Hi all, have just joined the forum having read some very useful posts on here. I've introduced myself in the introduction forum - My situation is that I have just acquired a nice and cheap 1995 X300 XJ6. Probably one of the cheapest with an MOT on it (so I wasn't expecting plain sailing!).

So, to describe the situation.....

The first extended drive I took it on, it drove perfectly for a good 50 miles. The first sign of an issue, I felt a sudden loss of power for less than a second but assumed it was a pot hole. Then it happened again and I noticed the CEL light came on at the same time but went out immediately (less than a second later). Gradually, the frequency of this increased such that it was happening more than once every mile. Every time it happened, the engine revs dropped for a split second, CEL flashed & engine then carried on running normally until next occurence. When stopped or crawling, the car would completely stall. Upon restarting, getting the car back into drive and moving again without stalling would become difficult. Essentially I'd have to keep the revs above idle when engaging drive (which I did not enjoy doing as puts extra stress on the drivetrain).

In summary, current condition:

• Car runs fine when cold (for up to 30 minutes) so will even run fine when coolant is up to temperature (have confirmed with an OBD scanner).
• Symptoms are only evident when engine is warm.
• Can happen at any engine load/rpm.
• CEL illuminates for less than a second (when the symptoms occur).
• When idling in Park/neutral or when in Drive but stopped/moving slowly, this results in a complete stall.
• Also, when in park, occasionally, if you rev the engine, it will only drop back to 1200rpm. Revving the engine lightly a second time, and the revs will drop back to normal idle speed.

So having done much reading through various forums, it seems that comparable issues have been experienced by other owners (not sure if exactly the same).

Based on the above facts, I need to look for one of the following:

• A bad electrical component/sensor in the intake / fuel system / engine / exhaust or a mechanical component that is not set correctly / dirty that
  • malfunctions only when warm.
  • or is permanently malfunctioning but will only result in no good engine running when warmed up.

What have I done so far?

Fluids

• Coolant - OK
• Engine Oil - Was a bit low (had to add 1.5L)
• Gearbox Oil - OK

Ignition System

• Spark plugs - Changed all spark plugs (Originals were Champions and looked completely fine. I have installed brand new NGK plugs)
• Coil packs
  • 2x coil packs had a single stripped bolt thread on the engine head. I found 2x new bolts with a good thread so all coil packs are properly secured.
  • Visual inspection - All coil packs look brand new with no damage to electrical contacts or rubber boot. I'm not sure how long it would take for them to visually deteriorate being sat under a cover.
  • Brand - No idea what brand they are as no markings or stickers on them.
  • Primary resistance - Confirmed primary resistance of 1.1 ohms on all 6 coil packs.
  • Function test - I disconnected each coil pack 1 at a time with the engine running. This produced a change in engine tone for each coil pack so can assume they are all functioning.
• Battery
  • Voltage reading of 12.13V (so a bit low but shouldn't affect the engine when running as utilising alternator @ ~14V)
• Crank Position Sensor
  • Haven't disconnected or tested but i'd assume a malfunctioning CPS would also make it difficult to start.

Air Intake

• Filter Box - OK
• MAF
  • This is a 'Lucas 20 AM' unit with a manufacturing date of '23 96' - I'm assuming this means 1996. The car is a 1995 model so either it was replaced within a year or more likely someone has replaced with a salvage part at some point.
  • Cleaned electrical terminals
  • Inspected wire - Looks OK
  • Have checked function with OBD reader - air flow rate appears to react in good correlation to throttle position so I think the MAF sensor is ok.
• Intake elbow
  • Removed and cleaned (including temperature sensor)
  • Breather hose that sits in top of the elbow had a small amount of oily liquid in it that has dripped into the elbow (but sounds like this is normal)
• Throttle body
  • Visual inspection of butterfly valve - appears to be clean with no build up visible when looking through open valve.
  • Cables - The throttle body has 2x pulleys. Looks like the lower cable goes to the accelerator pedal. The upper cable I have no idea what it is for, but it looks slightly loose.

Fuel System

• Injectors
  • Confirmed resistance across all injector terminals at 15.7-15.8 ohms.
  • Have added a dose of Redex to the fuel tank in case the injectors are slightly dirty.

