Bad gas mileage at ilde?

On my 93 525, I wasnt positive on which way the cluster needle for the gas mileage is suppose to go. But it seems as though I get horrible mileage at idle. It goes to the 0 side instead of the 40 side. Is this correct? im averaging between 15.9 and 17.4mpg with almost all hiway. The exhaust has an odd smell sometimes like I have never smelled before. Not coolant, rotten eggy or a rich smell. Its smells chemically kinda. Ive been working on cars for 20+ years and have never smelled anything like it.

The valve from the brake booster to the intake has a nipple on the underside that is broken and sucks air into itself. Is it suppose to be plugged or is it suppose to take air into it? Is there a hose that is laying out of site that has broken off of it?

Miles per gallon...if you're not moving at idle it will be 0, coasting at idle it will go the other way...come on now

I believe rotten eggs mean a dead cat

Maybe someone can help with the booster...probably should have a line connected

lol Thats what I kinda figured. But my audi is the opposite and a 325ix Im working on goes to the 40mpg side at idle. Not a rotten egg smell...

If the car is not moving, you are getting 0 mpg. The gauge is working correctly

First thing I would do is repair the vacuum leak at the booster. Then before I condemed the cat convertor I would be looking at an O2 sensor. Before that I would be looking at tune up items like plugs, wires, injectors.

Your milage seems a little low for an M50 525. Could be a lot of things, heavy foot, auto trans, even a small amount of stop and go mixed in, or what you city folk consider highway driving sometimes

My 535/5 averages about 24, mostly highway, but I run it hard too, everytime it goes out.

We really need a whole lot more info to be much help.

If it smells like a fire-cracker...that's the combination of nitric oxide and nitrogen dioxide (NOx). It's from running near or too lean. Any significant vacuum leaks or deficient fuel delivery would definitely be suspect.

Originally Posted by S406

On my 93 525, I wasnt positive on which way the cluster needle for the gas mileage is suppose to go. But it seems as though I get horrible mileage at idle. It goes to the 0 side instead of the 40 side. Is this correct? im averaging between 15.9 and 17.4mpg with almost all hiway. The exhaust has an odd smell sometimes like I have never smelled before. Not coolant, rotten eggy or a rich smell. Its smells chemically kinda. Ive been working on cars for 20+ years and have never smelled anything like it.

The valve from the brake booster to the intake has a nipple on the underside that is broken and sucks air into itself. Is it suppose to be plugged or is it suppose to take air into it? Is there a hose that is laying out of site that has broken off of it?

Have you tried pulling the error codes via the stomp test ?

Does the broken part pull air all the time? If so fix it.

If you do the O2 sensor, spend the $15-$20 and go ahead and swap out the Coolant Temperature sensor as well. The CTS is what was causing mine to cough at idle (sometimes die) and have worse gas mileage. I was back up to 25-26 hiway on my 91 525 before it got wrecked last night with the CTS change. In prior weeks I fixed many vacuum leaks and cleaned the ICV which helped but didn't cure it.