Hello to all!

Pretty basic question - is there a difference between the MAF sensor between the supercharged and N/A models of the X300? Or even the V12?

For context, mine is a ‘96 4.0L N/A X300, for the North American market. I’ve isolated that my issue (appears anyway!) to be the MAF sensor.

After skulking around online for awhile, I suspect I’m going to have to hunt around on eBay, so just confirming before I go further.

thanks

 

Yes ,

What is yours doing ?

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Thanks friend!

My idle is rough — it all started a couple weeks ago, when I stalled out in front of a traffic light. My idle began acting strangely then, but nothing significant. Now, I figured I needed to do a T/B cleaning, so I chalked it up to that. She fired back up no issue, and I was able to get her back home.

Then I cleaned out my T/B, and put it all back together. That’s when my heartaches began - my idle was rough and my throttle was sticking. In testing, I noticed my idle speed was anywhere between 950 and 1500 rpm. Previously, she was always bang on at 700 rpm, so it’s notably different. Additionally, I would press the accelerator, revving it up to 2500 or 3000, and remove my foot from the pedal. And the revs continued at 2500 or 3000 without my foot being there.

I have a separate T/B so I cleaned it and the idle valve piece out, and put that one on. While it made a difference, as the throttle doesn’t stick nearly as bad anymore (still does to a lesser degree), the idle is still too high.

As an experiment, I let it go into creep mode and see how fast she would go on a back road near my house — without my foot on the accelerator, the car managed to get up to 60 km/h (40 ish mph) just because it’s revs are up too high.

When I “blip” the throttle now, it can get stuck at around 1500 rpm, or drop down to 950 where it usually stays. But occasionally 1200 is where it ends up, and if it does drop to 700 it begins to hiccup, almost like it’s ready to stall out again.

I checked all of the engine coils, and thus far, their resistance test is good, and I haven’t been able to find any vacuum leaks…yet.

My thought is the MAF sensor and meter are most likely to be the prime suspects.

 

Fresh meat

The Mass air flow sensors are different for each SC , normally aspirated , and V - 12

When the MAF signal fails it will be seen as out of range by the ECU and the engine will regulate with less then optimum regulation missing this variable and a new set of data maps , so it will operate with the MAF connector off from reading others

When this switching acures it takes some time before going into default and when the signal is recovered some time to go back to normal

So your observations are good but a little background complication that can complicate you observations

Vee had a suggestion to give a slight twist in the pins / blades of the MAF connector

which is free and easy to .

From your history you may have started with an intermittent throttle position sensor ( or not )

In cleaning the TB you may have changed it's very sensitive idle position adjustment

In swapping the TB with a different TPS the idle position sensor value or null may have been different than your original TPS

So there is a ECU orientation to tell the ECU what is the new idle position or null

This was done with your original TPS at the factory to the original ECU

On paper the idle null value is 0.60 + or - 0.02 volts DC on the TPS return signal at the idle stop

The TPS will have a very very smooth increase as you very very slowly open the throttle toward but not to 5 volts , This will be starting at 13 % towards 100 % on a ELM - 327 device

The Mass air flow meter will read 1.2 volts DC at the correct idle and climb toward 5 volts at wide open throttle , this will be 4.5 grams / sec climbing toward 175 at wide open throttle on an ELM - 327 device

These 2 readings will be on the middle wire of the sensor's connectors that must remain connected

The TPS can be tested with engine not running with the key in the run position and hand twisting of the throttle butterfly

The MAF has a precaution to not rev the engine in the driveway as a TSB does not recommend running this way probably because of transmission cooling

Ask questions

 

The MAFs for the V12 are very different in that they are MAPs.

 

hahaaa good one — see, I don’t have much real world experience of the V12 so I wouldn’t know

nah, it’s just eBay has a huge array of used ones, and I want to make sure I don’t get the wrong one by mistake.

 

Thanks for this — I’ll get my multi-meter out this evening.

In my research on MAF sensors, I learned that a quick way to check if it functions correctly is to unplug the wire while the engine is running. Doing so should make the engine stall out.

This morning before work, I tried it, and my car hiccuped slightly, and then kept on running. If my research was correct, that would indicate a faulty MAF sensor.