OBD Confirmation

• I have monitored the car using my OBD reader but have not picked up any fault codes or noticed any particularly suspect readings (I understand OBD was very primitive back in 1995 hence why there's probably not much information).
• Short term fuel trim - Sits within +/- 10% range
• MAF - Sits at 0.04 - 0.05g/sec when idling (4 - 5g/sec)
• Throttle Position - Around 11% when idling and ~85% when pedal fully pressed
• Coolant Temperature - Stabilises at ~80C

Next Steps/thoughts:

• Throttle Position Sensor - Currently, based on what I've read, this is highest on the list of likely causes. How can I test as the OBD reader appeared to show it reacting as expected.
• Throttle body - Remove & clean + adjust sensors/cables - How to do?
• Vacuum leak? - how to check?
• MAF could still be faulty (despite the above)
• Coil Packs could still be faulty? - Carry out a visual spark test (look for blue spark).
• Fuel Filter - I've bought a replacement but haven't installed yet
• Fuel - Fully drain fuel tank & refill
• Dodgy O2 sensors/cracked exhaust?

Apologies for the wordy post, but would appreciate some input so I focus my efforts in the right area.

Thanks!

 

Hi Simon

Welcome, and congratulations on the new motor. You will have great fun with it.

Based on your symptoms and the testing you have done, I don't think there's many of your "Next Steps" that I would see as likely causes (maybe Coil Packs).

Your assumption about the Crank Sensor unfortunately is not right. The Crank Sensor has many failure modes and what you describe is one of them. It's hard to test it unless you have a scope so replacement is the only option (If you do have a scope I can provide a good waveform for comparison). If a new sensorit doesn't fix the issue, it's only a matter of time before you will need it anyway, so just keep it in the boot for when you do.

A less common failure point is the ECM controlled relay. It can cause your symptoms. It's at the front right under the bonnet. Try swapping with another similar relay to see if there's a change.




Another possibility is the fuel pump. Again, hard to test as there is no pressure port on fuel lines on the X300. You need to rig up your own (there's some threads on the forum somewhere on how to do that).


Others will have more suggestions, but TBH unless you're dealing with a known good Crank Sensor you could be testing stuff for weeks.

 

Agree with Brendan, change that sensor first...........

 

Hello, thank you for taking the time to reply, it is very much appreciated.

I have ordered a new crank sensor which unfortunately is on a bit of a long lead time.

In the mean time, I will remove the current sensor/connector this evening and clean it up as much as possible to see if this makes an improvement.

Will let you know how it goes.

 

Entirely agree with what has been said already. I am wondering whether the high idle speed comment you made might suggest a parallel problem with the throttle position sensor or the throttle body needing cleaned, also common problems on the X300. I would leave for now till you have the crank position sensor replaced, as it is more or less the mandatory first step on these cars.
If you are stuck for bedtime reading in the interim, check out the various / numerous threads about throttle position sensors and throttle bodies, and you will soon get the picture.

 

I had an issue some time ago where the engine would "miss" occasionally. I changed the crank position sensor which solved the problem. Then I noticed that some of the wire insulation on the removed sensor had been worn away! Worth checking that you do not have an intermittant short! Alec G.

 

Thanks for the consensus. Fingers crossed for when the part arrives.

On a separate note:

1 - Should the engine bay on these have a plastic under tray as mine doesn’t have anything

2 - On the AC crank belt and a couple of areas next to it, there is a thin layer of copper/brass coloured residue. Any idea where this is from?

 

There is no undertray on the X300 other than a small piece just behind the front bumper. FYI, you can check out all parts for the X300 here

https://parts.jaguarlandroverclassic.../brand/jaguar/



Can't really see what you are referring to as residue in the photos. But dare I suggest rust? or maybe copper grease that PO put on to stop a squeal?

 

Things you will want, or need to address, soon to eliminate issues going forward.

1. Remove the throttle body and clean it out. (you only need to remove 4-10mm bolts. There is no gasket at the air intake, even though it looks like there should be. Watch out for the small coolant hose that connects into the bottom of the throttle body, I use a golf tee to plug it temporarily)

2. Replace the coil packs. Buy only Diamond branded, made in Japan coils, or the QYL brand sold on Amazon.

3. Replace the oxygen sensors. All four of them.

you do not have an EGR Sensor, so that one stays off the list. Getting ahead of these parts will clear up symptoms going forward, should you have any. TPS replacement is too costly for me to recommend without a problem first, but is probably also inevitable.

