Findings:

- Given the age of the X300 cars, ignition coils will likely cause you grief. In my case all stock coils were all failing at 109K, the plastic case was cracked. Some brand new aftermarket ignition coils fail intermittently, and only after being subjected to 20-40 minutes of heat. The car ran fine while cold and shortly after a warm-up. My idle problems started after coils have been heat-soaked for 20-40 minutes. Nothing quite like the engine stalling on a freeway off-ramp leaving you without power steering and without power brakes. Get good ignition coils from a reputable vendor! Don't go cheap, consider them a safety issue.

- The cheap ignition coils are crap, and a pain to troubleshoot. To add insult to injury, the Jaguar ECU's ability to detect ignition coil failure leaves much to be desired. Jaguar uses 2-wire coils that are crappy by design. As a side note, the 4-wire are much better unless they are made by in Germany for Porsche/VAG/BMW. If they are, they are even crappier than 2-wire Jaguar coils.

- If you want to troubleshoot coils, have someone who can hook up an oscilloscope and look at them. Apparently a trained eye can tell both a misfire and a bad coil by looking at the signal.

- Leaking valve cover gaskets are not conducive to ignition coil health. Replace them!

- Install the oil separator kit for the crankcase ventilation, if it's not there. There was a TSB for that. Bathing the throttle position sensor in oil will not make it any healthier. The TPS is stupid expensive ($250-ish) and when it goes south the computer needs to learn a new one. Not a DIY job unless you have requisite tools (VCM+IDS or equivalent).

- The chip in the ECU and the EGR valve need to match. There was a TSB for updating the EGR and the ECU chip. Make sure that they are compatible/of the same vintage, otherwise the car will either idle like crap or tend to die at idle/low RPM.

- Bad Intake air temperature sensor can cause idle problems, without throwing a code or illuminating "check engine" light.

- Don't trust the diagnostic capability in your Jag's ECU, especially if it's a '95. It's not good.

- Be careful where you take your car. Some so-called "Jaguar specialists" in the greater Boston area don't know squat about X300 and would not be able to repair anything non-trivial if their life depended on it. The only shop that was actually able to diagnose and repair my car is called "Samuels Jaguar", located in Boston. Elston Samuels knows these cars extremely well His prices are also very reasonable, more so than some of the "specialists" that proved themselves to be utterly worthless.

 

Another endorsement for Elston from me. My Jag only goes to his shop.

 

"As a side note, the 4-wire are much better unless they are made by in Germany for Porsche/VAG/BMW. If they are, they are even crappier than 2-wire Jaguar coils"

that did make me chuckle, but so, so true!

I'm dreading the day my 4 year old comes home from school to do the 'growing the cress on a bit of damp tissue' experiment...all that extra humidity in the local area will see Beemers misfiring and stuttering like Porky Pig

 

Excellent summary.

Specific info on the R493 EGR & Throttle Spring Recall:

https://www.jaguarforums.com/forum/x...recall-126057/

 

I just got my car back from Elston and Bob at Samuels for them to fix the same issue, and after cleaning out the intake tract and throttle body and adjusting the throttle spring, it now drives like a normal car. No more idling at 2500 RPM in traffic. Everyone needs a shop like Samuels in their life.