 

Not all cars are the same

The Jaguar is special , it will keep running if the MAF is unplugged from reading

 

Go back to original TB, it has TPS sensor, matched to your car ECU, the new one wont, hence your RPMs can be all over the place as the TPS on that TB is set for another car and probably bordering between idle and non idle of your ECU. If it hangs clean it more, use fine sanding paper to clean off that yellow gunk if you need to. Whatever you do, make sure to not remove the TPS sensor without measuring its voltage first. Afterwards you can remove it and clean, you just need to be sure to install it in exactly the same position so it shows exactly the same voltage. When you get that sorted, you can replace your MAF with a new one, look for MAF for p38 range rover, ERR5595.
In most cases I don't think it's possible to diagnose Jag MAF without an oscilloscope, unless its completely broken and showing zeros on the OBD but that's also only on early cars as later cars will not start without a signal from the MAF. That said, failing MAF can cause symptoms like yours and rough idle, often wiggling the harness plus can temporarily bring it around. Also disconnecting MAF while the car runs should put on default map and the car should run ok and that may point to faulty MAF too.
One way or another getting live data from OBD should always be first step in diagnosing X300.

 

You can stick a pin on the back side of the of the MAF connector on the middle wire at proper idle and see 1.2 volts DC telling you it is alive at that point in time

Your idle value would be higher like 3 volts DC

On the TPS since the connector is underneath you can nick the insulation on the middle wire ( color X ) as it runs over the fuel rail

The valve cover is not a ground point as is insulated by plastic shouldered bushings

 

Indeed! Gotcha — alright, I’ll try that and report back.

 

Got it. I shall return with whatever my news is. Thank you, my friend.

 

Green / Yellow is the color of the middle wire of the TPS connector

Red 12 is the ECU connector

 

I'm not sure you ever got a clear answer. There is a different MAF for the supercharged AJ16 than the far more common normally aspirated one. They supercharged AJ16 engines use LNA1620AA. The normally aspirated one uses LHE1620AA.

You most likely need your throttle potentiometer sensor reset. If you had known the voltage, at idle, of the TPS, you could have reset it after you cleaned it.

Do you have a dealer or shop that has an old Jaguar PDU or WDS?

 

UPDATE:

As hinted at, the MAF is not my issue. Everything tested correctly.

So that leaves me at a quandary.

My T/B appears to be functioning correctly, and my sensors (when I tested of course) appear to be fine. Yet, it’s still giving me grief.

My symptoms as they stand now:

* high idle in Park and Neutral. Somewhere around the 1,500 RPM mark.
* high idle while in gear — the lowest it’ll go is 900 RPM, and when in Drive, it’ll be anywhere from the 900 to 2,000 RPM, regardless of inputs from me.
* acceleration without assistance from me — I can get up to 65 km/h (40 mph) without pressing the accelerator. Stopping the car is naturally harder as a result. In the “creeper” mode, it should always be in first gear — but it shifts up on me. I think at least go 3rd if not 4th.
* when in park at idle, there appears to be an occasional misfire moment. It starts up fine, then the hiccups begin.

There appear to be no vacuum leaks.

Any more ideas or chats you think I should check out?

 

Do you have a voltage value of the TPS at the idle stop and if the throttle naturally returns to idle stop ?

This value is very precise and requires a digital meter as the on paper limit is 0.60 + or - 0.02 volts DC

So you would be comparing agents a reading if you twisted by hand the throttle butterfly cable bellcrank .

There have been problems with the throttle return spring addressed by a stronger return spring in a TSB , there is a way around purchasing the stronger spring

 

You need a TPS reset. Read my post just before yours.

You can attempt the following: with the car hot, and in open loop, keep the car running, unplug the TPS and wait 10 seconds. Then plug it back in and see what happens.

Your only other alternative at that point is to loosen the bolts holding the TPS in place and see if you can adjust its position enough to get you to normal idle. Most likely, you'll need to remove the throttle body, take the TPS off, enlargen the holes into something closer to a slot, put everything back together, leaving the TPS bolts just loose enough to be able to adjust the TPS position by hand with a little bit of effort. Then once on the car, run the engine and adjust the position of the TPS. When it's at 700RPM, hot, tighten those bolts down. Ideally you should get a voltage reading on the TPS so you'll know what value your ECU is looking for.

Other than that, a TPS reset is what you need.

 

You can adjust the TPS with the TB still installed but takes a lot of patients and dexterity

The mount bolts are a torque bit of certain size

The original TPS sensor holes give little wiggle room and can be sized up with a drill bit to give you more adjustment

 

I believe you have two separate issues here. First, is obviously as Vee already said twice, you need a TPS reset as you basically lost the idle TPS voltage while you messed with your TB and now have no way to find out what it was. In ideal scenario you go to someone with a Jag IDS and they do an adaptation and all will be sorted. This isn't exactly easy these days as there might not be anyone around with correct hardware. The other is to try to manually adjust your TPS but before you do so I think you need to address your second issue first.

From what you're describing you still have a sticky TB and no TPS reset or adjustment will fix it so you need to get that sorted first. Your RPM depends on the TPS voltage(apart from extra air of course) so if you sometimes have 900RPM then 1500RPM it means that voltage changes, depending on how sticky it is or not in that moment.

