: Mass air flow sensor Help please



grayrock
08-23-07, 11:04 PM
Hello to everyone.
I'm fairly new here, so if I've posted this in the wrong forum, please let me know nicely.
I have a 2003 Deville 4.6L and I have been having a problem with it. I think I've narrowed it down to the mass air flow sensor. But not sure. What is happening is that it runs rough after warming up. I checked the codes and it's lean on cyl 1 and 2. I've changed the fuel filter. Put in a new air filter. Checked for vacuum leaks. Replaced the gas cap. And from reading posts here, I think it might be the MAF sensor. When I unplug the MAF sensor, the car runs great. But when I plug it back in, it runs real rough. I didn't run it long because I do not know what all the MAF sensor affects, but that is why I'm thinking it's the MAF sensor.
Any input?
Thanks everyone! Great site you all have here. :thumbsup:
Thomas

codewize
08-23-07, 11:39 PM
Ok let's start by saying the car should almost not run at all with the MAF disconnected. The MAF tells the computer how much air is flowing through the plenum so it can dump the correct amount of fuel to the injectors. Without the MAF the car shouldn't even really run.

That's a pretty crude description but that's the basics of operation.

How many miles are on the car? Is the airbox the factory set up? If the MAF were the problem I would expect a different code but I could be wrong. The elements in the MAF may be contaminated but again I would expect different codes. Additionally I don't think the MAF ever really goes bad unless it's been played with and damaged.

Have you looked at the MAF itself.

AJxtcman
08-24-07, 06:48 AM
http://www.cadillacforums.com/forums/northstar-performance-technical-discussion/113253-p0171-p0174-codes-intake-leak.html

FrankT
08-24-07, 06:54 AM
Codewise is on the right track, if it was a MAF Sensor performance issue I would also suspect another code P0101, but it has to be oustide of a calibrated range to set P0101, if the MAF is just on the threshold, then I would say maybe it could set a lean or rich code. Before replacing an expensive part like the MAF remove it and gently clean the MAF Sensor elements. While the MAF is off the car inspect throttle plate and throttle bore for excessive coking and carbon deposits.

Due to the lean codes that you do have, inspect the rubber duct plumn piece between the intake and throttle body for leaks. Do this before removing the MAF and with the engine running and listen for vacuum leaks. you can also use brake clean or carb spray around the intake and injector seals to help find the air leak, but be carful, the stuff is flamable.

Your problem is related to both banks so check those common areas.
Good Luck FrankT

ewill3rd
08-24-07, 07:24 AM
I replace so few MAF sensors that I rarely ever suspect them unless I am working on a Catera.
You didn't mention the trouble codes you have, but it does sound like a P0171 and P0174.
That indicates you are getting unmetered air, which means something is leaking.
Look into the threads pointed out above.

When the MAF is disconnected the computer relies on other sensors for data, such as the MAP sensor, TP, and O2 sensors to gather data on airflow. The computer is programmed with fuel control tables based on these readings and will run differently. Just because it is better doesn't mean the MAF is the problem.

If you gave us more detail we could help more, but based on what I see, you probably have a plenum leak.

AJxtcman
08-24-07, 07:50 AM
I bet I have seen 100 plenums leaking. I am not saying I have repaired all of them. We have about 10 Techs. That would be about 3 Plenums a year per Tech for the last 3.5 years. I see a lot of Plenums fail after Cross over Gaskets have been replaced. I bet 80% have had the cross over resealed.

grayrock
08-24-07, 08:48 AM
Ok. Here is a little more information:
The car has 108,000 miles.
The codes that were stored are:
DDM U1713
PCM P0102
P0171
P0174
P0741
IRC U1016

Thanks again everyone. I think I might just have to take the car in and get it checked out.
Tom

ewill3rd
08-24-07, 09:54 AM
I'd say you have a split plenum. Did you click that link above and look at the other topic?

The P0102 is because the computer sees incorrect airflow based on calculated values.
It is related to your leak.

I think that other topic I put some information on a little self diagnosis, all you need is a can of choke cleaner or brake clean.

grayrock
09-02-07, 10:04 AM
Thank you for the information. It is the Plenum.
Do you know where I could get the parts from? Is it dealer parts only?
Thank you!
Thomas

codewize
09-02-07, 10:14 AM
Cool, glad we could help. Some of these guys are pretty darn smart. Give the boy some rep points :)


Thank you for the information. It is the Plenum.
Do you know where I could get the parts from? Is it dealer parts only?
Thank you!
Thomas

Ranger
09-02-07, 01:12 PM
Thank you for the information. It is the Plenum.
Do you know where I could get the parts from? Is it dealer parts only?
Thank you!
Thomas
http://www.gmotors.com

grayrock
09-05-07, 02:10 PM
Thank you to all who responded.
I have the Plenum, bought it from a local chevy dealer for $29. Now just waiting for the intake seals to come in (should be today or tomorrow) and then I'm ready to get into this. :)
Thank you again.
Tom
:cool: