I first posted 2 months ago, bought an 84’ XJS with 82K miles, not running, sat for many years. Engine oil was very clean, wiring untouched, tires 80%, clear title and no plates. Got it to start and idle for a few moments, enough to convince me it was worth the price. $1300. Had it hauled home, had it running off and on enough to tell the ECU had issues. Installed the ECU from my other 84’ that I just had Roger Bywater refurbish (Roger’s Super Enhanced Version), started the car and it just purred (with some roughness due to very very old spark plugs, old plug wires and a badly worn throttle position sensor.
Tried the Oregon DEQ station test, failed first and second idle slightly. Installed new: spark plugs, wires, distributor cap. Drove freeway 5 minutes to DEQ station, held idle at 1500 rpm in waiting line when I was second in line, manually held idle to 900 rpm with gas pedal during test, and passed! (of course unplugged the two wire connector in the trunk for the test.
Also, followed another guys idea on JLF and modified a 94 Ford Mustang TPS to fit where the Jag TPS belongs, and made it read 0.32 V at throttle stop position.