Fix vapor lock

SOURCE: 1990 vette runs fine after 15-20 min won't start then wait 20 -min runs fine again until i shut it off

I had the same problem. Turns out,( and I didn't believe it when I was told) but, my problem turned out to be cheap (inferiour) plugs and wired. I was reccomended to use NKG plugs and Borg-Warner wires.

SOURCE: Acts like vapor lock

when they went to fuel injection the fuel that was not used returned to the tank thus cooling the fuel and ending vapor lock, my question is did you do a fuel pressure test? and di you do a fuel leak down test? and the first thing I would do is change the fuel filter. with ethanol in the gas it kills the filter. I have to replace mine every three months they just plug up from that junk. Other than that the only other thing would be a coil breaking down when it gets hot the coil shorts out when cool it starts so check those things first. be sure fuel pressure is 50 to 60 PSI and does not drop below 30 PSI for at least a minute, if it does the fuel pump check valve is bad, also the fuel sock could be bad as well.

SOURCE: vapor lock?

keep the fuel tank at least half full.....it may helps cool the pump

SOURCE: Won't start after being shut off in hot weather

try a new gas cap

SOURCE: 2003 sorento. after driving 55-65 mph just fine

As much as your going to hate hearing this, I have to lean toward the transmission. Pressure build up in the transmission causing the torque converter to work harder and causing your problem. If you haven't changed your filter and fluid in over 50,000 miles I would have the transmission checked. You also want to have the PVC valve on the Valve cover checked as well. If that has oil build up it will restrict vacuum, sometimes this takes some driving time. Check this first as it is a $10 fix. It is certainly possible to have the vacuum test good even if there were a problem wince it wouldn't show bad unless you had the same conditions that exist when the vehicle is moving and your problem presents. The same goes for the fuel pump and return fuel lines that go to your canister collector. Charcoal in the vacuum line is an over pressure indicator. A lot of these test can only be done if you re-create the problem. Fuel pressure no problem as they have testers that can be attached to the system to test fuel pressure through out a test drive. Vacuum is a little different. Also, and I know I'm adding a lot of possibles and apologize for that, it could be a faulty MAP sensor. Again, this resets when the engine isn't running so it would only present when the problem was occurring. This would be an indicator of a sludge problem in the engine as that will gum up the MAP sensor.