 

I think you're right about the copper grease theory as it's all on the belt.

So the throttle position sensor finally arrived and unfortunately the car is still cutting out temporarily/stalling when warm.

Tomorrow I will remove and clean up the throttle body and TPS if I can get to it.

Regarding the throttle body, I do have a secondary issue where if I rev the car, sometimes the revs won't drop back to idle but instead hold at around 1200rpm. Tapping the pedal again seems to drop the revs back to idle.

I have traced the problem back to the cables on the top of the throttle body. There are 2x cables. The lower cable I have confirmed is the accelerator pedal cable. The upper cable I'm assuming is related to a sensor as I have noticed it doesn't always fully retract when releasing the throttle. I have confirmed that holding this cable in the out position when releasing the throttle does indeed cause the revs to remain high. Can someone confirm where this cable goes as it seems to disappear into a cable guide in the bulkhead and also what would be causing it to not retract correctly? Is there a spring at the other end of it somewhere?

 

I hope you don't mean that Crank Position Sensor?

Did you try the ECM controlled relay swap?



There is a known issue with Throttle Return Spring being weak and causing exactly what you describe. There was a TSB about it and there is a hack to fix it also. I've attached a PDF. I think this was written by @aholbro1 but he was too modest to put his name to it. Give it a try, it's free to do.

 

I meant crank position sensor you’re right!

Ive had a look at what you sent and it’s different to what I see. I’m referring to the cable circled in my photo:

 

I don't know what that cable is TBH, I don't have it. Is your car a 3.2L Engine?

I can only guess that it's a kick-down cable . I know the gearbox on the 3.2 is different and more mechanical than the electronic box on the 4.0. But I don't know if kick-down is mechanical. Hopefully someone who knows more about the 3.2 set-up can answer.


The spring mod is the same though. The spring is under the swivel plate that the cables attach to, on the left side of you photo. Remove the 3 torx screws that you can see in the picture.

 

Brendan,

Your memory is excellent, as usual. The 3.2L cars used the ZF 4HP22 hydro-mechanical transmissions. We didn't get the 3.2L engines in the U.S., but our 3.6L XJ40s used the same transmission. The kickdown cable connects the transmission to the throttle valve cam as in Simon's photo.

There is also a kickdown switch under the accelerator pedal, but I don't recall what it does. It may inhibit the A/C compressor clutch under WOT.

Cheers,

Don

 

Once you have completed this, please report back. This is most likely the source of the sticky throttle.

It's four 10mm bolts. Be careful of the small coolant hoses running in and out of the underside of the throttle body. I use golf tees to plug them up temporarily. Even thought it seems like there should be a gasket between the throttle body and the intake, there isn't.

 

Hi Brendan, yes it is the 3.2L AJ16 engine. If it is a kick down cable, I'm confused as to why when it sticks it would prevent the engine rpm returning to idle when you rev the car with the gearbox left in park?

I have confirmed it does this by manually revving the throttle and holding this cable in the pulled out position. Despite the throttle itself closing, the rpm still remains elevated. Is there a possibility this could have something to do with the idle air control valve or completely separate?

So I have today removed the throttle body and made a few observations (probably unrelated) to my issues:

1 - The top right bolt on the throttle body appears to be stripped so there are only 3x bolts holding it to the intake manifold. Seems to be very secure even with just the 3x bolts so I don't think a problem.

2 - The throttle position sensor connector is slightly damaged (but not sufficiently so to prevent it from clipping in)

3 - Rather foolishly, I tried to remove the idle air control valve from the throttle body. Unfortunately, one of the bolts has sheared - it appears to be completely seized with threadlock. Any recommendations for how to remove (bearing in mind I don't have a workshop and only standard hand tools). Or is my best option to buy another throttle body off ebay?




4 - The idle air control valve is a bit dirty but probably not a concern. Is there a way I can confirm it works correctly with a multimeter or visually/by hand?



5 - The throttle body appears to be very clean (Judging by the threadlock, stripped threads, damaged connector, I'm assuming it has been cleaned very recently.)




6 - The throttle position sensor is marked with the 'Ford' logo - I assume this is normal as Jaguar was under Ford ownership at the time. I've tested the resistance across it using a multimeter and it does seem to be working in that the resistance does vary as you rotate it. Not sure what the correct resistance values are for this though?



