My wife is complaining that her 2006 XK8 is not running quite as well as it was when we purchased it six weeks ago. She's put a little over 2,000 miles on the car with the odometer currently reading 38,360 miles....

So I pulled the air filter. It was squeaky clean....

Then I pulled the Mass Air Flow sensor. It looks grimy to me, but there are no codes or warning lights on the dash. So I decided to pull the MAF sensor from our 2005 S-Type (coming up on 70,000 miles) for comparison - it was sparkling clean and I've never had to clean it. Then I decided to pull the MAF sensor from our 2004 Lexus RX330 (coming up on 121,000 miles) for additional comparison - it was every bit as clean as the S-Type's MAF sensor and I've yet to have to clean it, either. All three of these MAF sensors are Denso. The only difference I can see among them is that the XK8 and Lexus MAF sensors are secured by two Phillips screws while the S-Type MAF sensor is secured by two Torx screws....

I'll get some MAF sensor cleaner and carefully clean up the XK8's MAF sensor. Perhaps that will restore the car to the running condition it was in when we purchased it (although I believe this issue to be subjective perception on my wife's part although I must admit that because I rarely drive the car, I have nothing to compare here)....

But that still leaves an important question - what are the potential causes for the XK8's MAF sensor to get so grimy after less than 40,000 miles?

 

Cleaning the MAF should be part of routine servicing which is probably why your other cars are clean.

 

Is there a K&N filter in the XK?

 

landmannn,

I do all of the routine maintenance on all of our vehicles and always have. I have not needed to clean any of the MAF sensors in any of our current vehicles until seeing the grimy condition of the XK8's MAF sensor this afternoon....



avt007,

All of our vehicles run their stock air filters. I am unwilling to risk the potential sensor issues caused by K&N air filters....

 

I know people will argue with me here, but what grade of gas is she putting in the car? On my car, it makes a huge difference.

Try a can of BG-44k in the next tank, I do it religously on an annual basis, as preventative injector fouling.


You could also hook up a code reader and look at the fuel trims at idle and at 2500 rpm, see if the short term stays in the 4-7% range, and your long term isn't above 10%

 

The car is currently getting premium gas at fill-up time. She's tried two or three fill-ups with regular gas, but she realizes now that the XK8's 4.2 needs premium. Our S-Type 3.0 has always run just fine on regular. She assumed the XK8 would as well. Lesson learned....

I poured a 20-ounce bottle of Chevron Techron into the gas tank yesterday afternoon. I expect the Techron to help just as the BG-44 would - I know from prior experience that Techron is good stuff. I also plan to clean the MAF sensor once I pick up the appropriate cleaner from Advance Auto Parts in the next day or two....

Thanks for the feedback....

 

After a full tank of premium, a bottle of Techron, and a thorough cleaning of the MAF sensor, my wife reports that her XK8 is now running better than ever....

I went ahead and took the time yesterday to clean all four of our vehicles' MAF sensors. My 1999 Dodge Ram pickup is also running better than ever as a result. Haven't driven the 2005 S-Type or 2004 Lexus RX330 since the sensors were cleaned so no report on them yet....

Moral of the story - clean your MAF sensor on a regular basis. I'm going to start visually inspecting them every 10,000 miles or so....

 

 

I'm glad the better fuel and a quick addition of a fuel additive product worked for you. Decreased performance and fuel mileage isn't worth the 10-15 cents per gallon difference in my experience.

 

No good explanation of the difference. It helps to know how things work to diagnose ...the wire in the MAF is heated by a set voltage and the air passing it cools the wire, changing its resistance, which the electronics can measure and adjust mixture based on air mass according to an algorithm. If you have one MAF that is cruddy compared to others under controlled conditions, the perception would be that that dirty MAF wire is running at lower temps than the others and not keeping the wire clean due to heat.

 

Meant to mention that Bosch MAF's have a cleaning cycle that runs the hot wire up to 1000 deg C. for 1 sec after engine shutdown to keep it clean. It is possible that your dirty one was not self cleaning properly or this is not built into that particular Denso sensor.

 

We've owned our XK8 for only six weeks and a bit over 2,000 miles. So I'm going to assume that its grimy MAF sensor was due to cheap gas by the previous owner. It's an easy 60-second process to remove it and take a look at the element, so I plan to make that a part of every oil & filter change I do to this vehicle. If it begins to look grimy again, it will be cleaned. I may just go ahead and spray it even if it looks clean simply because I have it in my hand and a couple of sprays of MAF sensor cleaner can't hurt....

 

Just a small point that I would like to make. Since the gas does not come in cantact with the MAF, only air, what effect should the octane of the gas have on the condition of the MAF?

2000 XK8 1995 XJ6

 

I do not know. I began this thread by asking what could be causing our XK8's MAF sensor to appear grimy. The car's air filter element is clean. No one has truly answered my question. But the MAF sensor is now clean, the car runs much better, and it is both easy and inexpensive to clean the sensor. So cleaning it is now a part of my oil & filter change routine....

 

Ok, how can gas effect the MAF?

OP, if the car has been driven in wet weather, that will do it. Water will go through the filter and onto the MAF carrying dirt.

 

The XK8 is now my wife's daily driver. It has seen rain, in fact plenty of it during the past couple of weeks. And the pollen is now beginning to get thick around here as well. As I said, I'll make cleaning the MAF sensor a part of the typical routine maintenance for this car. Never had to do that before....

 

Most sports cars have the air intake in a place were they can suck in air with as little turbulance as possible, other cars put it where ever is convenient. Which means sports cars suck in wet dirty air in rain, the C4 vettes were terrible about sucking water in, as they are bottom feeders aka air intake is about 4 inches off the ground.

 

thought I didn't quote the OP, I was addressing the part about Being a new purchase, and new owner/driver (coupled to the female pursuasion) I took a stab at the lower grade gas as an obvious potential cause.

Oil gets sucked into the air pipe in the older gen cars through those part and full load breathers, cleaning the MAF is more important I belive on those earlier 4.0s than our 4.2s though.

 

You can have a perfectly clean air filter and a dirty MAF if there is air bypassing the air filter. This can happen if the gasket is not fully seated.

 

No he is not, K&N's will let dirt in and if you put to much oil on them. Just go ahead and buy a new MAF.