Friends KF has a bad idle.
We changed leads, plugs, rocker cover and plug seals, cleaned the intake and the idle has become a lot better but it still is a bit jolty
Just wondering if anyone could know what this is?
Maybe a common issue or something?

Very common in the 3.5L.

Bad news is that there is no fix for the problem. What you have done is a good help though.

Best thing to do is to take it to a dealer and get them to raise the idle to about 1000rpm via their plug in computer and this will help get rid of the roughness when you are in gear at a set of lights. Just puts a bit of pressure on and helps get rid of the lumpyness.

People try and adjust the idle speed screw on the air intake but this is only good for a day or so because the car automattically lowers the idle itself so in the end, you have the idle screw fully out and the car has adjusted itself and you are back to square 1.

The only way around it is to program the idle via the hand held computer thingy Mitsub plug in to your car.

Sorry for the bad news mate. I have done absolutely everything and replaced absolutely everything with no real fix of the problem.

On the autos, a lot of people just live with
shifting the gear to neutral when car is idle. :(

Some say changing engines mounts help, but probably only
marginally.

Interesting
Though there definately must be a cause for this just no one has found it yet

When feeling the engine at idle it jolts as well so maybe it's an ignition problem? Or a missfire of some sort?
Maybe distributor?

Tried all of the above, including engine mounts with an upgraded mount that is ment to solve the problem.

Still rough idle. I have thrown so much money at this problem and still no fix.

I have just up'd the idle and all is fine. When it is in N it idles at 1000rpm and about 850 when in D and this has fixed the problem to an extent and no, it doesnt jolt when going into D from N. Cant even feel it.

yeah increasing idle rpm would be the simplest way that helps
as well as selecting N when stationary.

throwing time and money at it will just annoy the hell out of you.
i gave up after changing rubber engine mounts and 6 irridium sparks,
others have changed much more and still no change.

The plugs are platinum in it now
Leads, plugs, seals etc have made a massive improvement (probably less than half as rough now)

I realise it's probably a trial and error thing which in the end due to the cost involved is not worth it but like mentioned above I believe there is a solution to it.

It's also not my car and therefore not my decission of whether it will be left like that or not. We'll try raising idle but will take it to our mechanic which is awesome with cars and hopefully he'll know (as usual) exactly what the cause is

I'll keep you guys posted with results