Need some help if possible with a 2001 Manual Jaguar S Type 3.0, 90K
Symptoms

Quite Severe Hesitation/Stumble under load. Occasionally smooths out
No Codes pending or stored

Already Done

MAF sensor is new and verified operational with Scan tool

No physical signs of vacuum leak and normal Short and Long Fuel trim, so no indication of extra compensatory fuel

TPS opening percentage from my Live Stream seems constant enough. Idle is around 15-16% and max at 80%. Holds percentage OK, does not drop off. I have not done a Voltage test, just my scan tool that shows opening percentage.

Car starts immediately cold or hot and idles smoothly but occasionally I feel a miss at idle, hot or cold.

IAT sensor is fine based on my scan stream

I have sprayed Carb cleaner around intake manifold and Air intake with no rev change

I have done the easy three plugs and new coils but not the others yet.

When I disconnect the MAF, idle quality is terrible but active driving performance is perfect on closed loop. No hesitation

If it was a bad coil or plug, why would it drive perfectly without MAF.

I am rambling but honestly stumped. I know that I should take the manifold off and do the other plugs and coils but that doesn't seem to make sense. If I had a bad miss or injector block, I should be too lean on one bank and my Fuel trim should be high.


Should I take it to Jag and be done with it. I hate to do that!!

Any ideas? Thanks in advance.

 

You can't expect to see physical signs of an air leak on that engine without taking it apart. The most likely - very common with age, see all the threads - is deep down. When it flexes you get a momentary leak you may well not see and the engine stumbles. You can't spray anywhere near it if the manifold etc are still on!

Failing that, there are other hoses, valves, etc. And the cats. But the hoses "everyone" has reported so many times are by far the most likely.

Easiest is read a few relevant threads using Search and do what everyone else did.

 

Well, it doesn't have to make sense... The RH plugs and coils may not be your culprit, but I'd change them anyway. If the plugs are supposedly good for 100k miles, you're almost there. The threshold to set some DTCs is very high. You could be skirting right under that limit. Plugs are normal wear and tear items (coils, too, to some extent) so I don't feel bad suggesting them, even if you report back they were no help.

Also replace the IMT O-rings. Get the genuine OEM seals. Cheap insurance against vacuum leaks.

If you're sure there are no other vacuum leaks, try a pair of upstream O2 sensors. Once again, these are normal wear and tear items, and a VERY important part of the control system. When you disconnected the MAF and tricked the control system in open loop, the O2 sensors readings are ignored, so that might explain your results. As they age, O2 sensors become less responsive but they have to get really bad before the PCM will fault them. Keep in mind new upstream O2 sensors are my preferred fix for everything after a recent positive experience, but I think they are well worth the gamble in this case.

 

Agree with the plugs and O2 sensors.

Both ours had almost the same issues. The Black one worse. NO codes, even the dealer was scratching, coz that engine was running sooooo bad.

Bit the bulllet, 6 plugs, 6 coils, inlet gaskets, upper and lower, PCV elbow, PCV adaptor at the rear of the LH clylinder head, O2 sensors (upstream).

This car had the plugs replaced just before we got it, adn yes teh plugs were newish.

The coils were also newish looking.

The inlet gaskets, well, what a mess. Being the earlier engine, it has the "biscuit" style gaskets, with the seals imbedded in the plastic cage. There were bits of "seals" missing, so a vac leak. We all sprayed all sorts of inflammable stuff around this engine to NO avail.

The elbow in the depths was NEW, whoopee.

The adaptor on the stand pipe at the rear of the LH cylinder head was SAD.

O2 sensors, no idea, just swapped them out coz I had them.

RUNS SWEET.

What actually was the problem 100%, no idea, but those missing bits of inlet seals are certainly very high on the list.

The Silver car was different, and I tested my theory of the elbow my way. I removed the pipe from the throttle body that feeds the adaptor at the LH rear pipe, and capped the vac spigot at the throttle body. The engine ran SWEET, no misfiring, no hesitation, so that elbow is the culprit.

I have the new one on the bench, some "Santa type" might fit it for me one day, I can always dream. In the meantime it runs without that system and is just fine.

My very unscientific diagnosis is from all the years I have had with the V12's, and good old common sense, good dose of old age when basics rulled supreme. Clearly it still works, coz all that fancy stuff still showed both engines were FINE, HAHA.

 

On 3.0 plugs due at each 70K / 7yrs.

Can't see it being coils and I'd not spend the money for what may be worse ones unless you buy quite expensive ones from a reputable supplier.

 

I think it varies with markets.

Down here its 100K Kms or 7 years.

NGK, state 100k kms, no time frame.

NGK also state the O2 sensors at the same time as the Iridium plugs, which makes that a very expensive service for all 4, or even the 2 upstream units.

I found some CAD brand coils for ours, and at $38 each, I was happy, and 2 years on all OK.

I do realise there are some absolute rubbish out there.

 

OP is in Devon (*). We use miles. 70K miles.

Miles.

3.0 plugs were platinum; 4.2 iridium. I expect 3.0 with iridium probably OK but cost more.

Does the 2001 even have IMT / IMT o-rings to change? I thought not...

(*) just about could be Oz?

 

The car manufacturer's schedule always overrides the supplier's suggestions. In any case, a calendar limit on the plug or any ignition component makes no sense.

 

Agreed. Something to keep in mind is the context. If a vehicle is running well, a specified life limit is a maximum guideline for service life. Replacement is then preventative maintenance, before the component starts acting up.

If a vehicle is not running well, those guidelines go out the window. Since we are talking plugs, they can fail well before then. (The fault could even be an external issue such as oil fouling or preignition damage.) Sounds rather obvious, but I've had many people tell me the plugs or whatever can't be at fault because they are good for (insert big even number here) miles.

FWIW.

Am still leaning towards the upstream O2 sensors on this one. They fix everything, including dirty ashtrays and sticking window regulators.

 

How about fuel economy, have you noticed any difference, using more fuel??


At that sort of mileage I'd suspect the lambda 02 sensors as a possible cause, if you intend to keep the car I'd consider replacing them anyway, but by all means check first
Good luck

 

I know its Devon, and we once had Britsh Miles, just saying.

Platinum are being replaced bt Iridium down here. Right or wrong, thats what NGK are doing. My Iridium were $17 (thats Australian $$) each, not that bad, even for a grumpy old Aussie.

IMT, yes, done both my cars in the very early days.