aode08

yeah I wont be there longer, no work and too many mouths to feed. I got a 8-5 m-f offer repairing ADT security Fleet Vehicles and Assisting with home alarm installs when shop work is slow.

Salary non hourly, and I can live with that, wish me luck, and Ill be starting back into College Evenings,come winter, cant wait to party and the chicks love that stang!

samseed101

That is correct. Basically, your car uses the O2 sensors to see if you're running rich or lean. it does this by adjusting the mixture up / down until it get's the sensor to "switch" from rich to lean or vice versa. Once it switches, it knows that it has gone too far and it goes back teh other way. So if you had a wideband sensor, you'd see your AFR constantly hover around stoich. It would bounce up and down over and over again.

Now if you are too lean, then the car adjusts the short term fuel trim and adds more fuel until it finally gets the car to switch. If it notices that in certain situations, it constantly needs to add more fuel to make the sensors switch, then it will mark that and add a long term fuel trim so that in the future, it will be right on the money. The same goes for running too rich.

With a vacuum, leak, there was no way to accurately measure exactly how much unmetered air was leaking into the engine. So the short term and long terms fuel trims would be different and would constantly change. Basically, teh engine would never realyl know what to do and would spend all day playing "catch up" while it tries to figure out what the problem is.

Yes, you should feel the difference when you get it fixed. Depending on how bad the leak was, it could make a huge difference. Did he say what you vacuum level was at idle? If it was that bad, i'm guessing you were pulling 10 inches or less.