Took the Jag out on a 20 mile round trip, after a few shorter trips without issue. Long story short, I ended up stranded when the problem persisted and the car eventually refused to maintain idle and kept stalling out. First ~20 miles were perfect, then problem starts infrequently, increasing in frequency until it was happening every 1-2 seconds. Had it towed to my mechanic where it sits this weekend waiting to be looked at Monday.

Here are two charts I pulled capturing the issue while it occurred. The first shows about 30 minutes of normal operation, then the problem shows up:



The second shows about 30 seconds of running at idle while the problem is ocurring, which ended in a stall. I did not touch the throttle during this recording:



I have CSV data for both of these I will be sharing with my mechanic.

 

I noticed that the Mass Air Flow has a value of 0.0 when the RPM's of both snapshoots are running at the white markers . On paper 7 months ago I calculated the mass air flow rate at 5500 RPM at 250 grams for a 4.0 litter engine . Not able to confirm with the ELM327 for my software key dropped out . Green / Pink wire of the mass air flow sensor connector should read 1.2 volts at idle . The Pink / Slate wire should be a ground through the ECU . The Black / Green wire is the reference voltage from the ECU of a value not given on the Jaguar wiring breakout sheet . This Black / Green wire splices and powers many other items . All 6 fuel injectors , canister close valve ( not present on latter X300's ) , EVAP control valve ,and the EGR valve . This wire is so important that it appears to be supplied by 2 different and tied together reference voltage regulators in the ECU . Sensor part # LNA1620AA ( Lucas 70401B ) is for XJR LHE1620AA ( Lucas 70390B ) is for everything else 3.2 or 4.0 (I'm not talking about V12) per member AL NZ . They can't be swapped between the 2 different ones for the data map in the ECU will not calculate the fuel injector pulse length correctly . I believe they can be sourced from Land Rovers . You can look for damaged wires before you were the change the MAF . Your occurrence appears to be heat related by electrical current flow through the device or working environment ( except for the canister close valve ) an could be caused by any of the listed devises shorting the power or signal to case ground . Tapping on them while reading with a needle meter ( or engine response ) may show something before being hit with a mechanic's bill .

I'm not saying this is the spot of interest but is my observation from the information presented . I can be wrong for I can be 2 tacos short of a Mexican platter at times .

The other perimeters in the graph may not have been " scaled "so they are showing a flat line on the live data graph . The engine coolant reading stayed steady and correct and didn't bip at the time of the occurrence , this changes the short term fuel trim . The RPM should be more like the second snap shoot and not the first . The fuel ratio should be around 14.7 ( related to the STFT of 0.0 or Lamba of 1.0 )

This reply will change as I edit

 

Thank you, I posted in a rush, and didn't think about how the scaling would make it look.

Here's a scaled/zoomed section from the first graph that better shows everything. I noticed the "Absolute Throttle Position" seems to wig out and shoot up, and doesn't match the other throttle reading. As you can see from this one, the MAF was reading at one point:



Here's a scaled/zoomed snap from the "idle/stall" chart that shows no reading from the MAF. Also notable is the throttle position on this one zooms up, but at no time during this recording did I touch the throttle:

 

There's the bunny . Have you cleaned up and secured the TPS connector at the bottom of the butterfly ? The TPS wiring is tied into the EGR Valve and fuel tank pressure sesor . Independent of the MAF wiring run . If you can duplicate the occurrence at idle you should see 0.60 volts on the TPS . Try tapping on the EGR valve and FTPS . I noticed the difference in the throttle PID's . By removing the EGR valve and FTPS connector you may remove the fault on the TPS but you may get a CEL code for EGR and fuel system .

 

Update: I dropped the car off at my go-to mechanic 3 weeks ago (when I last posted.) Long story short, he did nothing. So I picked it up yesterday and went at it myself.

The TPS was visibly covered in grime and gunk on the outside, but didn't look too bad in the connections. I disconnected and shot a good amount of electrical contact cleaner in both sides of the connection. After letting it dry and reconnecting, I took it out for a drive. 5 miles down the road, the problem comes back, so I head home.

I ran it in my driveway while jiggling and tapping on the EGR and TPS connection, and could not get it to duplicate the problem; the problem persists, but there is no specific reaction to the tapping/jiggling.

I'm still at a loss. I would love to have a concrete diagnosis before spending more $$$, instead of still guessing weeks and weeks later.

Would a complete removal and clean of the throttle body make more of a difference? I did spray the connections without removing it, I just had to get a few wires and hoses out of the way.

Could this be coils going bad, and the throttle readings are a red herring? I have ordered a set of six of the cheap ($75 for 6) Chinese coils made by QYL. I plan to throw those in and see if it goes away for a couple weeks before spending $600 on SNG Barratt coils only to have the problem persist.

 

I installed the QYL coils about 2 months ago and so far so good.

 

Thanks, that's good to know. Popular wisdom says that the cheap coils fail within 6-12 months, but if I can get the problem to go away for 2 months straight, at least I'll know its the coils.

I love this car, and I've got no problem sinking another $600 in, but not if it doesn't solve my problem.

 

Today I removed the throttle body for a thorough cleaning.

This is what I was able to see when I just peeked in from above before removing it:



I thought, not too bad, right?

