What does the mechanic mean when he says a code is "lean running condition"


#1

I own a 1996 Mazda Protégé with 128,000 miles. I had it in for a check of a sewing machine sound. The mechanic tested it and found, among things, a “lean running condition”.

What does that mean?

(I also have more questions that follow in other posts)


#2

It means that the air/fuel mixture ratio has more air in it than it should for the correct mixture. The opposite of that is a rich mixture, or too much fuel in the mixture. A common way a lean condition can occur is when a air leak happens in the intake or exhaust passages.


#3

If the car idles roughly and sometimes stalls while idling look for a leak in the rubber air intake.


#4

Can you post the actual code? It should be on your copy of the shop order.
Under what specific conditions does the engine make the “sewing machine sound”?


#5

The car does not stall while idling but when idling, sounds noisy if in gear and if in neutral, is quieter. No code was posted on the shop order. I have not tested out when the sewing machine sound occurs. I will do that today when I am out and about doing errands. I am making a list of followup questions for my mechanic and will include this one.

How does a lean running condition affect mileage? fuel emissions? safety? Mileage seems to be ok.
Thankyou!