So fairly recently i replaced my sparkplugs (well 5 of them cus the supplier shorted me one i did not know about until i went to install) but i did not have new coil gaskets.

car was running just fine after this.

so i now got the ignition coil gaskets and the remaining spark plug (#1).
put the gaskets in and replaced spark plug #1.
When i did this i noticed some of the wiring to the coils had become brittle and some areas of wire were exposed so i insulated those for now with elec tape.

when driving yesterday i noticed some intermittent fluctuations in my revs, 750 down to 500,
at one point under quick braking it dropped under 500 and then stalled out.
as the car warmed up it got a bit better.

when i got home i removed and reseated spark plug #1 and removed and reseated all the coil packs.

today when driving i still had the same issue.

now is it more likely that i got a bad spark plug or that i need new coils? Or my wiring needs replacing?
i will swap the spark plug back to the old one tonight and see if that fixes it.

 

What kind of spark plugs did you use? Did you gap them?

It does sound like a failing coil....I assume you found no oil in the plug wells.

 

i used the champion rc12yc plugs.
this issue only came up when replacing this last one.
i did not gap them as i don’t have anything to measure them. The other 5 have been replaced weeks ago and no issue. Possibly this last one is gapped incorrectly.
just recently redid my valve cover and gasket and there is no leaking at all from those.

i am unsure how old the coils are and i do know they certainly did not feel like they fit snug over the plug.
i am certainly leaning toward failing coil but at $65 each I don’t want to just buy them and replace them if not needed.
but feel i may have to

 

You can buy a 7th plug and swap it down the line until it goes away on a test drive

One may be cracked or bad manufacture and fails to produce combustion at the most crittical speed

 

if its the plug i assume its #1, the one i just changed as it was previously fine. With the 5 chamged previously.

good news is i know for now atleast my valve cover repair is working

 

You definitely do not want to buy a coil unless the spark plug ends up testing fine.

1. Swapping the old one back in is a good idea
2. A spark plug gapper is probably about $3.
3. A new spark plug should cost about $3 as well.

if none of that works, report back! Actually please let us know what happens either way

 

ok...
so...
it looks as though it is actually not a misfire.
looks as though the timing is just coincidental and that it is a vaccuum leak causing the revs at idle to fluctuate.

 

So we have a vacuum leak checklist ......

I am assuming you have a way to measure it but if not .....

See page 60 of the Jaguar 801s PDF

801S TITLE (jagrepair.com)

Do you have only one vapor canister on the left side just fwd of the rear wheel ?

Or 2 . one on each left and right side ?

That would make sure we are looking at the correct system , they mixed them up in production so there is no definite 1 or 2 reason like year or region

You will notice the cruise control is a separate isolated system from the rest of the vacuum lines

The idle air control valve can be fluxuating with the butterfly steady at the closed position

Removing the IAC valve can be X as he bolts can break off , loctited , 5.5 mm hex head bolts with very little clearance to get a thick socket on them

And if failing it is most likely after the IAC step motor has heated up and expanded and then by tapping on it while on a meter

The IAC does not have a follow-up position sensor to tell you it is stable with respect to the commanded position

So it can't be seen on a ELM - 327 device like a EGR error value , target 0

These are the 4 sockets on the ECU Black connector you can ckeck for loose sockets or corrosion


The step motor is wired like this , so you have X number of test lead combinations to look for a open ( bad )

 

Do not forget the intake manifold gasket. It wreaked havoc on my engine for quite a long time. Several shops apparently couldn’t find it, and I could not detect it blowing smoke into the lines….

I had an RPM blip that occurred every 32 seconds when at idle. When loaded up, with AC, headlights, etc, it would stall the engine out at times.