Should I part out my X300 because of lack of available parts?

I’ve gotten 255k out of my X300. I’m now a little tired of the time consuming effort of tracking down an intermittent stall problem at low speed pulling away. I described the problem here

I’m going to take the throttle body apart and clean it AGAIN and test the TPS, and also change the fuel filter and test the fuel pressure.

But my concern is the lack of availability of a reliable replacement if the sensor is bad. Unlike the 308 there does not appear to be a rebuild service.Similar issue with MAF sensor.

I hate to do it but my time is now more limited and I need to focus it on my XJS and my '94 XJ40 (which has been infinitely more reliable and also has 270k - no poor OBD2 lack of code generation perhaps, but needs a cylinder head gasket replaced).

Yesterday I cleaned TPS, MAF, AIT and tested a new CTS. Drove the car 30 miles. Flawless. Cruise, all gears, sport mode, stop/start on steep inclines …everything. Nothing. No transmission warning lamp.

This morning I warmed it up and it started to stall in the driveway.

My other concern is that I can find many posts describing this behavior but I cannot find a single post that results in a solution. Perhaps it’s a bad wire buried in a harness.

I’m not one for quitting but this is really becoming too time consuming. SNG offering 99 pct of the car is 1 percent short.

Is it time to part out valuable reliable parts and scrap the rest?

Are you saying JLM12074 is not available? I’ve bought one in last couple years.`JLM12074`

BTW, if you live anywhere near New Hampshire USA, I do have a Jaguar PDU which will pick up live data from every wire coming out of the ECU. You can see exactly what’s going on when it happens.

You don’t say which year your car is, but on some early cars there was a clip on the wiring harness that could lead to intermittent problems.

Its funny, 255,000 miles…
A series 3 or older , you were happy to get 50,000 miles before it all came apart. The xj40 faired a bit better , The car is old and served its purpose…
Your call to move on, but it goes to show the x300 was a great, great car.

John: As you have bought one can you tell me the correct way to test the TPS Sensor? Thanks for pointing out sourcing. I’d like to definitively determine that it’s the TPS that is bad. I believe I would go with SNG rather than one that’s out of the bag on Ebay with no returns accepted…even from what looks like a reliable seller.

All - my model is 1997 X300. Above I meant I have cleaned the connectors on those sensors. I’m about to remove the throttle body.

Unfortunately I live in SC but you’re the first person I’ve heard of who has a PDU and knows how to use it.

Pete: My car is a 1997 and does not have the clip - but I’ll verify.

Joey: Of course you are correct. The miles are 99.9999% highway and these drive trains are so solid the car should be good for 500k with periodic maintenance. I have done about everything to this car from complete suspension overhaul, diff change, starter motor (aagh), front spring drop, engine mounts, rear hub rebuilds…This particular problem is frustrating because of the lack of certainty over what seems to be a very repeated problem. The Jag CD of course on the X300 is also very poor which does not help.

I’d like to keep the car for its periodic trips to the golf course. Hopefully I can PROVE it’s the TPS…if I can get the correct testing procedure.

One additional question - I’ve seen conflicting information on this forum about the need to re-train a new TPS. What is the correct answer to that question?

I found the TPS test procedure on the XJ40. If the voltage is meant to smoothly change when applying throttle then perhaps I can back probe the wires to check the voltage signal using a Power Probe (after deliberatey shorting out the Power Probe of course to avoid accidentally applying 12 volts to the ECM!!), without having to remove the throttle body? I need to look at the electrical diagram.

Hi- Since you are in South Carolina, I suggest you join the Coventry Foundation which is out of Columbia SC. They have a PDU too.

If you want to do it on the bench, you need one of those voltage supply units off eBay that can generate exactly 5v. Maybe something like this: 30V/60V /10A 5A Lab Adjustable DC Power Supply Line Variable Digital Voltage LED | eBay

On the input wire you supply 5v. With the throttle closed and the TPS rotated correctly, you should get .32 to .34 out with 5v in. This is “close enough”. Your ECU is too smart for its own good and could have learned a different v value is “idle” but .32 to .34 is fine. It’ll relearn eventually. The PDU makes the ECU learn immediately.

