MAP or MAF sensor

[tezles42]

I have recently had the MAP sensor replaced on the S type 2.5 (58k) due to a slight surging in revs when traveling around 50 mph at 1500 ish rpm. The fault code at the garage, they said ,pointed to the MAP sensor. It was ok for a month after the alleged replacement but the fault has returned. I have been informed that the more likely issue is the MAF sensor. My fear is if it was the MAP sensor, was it ever replaced or has it faulted again, which seems unlikely. Can anyone assist in pointing me to where the MAP sensor is. I would like to check if possible for signs of a new part. I have found the MAF sensor and that clearly has not been touched. What does each do and are they related. Has anyone else out there had the same symptons with their car.
Many thanks in anticipation.
Carl

[J44EAG]

Hello Carl,

MAF =Mass Air Flow sensor. The symptoms you describe can be caused by a duff sensor or one that may be covered in black treacle like crank case breather residue. The unit senses mass air flow and also I believe the air temperature via the hot wire in the unit.

Find the air filter box and follow the tube to the Air Flow Meter. This is a cylindrical unit joined to the air filter box by a short length of rubber tube. The next unit along is the MAF sensor. It is a square shaped plate secured into the next section of trunking by Torx screws. If you remove the multiplug by tweaking the stainless clip away from the plug, you can then pull the plug off the sensor. Then remove the Torx screws and the MAF can be lifted out of the trunking.

You will find a down stand with a delicate hot wire and possibly a bulb like unit. Do NOT touch the hot wire with any implement. If it is filthy, use spray switch cleaner to remove the black residue. That will some times cure the fault you describe. If the unit is faulty, obtain a new part and refit. Replace the Torx screws and reconnect the plug.

You will normally find a blob of paint on each screw which gives some indication that the unit has been previously removed if paint on a screw or on the MAF has been broken or the paint marks do not line up screw to sensor wise.

It is also worth removing the trunking back to the metal throttle body. Having removed the trunking, you will see inside the throttle body and perhaps more black grunge around the throttle throat and the brass circular throttle plate. If the oil build up is great then it can affect idle speed quality. Clean with carburettor cleaner, soft rag and a very soft tooth brush. Do not mark the very soft coating on the throttle throat. Check also that the part load crank case breather pipes to the trunking are also clean.

Regrettably, keeping these items clear of oily sludge often gets missed when a car is garage serviced. I clean these parts every 10k miles which makes the car more reliable.

Mike

[tezles42]

Many thanks, Mike i will go and have a look. What is the MAP sensor then and where is it. This is what the garage said they replaced but i have my doubts given the symptons returning so soon.
Carl

[J44EAG]

I`ve looked in the good book for MAP sensor but nothing listed. Mike

[tezles42]

Mike I have just been informed its a Manifold Absolute Presure sensor and its location is at the back of the manifold and is a pig to see let alone get to. For what its worth i will try a clean of the MAF sensor and your other sugestion. If no change i will try a second hand MAF switch. Seems to be plenty around second hand.

[J44EAG]

There is a MAF on eBay at the moment. £40. Uncertain what the new price would be.

Eurojag are good for second hand parts at the right prices. Worth a call to them to see if they can help. Neville Anderson at North East Jaguar Spares was breaking a V6 recently so he may also be able to help.

Probably quickest and easiest to remove the manifold to change the MAP sensor if that is what is needed. Worth changing the two small rubber air pipe elbows at the same time. They crush and split with age and don`t cost much to replace. If the V6 manifold has to come off, gaskets will have to be changed. Might as well do the plugs at the same time as one bank is impossible to do without manifold removal. One thing just leads to another!

Let us know how you get on.

Mike

[tezles42]

Looks like it will keep me busy for an hour or two then.
Cheers
Carl

[tezles42]

I managed to get a MAF sensor on ebay as new for £40 which is half the dealer price. The old one was in a state to say the least. I was speaking to a motor technician at work regrding the MAF. To say its a little non descript would be best, but this thing can change the way your car is running, its smoothness on accelertion, cruising, Cruise control and gear changing. All by sending the message to the cars brain on what it needs to do in the current driving conditions. This is all done through the wire and bulb within the sensor, amazing. Whats even more satisfying is that i didnt realise how roppy my car was running. It had obviously got worse over time hence only now realising somethings not quite right. What a difference now. Best £40 quid spent in a long time. Now looking for a rear parking sensor module.

[J44EAG]

Well done, Carl.

The MAF is a part that is critical to the overall electronic architecture. Just like the throttle body, the throttle pedal, the airflow meter, temperature sensor and Lamda sensors, if any one of them go out of limits, then problems begin.

Often the MAF can be cleaned but when that fails to do the trick, then replacement either new or good second hand is the only option.

I think I should cover this subject on our Forum page in our magazine sometime and use the basis of what has been posted on this thread as the scenario. A useful addition to the knowledge pool. This is the second time I`ve heard of a MAF playing up during the past couple of months and both you and the other member who made contact describe the same symptoms.

Your mechanic chap is certainly correct of what MAF failure causes when it gives up. I`d add that keeping the unit clean is half the battle. Letting sludge build up on the hot wire cannot do its life expectancy much good in the long term. The unit is incredibly delicate and I suspect that sludge might eventually cause the unit to overheat or short out.

For those who are wondering just what a MAF looks like, here are a couple of images taken straight off the internet. The Jaguar unit we have described in this thread is not dissimilar in appearance.

MAF image 1.jpg

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MAF image 2.jpg

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Glad you got fixed up Carl, and thanks for your input.

Re the parking module, this is located in the spare wheel well on the left had side and is frequently drowned with rain water together with the rear fuse box if the boot seal fails. Simple answer, check the boot seal and drill a small hole at the lowest point in the wheel well to let any standing water out! Replace a defective module with EXACTLY the same part number that you remove from the car. There are several different types of module on various S-types and fitment or the wrong one can ruin your day. Suggest if we wish to discuss this subject further, we open a new topic in the Electrical Section to avoid this thread going off course.

Mike