Xj6 series 3 idle speed
 

1982 series 3
I was wondering what the idle speed should be at a red light in a perfect world with these cars. I seen on the hood it sais 700. When I come to a stop when the car is warmed up it fluctuates from 800 to 900 but never stalls. I'm guessing it fluctuates because the tanks need cleaning because I have drained them and checked inside with a light so I'm not too worried about that. Is this speed a little too high? Does something need adjusted?

Hi ahunt4,

When you did this, was the climate control turned on?

These cars where built pre idle compensation, meaning that there is no allowance for the a/c compressor as it kicks in or out.

As this operation drains 150 - 200 revs, the engine should idle a bit high, say 800 - 900 if the system is not on.

If the a/c system is on and running correctly and you are idling at 800 - 900 then, yes a little high but no biggie, mostly just heavier fuel use.

And these engines idle happier a little rich rather than a little lean.

As for 100 rpm range, don't expect an xk engine to hum at exactly the same revolutions at idle, they just don't.

Cheers,

Nigel

Don't worry, your idle speed is within an acceptable range. Of course if it gets too high, (like over 1000 revs) the car will creep more when off-throttle, and also you'll get a bigger 'clonk' putting it into Drive.

Hi ahunt4,

My 85 xj6 idles very happily at around 600 RPM with climate control on

Cheers,

Nigel

My Series 1 has AC and does the same thing, at least after a longish drive. I always wondered why but Nigel's explanation helps a lot. Thanks!

When I park the car, moving automatic gear just past reverse into park I also get a significant "clonk," as Fraser puts it. Is that also to be expected? Gears otherwise are smooth in operation and at start up.

Graham

Hi Series1fan,

Older technology like our Series III's means 'old school' happenings and getting to understand and appreciate them.

In this current world of seamless shifts and whisper quiet everything, it's nice to be reminded about how things were in the good old days.

Thant clonk. It's either as Fraser points to a slightly high idle or the diff just doing its' thing as it slows from a crawl to a stop.

All being well with correct oil level and working seals in the diff, as was mentioned many years ago, 'these aren't the droids you're looking for...'

Cheers,

Nigel

Thank you, Nigel! I had the diff rebuilt a year ago and I'm vigilant with fluids so I think I'll put it down to the somewhat agricultural feel of the BW12: though driving it's smooth.

It's a relief b/c I have other things to get sorted on the car and I'd like to see my to-do list shrink a bit.

Cheers,

Graham

Over the years I've come across a few Series IIIs that really complain if asked to idle at 600-700 rpm in "D".

It seems there is quite some car-to-car variance in amounts of a/c compressor drag and transmission drag. Add to that the (presumably) slightly leaner fuel mixture at idle on USA cars. Add the that the toll of age and mileage: perhaps injectors a bit dirty, for example.

You can beat your head against the wall trying to ferret out an obscure fault....or you can simply tweak the idle speed up a bit. We all make our choices :)


Cheers
DD

Hi Doug,

In Melbourne, Australia, in the day, it was common for the dealers to set the fuel mixture a little richer than the factory setting to help with a smoother idle.

In fact quite often, this was done pre delivery (before the car was sold for the first time) so that the customer would never complain about a funny idle.

In the 80's fuel was cheap and smog?, ...what smog!

Cheers,

Nigel