Btw testing for intermittent problems is futile! Throw parts at it :slight_smile:

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John - Dang - I totally forgot about JCNA. Thanks for that link and also the link to the DC volt Generator. I’ve thought about getting one of those just for EGR system testing on my old F150!! - Like me everything I have is OLD.

I did realize I had the X300 Electrical Repair Manual. Duh!
Black/Green - Ground
Blue/White Reference Voltage 5V
Green/Yellow Sensor Feedback - It says 0.6v at idle and 4.9 at full throttle but I take note of your numbers.

I’m going to remove the Air intake and MAF piping and see if I can get my P Probe on the wires.

I’d heard that the PDU is hard to use. Are you saying you can loan one and learn how to use it without a Masters? Also does the same unit work on a 1992 V12 XJS and a 1994 XJ40?

While the issue is intermittent - one day it’s there the next it is not, it does seem to remain for the trip - even when the ignition is turned off and on. If I go and start it and then immediately get the issue in my driveway I’m thinking there’s a chance I might see the problem when I test for it. Could be wishful thinking.

If the manual says .6 then it’s .6!

The PDU isn’t hard to use, it’s all menu driven. You’d probably look for a menu option called engine set up. At least that’s what I needed for an XJS to do the TPS. The unit does work with XJS, XJ40, even late series 3 XJ12, but the adapters vary greatly. Some time you plug in OBD2 port, but on the 92 XJS it’s a brown socket under the shifter console. Then on the same car if you want to log the ECU you need a giant adapter/patch box with 30ish pins that goes between the ECU and ECU plug.

I don’t know if they would let you borrow the PDU or make you use it there. While PDU does stand for portable diagnostic unit, The portable part is a lie. There is a 6 foot long sheet metal console that you bolt to the wall. The Portable part has to be put on the base station to load after menu selections.

Understood. It looks like the Coventry Foundation points to JCNA on tools. I’ll talk with Dick Maury about them. I’m not close to a JCNA group.

As others have said, the age of the car might have dry or frey wires.
Does anyone make new harnesses?

I carefully back probed the reference voltage and it is 5 volts. Checking the sensor voltage at idle I get a consistent .78 volts. Turning the throttle slowly I seem to get a smooth increase in voltage. I only revved it up to 2 volts but I had no OBD connected to see the RPMs. I did think I saw a moment when the voltage quickly went down to 0.3 and back but it happened so quickly. I’ve rested the car and I’m going to go back out and see what I get. I’ll leave the back probes in for now as its parked. I ordered a male and female pigtail from Ballenger to enable easier testing and eliminate the back probing. I can always use the connectors for something else later. I’m hoping if there is something sporadic going on I will see a voltage drop.

Here’s 35 seconds of OBD data recording with the car in the driveway but fully warmed up. Take a look at the Absolute Throttle Position Readings when the RPM changes. There’s a lag (real or ECM or software) but also does 15.69% open at idle and 29.8% at 3,168 rpm seem right? I would have thought at 3,168 it would be much higher. Also note the fluctuating idle readings from 633 to 740. I did have some issues a year or 2 ago and changed the Idle Air Valve - Stepper Motor!

I think the next step is to remove all the air and the TB and make sure everything is clean. The harness looks good with no visible issues.

My X300 (XJR/6) ownership…6-7 years as a daily driver…was confirmation that durability and reliability are two different things…and “trouble free” ownership is yet a third.

I sold the car at 171k miles and am sure the engine and trans would’ve last much much longer. And the car was built like a tank. It was never gonna start falling apart. So, it was very durable.

And, in all those years and miles it was totally reliable. It always started, drove, and delivered me to and from my destination, whether near or far. Never once was I stranded by the roadside or on the back of a tow truck.

But…trouble free? Not hardly ! I called it “The Tormentor”. :slight_smile: My list of repairs was as long as your arm.

Gawd, what a great car to drive, though !


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Doug - my experience with the X300 has been similar. My experience with the XJ40 was infinitely better.

I have updated a thread I opened earlier with regard to the hesitation/stalling issue which I believe I have resolved. You can read it HERE.

II will update that thread if the hesitation manifest itself again. Separately I will be checking my TPS with an analog meter when I get a replacement for my dead one.

As always thanks to all for support!

John - I did speak with Dick Maury and am going to be contacting the Coventry Foundation. I may be able to drive the car to Columbia and try the PDU out.