This is what it looked like once I removed it and could get a good look:



And this is the backside:



Most importantly, this is what the TPS looked like. Bear in mind this is after I cleaned it in situ by spraying contact cleaner from a few inches away:





So, now everything is squeaky-clean and re-installed. I took it on a short one-mile trip, and throttle response is tangibly improved and idle feels smoother. Most importantly, my live charts taken from the OBD reader are showing both Absolute and Manifold throttle positions working together correctly.

One mile isn't much, but I feel pretty good about this. Only time will tell if the problem persists. For what its worth, I have not changed the coils out, because I want to try one fix at a time to isolate the problem.

 

Coils are not likely to cause this problem. You would get a misfire, not a shutdown.

If this solves your problem, then congratulations. It was a cheap fix! Your pictures are an excellent illustration on why removing the throttle body is the only way to get it clean.

Keep us posted.

 

Update: No joy to be found.

Took the jag on a longer drive yesterday, and the problem returned after about 5 miles. Same symptoms, tach dropping sharply, everything cutting out for a second, then surging back to life. If it happens at low enough idle it always causes a stall.

I was able to limp it back home to the driveway about five miles, dodging traffic and stalling and restarting at every light and intersection. I was unable to capture chart data, because I forgot to turn it on initially, and once the problem starts the OBD cuts out every time the tach drops. When its happening every few seconds, I can't get the bluetooth to connect to the reader fast enough to start recording before it cuts out again.

Not really sure where to go from here.

 

The orange wire . This wire carries a data bus around to the different nodes of the cars digital multiplex system . This data bus is what you are reading and since it drops out of your ELM327 connection it may be corrupted somewhere and not meet it's protocol . This wire also runs to the column movement module .

 

I want it to be the easy answer- the TPS. On this car, it really is responsible for all kinds of havoc.

if you can get your hands on a used one, it might be worth your while...

 

I agree, I'd like the easy answer, or any definite answer at all at this point.

I've considered finding a used one to swap in, but I fear the manual adjustment process or the cost of going to a dealer.

 

Thanks, that may explain the cut out of power to the OBD connection when it occurs, but surely this wire cannot be responsible for the engine cutting out, can it?

 

To avoid that, take a voltage reading from your TPS at idle. It should read 0.6v, but could be different if someone else had replaced/altered it and had the TPS Reset using Jag software. Whatever that reading is, you should match if replacing the TPS. That's all there is to it.

The car just wants to know what the base voltage is when the car is at idle. If you match it by adjusting the position of the TPS, you should be fine.

The problem you are having does fit in the realm of a failing TPS. I wouldn't necessarily gamble $400 on a replacement, but a used one...hell yeah, I'd jump on that.

 

Hello everyone,

Interesting reading and suggestions there.

I had a similar issue with my 96 XJ6 and there were 2 main issues:
One injector was intermitantly faulty: I checked the resistivity between the 2 pins and found out that one of them (N°1) was out of the scope.
Then the MAFS had good voltage readings. At first I assumed it was not at fault but I ended up changing it with a cheap used one from the UK (50€ delivered I believe) and it solved the problem !

I know you changed yours but did you try to clean it with some specific products ? If yes, that might be a cause of failure. I know they are very fragile and sensitives to K&N air filters oil for instance.

Good luck with the troubleshouting

 

Since the last trip that ended in a stall, I haven't been able to start it again. The fuel pump relay was not clicking on, so I suspected a dead fuel pump, which if it has been dying may have caused my intermittent stalling problems.

I replaced the fuel pump, which was a long and dirty job. The fuel pump installed was the original (at 150,000+ miles).

With the new pump installed the fuel pump relay rapidly clicks on and off, and the car will crank but not start.

FWIW, I also replaced all the ignition coils just because I had them. I have not been able to get it to turn over since doing that, so I don't know if they're good or not. The ones I pulled out were el cheapo Chinese ebay replacements installed by the previous owner.

 

With the fuel pump relay you're looking for the 3rd click back to on ( from the crankshaft sensor ) . Since you have the first 2 ( sometimes ) that charge / prime the fuel rail the control circuit is intact ( sometimes ) coming out of the engine ECU . You must have relay click for power to the pump . If you want to hotwire the fuel pump to stay on at all times you can put power into the relay socket that goes straight to the pump taking the control out of the picture so you can focus on a running engine's regulation . Take a blade connector with some heavy gauge wire from the forward most slot in the relay socket to the battery positive or the relay box terminal post positive . Use the clip as a switch so you don't arc the relay socket . Will be hot at all times so don't forget to remove the clip on shutdown .

From a earlier reply concerning TPS if you want to read it with a meter : you can do this through the gas pedal and meter in the seat

The X300 TPS is 3 wire and can be read with a meter with the engine off at the ECU connector as you move the TPS through it's range .

Wire GY is Red 12

GB is Black 7

UW is Red 11

X300 N/A and S/C is the same.

Look for a bip or spike to high on a needle meter as resistance as you sweep it through , my not be able to see with a digital meter .

####### RESULTS #######

With the connectors on the ECU and the key to on position the ECU reads 0.601 volts at idle .

Paper clip into Red 11 to Red 12

Idle = X ohms

Full Throttle = Y ohms

 

This is the exactly the same issue I have with mine see my post..ive not found the cause yet.

 

I have been following this thread for a while now. I was hoping for an update or resolution...