FYI: Tried to chase out idle issues in 1995 X300 with 110K on the odometer:
- new crankshaft position sensor
- new throttle position sensor and throttle body adjustment
- new coolant temperature sensor (the one that ECU uses for adjusting the mixture)
- new intake air temp. sensor
- new idle air control valve
- new spark plugs
- welded exhaust manifold cracks
- replaced plugged catalytic converters
- new oxygen sensors
- new coils from Eurospare

The car ran fine for a month, then started misfiring which got progressively worse, until the idle issues returned.

Returned the Eurospare coils, replaced them with proper coils. SNG Barratt has correct coils for ~ $500 for six of them. They are Made in Japan by Diamond, they are the same coils that Jaguar installed at the factory.

The idle issues are gone. I don't remember this car ever running as nicely as it is now.

I suspect that X300 does multiple ignition pulses per coil at idle. It's common in large displacement engines that idle at low RPM (650-700 IIRC). This means that the coil needs to fire more times per minute at idle than say at 1500 RPM. Which in turn explains why the car runs like **** at idle and stumbles if you floor it, but cruises just fine at 2000 - 2500 RPM. I might hook up a scope when I have more time, just to satisfy my curiosity.

P.S. If you are in Boston, Samules Jaguar is the best shop, IMHO. They are both cheaper and better than the others in my experience. If not for them, the car would probably end up as parts.

 

I suppose you've seen and read this thread?

https://www.jaguarforums.com/forum/x...0-coils-93966/


For a while "Eurospare" was selling the correct (Diamond Manufacturing) coils.

It takes research to determine what you're actually buying these days. Everybody, it seems, is in on the "label engineering" game. And the term "OEM" has become meaningless.

Cheers
DD

 

For Info - We still have good stock of the Diamond Electrics ignition coils. Glad to hear they have worked out for those that have made the extra investment.

Jaguar XJ6 XJR XJS Ignition Coil LHE1510AB Made in Japan True | eBay

 

Worked out great, thanks!

To me it's not about the 'extra investment'. The other option turned out to be a complete waste of money. It also tuned out to be a huge time drain and a source of a fair amount of frustration. The fact that the other coils are cheaper is no consolation when the car is not drivable

The irony is that the previous owner also a problem with coils, and he replaced them with cheap aftermarket ones. Then he spent an awfully long time chasing out idle issues. Eventually he got so frustrated that he gave up and sold the car.