[Topher12]

I have a 95 that has an idle/vacuum problem. In idle it will run fine until a point. then I hear a sucking sound and the idle goes to crap. If i hit the gas a little it acts fine for a minute. When I take off the air filter assembly it seems to be the IAC. I have cleaned this more than once, but have not replaced yet. It also has a problem while driving. If Im going down the highway my HVAC will change from blowing out the dash to blowing out the defrost. When I let off the gas it goes back to dash. Also when its hot and the gas cap is tight Im leaking gas from the top of the gas tank. I have been loosening the cap when its hot to keep from building pressure in the tank. Other than that it runs fine. Im used to how it is but want to get it right. Not sure if any of these symptoms are connected. But they seem like they could be. Truck has over 200k on it. Also I havent changed the plugs and wires on it yet. Its my next thing I want to do.

 

[Lazarus Truck]

Hi Toph! The clue that the diverter is changing modes during steady driving is a big clue. The diverter is run by vacuum. When vacuum is low (during heavy acceleration) or lost due to other means, the diverter is designed to reset to defrost as a safety measure. Yes, you will freeze to death, but at least you will be able to see, is the thinking behind that. I suggest you try a vacuum gauge first to try to diagnose this. About $10 at Harbor Freight. You should have about 18" at idle in neutral, and about 16" in gear with the brake on. This is a good start for a suspected vacuum leak. Lets go from here. Or if you cant afford $10, start plugging all the vacuum lines that you can find off of the intake manifold, and see what makes it better.