First you need an OBD scanner, any cheapo will do, you just want it to monitor your TPS value. Even if the TB and TPS within it is set incorrectly which leads to high idle, it should still always return to the same voltage(between 0.52V and 0.70V) with the foot off the pedal and as close to 5V as possible with the foot through the firewall. If it doesn't and you sometimes get 0.6V and the next time you get 0.7V you will confirm that the TB sticks and you need to sort it out first. You do it in three steps:

1. First you remove the throttle cable from the TB so the cable doesn't pull on it and check the TPS voltage, with the car running, idle, and by moving the TB by HAND. If you get various voltages(that differ even by 0.02V when letting it go to idle) it means that TB still sticks or the spring that returns it to its resting position is too weak or the manual stop screw is screwed in too far.
2. Its possible that the TB springs(there are two) are a bit weak, after that many years, and you can either remove the bottom spring and replace it with the newer style spring from Jag(they are cheap) and/or wind it up an extra turn so you add extra tension to it, that should get the TB fully closed hopefully in its resting position. What I find while working on many of these TBs is that the bottom spring although useful is not as important as the top one, you can easily turn the top spring an extra turn and make the TB much stronger. It also helps if your throttle cable is a bit sticky(it does happen too).
3. Third step is again cleaning the TB inside, if it sticks you need to be absolutely sure that the TB butterfly is not catching on the TB across its length. You do it with the TB off the car and you set the stop screw where the TB butterfly to TB gap is 0.002" exactly, you check it with a spark plug gauge across its length and you clean it and adjust until that gap is there with minimal screw adjustment in. If the gap is not there, again use light sand paper, like 800 and sand down all the caked oily grime in there until you get that sorted and you're absolutely sure that the TB is set perfect as per factory spec.

At any point in this you can always check current TPS voltage with OBD scanner without starting the car. If you set it up on the bench to factory spec(0.002" gap) and then added extra turns to TB springs, you can then mount the TB to the engine, attach throttle cable and recheck your results with an OBD scanner, key in position 2 and foot off the pedal of course. Lets say idle TPS voltage with the foot off is now consistent 0.64V. You plug the MAF and the car should start ok, even without all the plastics. If it settles to normal idle RPM, lets say 850RPM, you're all good and fixed it and you can put everything back together and enjoy your car again.
If not, then you have two options, you try to find a dealer with the correct IDS so they can reset it for you OR you loosen the TPS screws and turn it to one side while observing the TPS voltage in OBD until it drops further to lets say 0.60V and try again. Despite how the TPS looks, there is enough adjustment in TPS holes and screws that hold it to TB to adjust it by 0.08V I think, which can be a difference between 850RPM idle and 2000RPM idle.
If you're lucky, adjusting it down by 0.02V or 0.04V should be enough to settle the RPMs to correct factory value and you secure the TPS again and enjoy your car. If you do get lucky make sure to remember that idle TPS voltage when ECU is happy and RPMs are correct. Whatever you do afterwards, that voltage value needs to be the same.
If you're however unlucky and your TPS is either faulty(voltage fluctuates without moving TB) or it needs more adjustment, you will need someone with IDS to reset it for you and/or replace your TPS.

Hope that makes some sense! Despite how it all sounds complicated, it is easy when you slowly and carefully go through the whole procedure! Let us know how you get on!

 

Well everyone here’s the long awaited update:

Scarlet roars again.

After more time and effort then I care to admit, I had to break down and bring her to my local Jaguar Land Rover dealer.

The dealer told me to bring it in on a Thursday at 8:30 AM. Later that day, they contacted me, asking for another day. The next day, they contacted me again, saying that they’d need to have her in until Tuesday the next week.

You can imagine my trepidation, expecting the bill to be massive with a simple “sorry sir, we are unable to diagnose your issue.”

But to my utter delight, I was wrong. They were able to diagnose and solve my issue, and only charged me for 1 hour’s labour. After a small amount of preamble the paperwork said:

“Removed throttle valve from vehicle and inspect throttle blade to housing gap with feeler gauge. Set to 0.02” as per specification. Checked and confirmed TPS, voltage output at closed plate correct with in spec at 0.61V. Performed TPS replacement/relearn routine with diagnostic equipment. Idle speed now correct.”

In essence, it was my Throttle Position Sensor in the end. I want to take this time to thank you guys so much for all your help with this, and you have my gratitude for all your help. You’re all so awesome.

I have to say, JLR treated me very well, and even gave me a couple hats too. Didn’t see that one coming. Their mechanic or technician I ended up speaking with asked me to consider calling him if ever I wanted to sell her. Not going to lie; that felt REALLY good.

Now I just got to scour eBay for the diagnostic equipment you guys have suggested to me.