So my car was running like crap for several weeks. Getting terrible gas mileage and shooting black smoke out the tailpipe on start up and hard acceleration. I replaced the O2 sensor and now am getting 14 mpg instead of 10, but Im still lacking the gas mileage and performance I remember getting when I bought the car. So where do I start looking for a problem. Is it maybe the temperature sensor or MAF?

 

Have you ever sprayed the MAF hotwire? That usually works wonders for gas mileage.

 

14 mpg city is actually on the good side of normal for an S4, it's what I get. If you record 20 mpg highway, it is running right.

-Sean

 

But, uh, how would I spray this MAF stuff? Is it easy to describe where to spray? I have workshop manuals, but it is not obvious to a newbie.

-Sean

 

You're running very rich on the mix. Could be MAF signal, could be the computer not sending the correct pulse to the injectors......either way, you've got too much fuel in the cylinders, (or an air restriction somewhere, (but the O2 sensor should figure that out)). Sorry, not my area of knowledge yet.
Not much help I know.

 

Normally the MAF on most cars can be removed from the intake plumbing, or just one side exposed, and you should be able to simply spray the cleaner into the body, though you may not be able to actually see the wire. Just give it several good shots and let it dry out (which takes no time at all).

 

MAF cleaner works pretty good if it's just crap in the unit.
I'd remove the MAF and spray it down on the bench though.
I did mine on the intake refresh, and you've got to be very careful not to mess with the actual wire. They're fragile.

 

I will buy some cleaner. I am getting 14mpg on freeway driving. It also is idling funny. I think it is due to the richness of the fuel to air. I have cleaned the idle stabilizer so that's not a factor.

 

May want to have a look at your fuel pressure damper and regulators, too. A bad one will allow fuel to be sucked into the intake and can cause some wild rumbling at idle, and maybe even foul your mixture causing it to go rich.

 

If one of the diaphrams is torn, you should pull fuel into your mityvac when you hook it up.

you can access those and the maf my removing the airbox.

To remove the MAF have a 1/4" drive 8mm deep socket on a universal and a 12" extension and a pick-it magnet. You can feed it in from the side, use the magnet to position the socket on the hose clamp. It's a ton easier than trying to get your hands in there.

 

Hmm, this is something I would expect that my shop guys do when they change the air filter and do general maintenance, they are really good about doing the little extras to keep her going good. I will check with them. My mileage is pretty well up to spec since I changed the O2 sensor, and they checked all that stuff at that time as well.

 

We've lost 3 MAF's here cleaning them with spray.

If you suspect yours is weak, send it for review and calibration / rebuild.

I just had one rebuilt by a rennlister and its fantastic now.

 

Are they fragile because of age?

 

How do you ruin an MAF with the cleaner? Making me hesitant to give it a shot.My car is my daily driver so I cant have it going down.

 

I don't know. I think maybe the spray solvent had an unintended interaction with an insulator in the electrical connections that support the platinum wire.

I've got 3 cars running mafs and will never use maf spray.

Jadz is the one who grenaded the mafs, two of his and one of CPayne's. They were all originals. Not sure what he sprayed them with, I think it was a typical off the shelf spray. I bought one of the cars from Jim and had first to source another maf.

Don't do yours. Send it to Rich Andrade or Louis Ott/Speake. The platinum wires degrade, a certain internal circuit can fail, and they generally need calibration. In fact, Roger probably stocks mafs with a core charge.

No offense, but Maleficio has never even seen a 928 maf. His is afm.