I changed the spark plugs over the weekend (using same Champion RC12YC) for the 1996 AJ16 powered XJS. Rough idle with the 32 second power dip is back.

WTF?

I guess I have to take it back to the Jag Shop and get the computer to fix the idle...

ugh.

I double checked the connections, the coil springs, I unplugged each coil, and it was noticeably worse as I unplugged each coil. All plugs are dry...I don't know why this car hates getting it's plugs changed.

Wondering if I should swap in different plugs? Maybe the NGK BKR5E?

 

Switched plugs to NGK BKr5E...no change.

I can't understand how I could have created this problem with a spark plug change.

 

Sorry to hear that Vee,
Is there any chance that in changing the plugs you have disturbed something else? Have you checked individual plug HT leads (may be a partial break in one lead or faulty insulation - try running it at night to see if you can see any arcing), HT connections to distributor cap, low tension leads etc.?
Good luck,
LeeP

 

Might have cracked a plug wire internally of casing. Ohm test leads and replace that one or all.

 

None of those things mentioned would explain the 32 second cycle.
Luck, RagJag

 

I'm going to guess my car is staying in closed loop...

 

Apparently my intake manifold gasket is leaking...at least that's what the shop just called to tell me.

 

If you have a problem every time you take the coils out, then the problem must be with the coil wiring. I can't find any other explanation.

 

That's the solution I was circling before I took it to the shop. I figured they would either not find the problem, or they would. Until I get the car back, I'm not going to assume it's been fixed.

Studying the wiring diagrams, I've noticed that each coil gets two wires. One of those wires goes directly back to the ECU, without any splices along the way. I can replace that wire. I would have to figure out what kind of pins to buy to renew that entire wire, end to end. You have provided me with the part number for the replacement 2 pin connector to attach to the coils, I would need to know what pin/receiver to buy for the end that connects to the ECU.

The other wire is not as easy. The other wire all go back to some splice point, where it is spliced together again later down the line. I suspect that will be a much tougher wire to replace, end to end.