7 - For the second time, I have managed to snap the crank breather hose?? connection off the intake elbow. Will try and glue it back on again, not sure how critical the crank breather hose connection is



If I were to take the car to a garage, would their equipment be able to interrogate my ECU any better than my OBD scanner (bearing in mind OBD functionality seems very limited on these early cars).

Just a hunch but I can't see anything wrong with the throttle body/sensors that would be causing my problems.

So at the moment I need to get the bolt removed or a new throttle body so that I can reassemble.

I would like to reconfirm the ECM relay as there is a chance that both the air con and ECM relay are no good. I'm assuming these can be found on ebay...

Thanks again for all the help, as always, it's appreciated.

 

Simon,
The topic of whether the throttle position sensor is a Ford item or not has been the subject of debate for some time, with no conclusive outcome. My own sense of the matter is that it will be a Ford part, and that the Ford item would be a much cheaper replacement than the Jaguar item, but this is a topic on which reasonable men seem to differ. The various threads on the subject of TPS / high idle chronicle the debate at length, but for the present purpose, it is worth noting that the original TPS does not have the Ford (or Jaguar or any other) logo on it, although it does bear a strong physical resemblance to the item in your picture. Further evidence I suspect, that you are not the first person to be working on your throttle body. As to whether the non oem TPS is the cause of your high idle, it is difficult to say, but there is an adaptation procedure to "tell" the ECU what position the TPS is at, and it might be worth reading up on that in the related threads too. Suffice to say, the path you are on is a very well trodden one (right down to the sheared IACV screw!) and does lead to a happy ending with patience.

 

The OEM TPS was stamped with a FORD logo. I've seen this on both of my 96 XJS parts. If you purchase a new one, from Jaguar, it will not have that logo anymore, but I'm not convinced the TPS is at fault for anything. There are no aftermarket, or alternate TPS options. This part is expensive, is known to go bad, even though it tests well, and is known to cause mysterious problems, but let's not go down that path just yet, you have too many other more likely issues to address.

The stripped bolt at the throttle body would be a concern of mine, especially since there is no gasket between the throttle body and the intake. You really should get that fixed. You can helicoil it, or use a time-sert, which is my preferred thread repair product. If your throttle body was allowing air to get sucked in through this corner of the connection, then it could lead to idle issues.

The broken elbow should be replaced. If air is sneaking past the repair, then it will lead to idle issues as well.

Both of these situations create the probability of unmetered air entering the engine, so the MAF is telling the ECU that its reading a certain amount, but then those two areas could be allowing more air to sneak through. Let's fix those up.

To get that screw out, you will need to get at dremel, or some kind of saw to put a notch in it so that you can use a flathead screwdriver to drive it out. BUT FIRST HEAT UP THE PART. Do it in this order, 1. create the notch and make sure your screwdriver gets a good grip on it 2. heat up the metal, probably best to use a propane torch, or maybe a soldering iron, then when hot the threadlock will let go and 3. use the screwdriver to get the rest of the screw out. Or you can simply drill it out and use a helicoil of timesert to fix it, tapping a larger hole probably wont work here. You will need a new IACV gasket, and there is probably a o-ring that is missing. No need for a new throttle body. If you don't have a dremel, it's worth the investment. I use the wireless battery powered one. You'll wonder how you completed some tasks without it.

I think that's all I got.

 

Thanks both, I will try and get that screw out as a start point like you say and hopefully also source a replacement elbow from ebay. Would another option be to stick the throttle body in the oven (with the TPS and IACV removed of course)?

Regarding the throttle body, would using a small amount of gasket sealant be an acceptable solution in the area around the stripped thread?

I've had a good luck under the car this evening and made some more findings:

1 - No undertray

2 - The lower radiator is looking extremely unloved! Is this the oil cooler?

3 - There is an electrical connector hanging down below the washer tank. Any idea what this connector is for?

 

I drove an XJS, so while I’m very familiar with the engine, not entirely familiar with things unique to the x300, like that hanging electrical connector.

That unloved mess does indeed look like the oil cooler. It is not needed in the XJS and many people, including myself, removed it, permanently. It removes a common source of leaking oil. I’d research a little bit and find out if you can do the same for the XJ6. If so, I can recommend the replacement o-rings and bypass fitting you’ll need to complete the job.