure enough at idle to make the light come on? As soon as I hit the throttle it's fine.

Could be the pressure sensor going bad/blocked or the oil pump is getting weak.
The pressure sensor ( two near the oil filter mount ) is the smaller of the two with an unusual shape, requires a special tool as a hex wrench or socket will not fit.
Put an oil pressure gauge on and see what the actual reading is ( don't rely on the cluster ). The general rule of thumb is 10psi for every 1000rpm, with 10psi the minimum.
First guess is contamination in the sensor port, it's quite tiny and easy to block off.

 

[97GSRyan]

Thanks for the input, I actually searched after posting (oops) and found out how to check my sensor last night. I do have an oil leak that looks like it's coming from the top end, which dripped oil alllll overrr the wiring and connecter for the sensor. Hopefully that's all it is haha. I did see that apparently the part is cheap so I'll probably just replace it to be safe. So given the oil leak, I'm going to clean the hell out of my engine so I can spot the leak :] Of course Autozone had to close for New Year's Eve, so I just got the starter fluid... Gonna take care of that right now and see how that goes. At this point, I hope my problem is a vacuum leak haha

 

[97GSRyan]

So I just did the vacuum test... All the hoses/seals appear to be fine, but there was one spot that raised the idle when I sprayed the starter fluid on it. The EGR valve. I sprayed on the slit-opening in the housing and the idle went up. What I'm confused about is, should that happen? I'm not too familiar with emissions components, so is the EGR supposed to vent/vacuum to atmosphere? Thanks, any input would be awesome.

 

[97GSRyan]

Ok little update if anyone was wondering... I un-bolted my EGR from the head so I could clean it, but couldn't get the pipe off of it to take it out of the engine bay. I just bolted it back together and did the vacuum test again. NO LEAKS WTF And no CEL so far with about 5 mi of freeway

Now for my oil light, I have my sensor disconnected and the light is still behaving exactly the same as when it was plugged in.. Contaminated wiring somewhere? Only thing I could think of