hey guys, got an '84 XJ6. i got a little bit of a rough idle, and when i slow down, you can feel the trans bogging the engine down. so far all i've done is clean the inside of the dist cap (already arcing buildup only after a few hundred miles) fixed the bad vacume hoses, and checked the gap at the throttle plate. parts on order: new cap, new coil.
i pulled a couple of the plugs, they looked ok, so i dont think its a missfire. i guess really any of the plugs could be bad...
i've been doing alot of reading, and everyone says to start out at the throttle plate. i trimmed down a feeler gauge to a sliver, as to get a more accurate result using a flat gauge in a round hole. that ended up bumping the idle up to about 1250 RPM in park, and it drops down to about 900 in gear.
since the idle is so high, it makes a really good clunk going into gears, and the tach jumps way down, and its almost killing the engine. i've checked transmission fluid level, i think its good...
also when slowing down to a stop, the tach starts bouncing again, and before i did the throttle plate adjustment it would cause the engine to die.
just looking for some feedback on what to check next.
i have a manual on CD, but that makes it kinda hard to read, i'm more of a paper manual guy myself.
i'm willing to do what it takes, i consider myself mechanicaly inclined, just need a little guidance on this new and unfamiliar car.

 

Guys have been fighting "a little bit of a rough idle" on these cars for years. Usually it's a stack-up of issues, as described here:

tipofmonth7 - Rough Idle Remedies for 4.2L FI Engines

After the obvious and easiest things have been addressed I'd jump to having the injectors professinally cleaned. Personally I've found it to help the idle quality of all three Jags Ive owned

Jaguar Fuel Injector Service






Now that you've adjusted he throttle plate you need to adjust the idle speed dwon to a more normal range. I find 900rpm in "P" usualy works well on these cars

Idle Speed Adjustment




As you slow to a stop the transmission shifts down into 1st gear. With the idle so high you'll really feel the downshift and the tach will jump up a bit

Trans level is best checked after a 10-15 mile drive

There is athrottle vavlve cable ajustment for the transmission but I wouldn;t go there jst yet. Adjust the idle first.

Bear in the that the Borg Warner transmissions on these cars are a little bit clunky even under the best of conditions. It's not a bad trans but it' a very old design with roots going back to the early sixties



Get the idle speed lowered first and then report back

Cheers
DD

 

those are some handy straight forward tech articles. ill have to bump the idle back down and hopefully that will solve the clunking going into gear. i fear to really smooth things out its going to take going over everything.
is there any tech write ups to check timing? i assume its as simple as pointing the gun in the right area. vacume lines connected/disconnected?

 

Yup, that's about it.

Vac hose disconnected.

Cheers
DD

 

well I'll be....1984 XJ-6 are showing up like crazy in this forum. Where have they been all this time?

ok: there is a cure for rough idling that I learned from a Jag owner years ago:

SO WHAT IS IT? HURRY HURRY!

add a Ground Strap to the Oxygen Sensor. It cured my rough idling. I liked it so much I started making them for other owners. Here's pictures of the ones I can make. This mod works only for 1980 thru 1984 XJ-6 with 1-wire Oxygen Sensors, so if your car is 1985 thru 1987, you don't need this:

NOTE: I've had a O2 sensor ground strap in my 1984 XJ-6 since around 2000, it idles fine, it starts from the first crank. Curiously, 1985 and later XJ-6 O2 sensors came with a built-in Ground Wire from the factory. Go figure...

assuming everything else is good with your engine, (timing, ignition, etc.) then the Ground Strap will improve your idling stability. WHY? looks like the ground becomes poor as these cars age, so the O2 sensor does not communicate very well with the ECU. The ground strap "restores" the O2 sensor's communication with the ECU. Otherwise, I am not a rocket scientist, all I know is what adding the ground strap did for my car.