vacuum leak = low mpg?

The two things may not be related. Bad gas mileage sometimes is due to the injectors dumping in lots of gas because the sensors think the engine is running lean or the regulator is shot, etc. A vac leak could do that but you would know it cuz the engine won;t idle. Which engine?

That's not a vacuum leak. And it only leaks when the system is being tested. At max once per drive cycle.

Yes, it does idle fine. Also, the last time there was snow, I had the car idling with the tailpipe right above some snow. The snow didn't get blackened. The engine is 3.1L V6.

Here's how it originally began: I was driving along, then braked. The braking felt soft. I looked at the dashboard and the CEL was on. That's also the same month when my mpg went bad. (I've been calculating it at every gas fillup.) The braking has not been soft again, since that one time.

If as Steve says it's not a constant leak anyway, could some third unknown factor have caused both the CEL and the lowered mpg?

Thanks for both replies.

The third reason could be a known unknown. Means something unrelated to the evap CEL is causing a drop in mileage. The CEL and lower mileage are pure coincidence. But that engine is idling fine, and has good OBDII indications when something is wrong.

Plug/wires are a possibility. Bad injectors don't have to throw a code. Or you changed gas, or have an overfilled trans or low tires. But my first guess is you're not measuring MPG correctly, or weren't before. That covers just some of the known unknowns.

The third reason could also be an unknown unknown. Of course we know nothing about that. It's all unknown.

Tom wrote in news:ia5fi5$rht$ snipped-for-privacy@speranza.aioe.org:

Your mileage problem is completely unrelated to that code. EVAP "leaks" are NOT the same as intake air "leaks".

EVAP codes are completely irrelevant to mileage and engine performance-- unless there's a deeper problem that is being misidentified by the computer as being an EVAP code. In those unlikely cases, it's usual to find a relevant TSB from the manufacturer.

Somebody needs to--among many other things--check your engine computer's various parameters, such as fuel trim, injector pulse width, and the several sensor values, before this issue can be resolved.

could mean you have a sticking brake caliper..

Mark

Tegger wrote in news:Xns9E1DD77EF8BCDtegger@208.90.168.18:

What are the odds here we're talking about a modified ROM?

...that could explain the bad mileage.

And the dense smoke from wheel well.