What can cause a rough idle inside the engine? Checked everything else.

[looks450]

2003 vy crewman, 180k dual fuel.

I have rough idle and here is what I have done to try and fix it.
New plugs and leads
Throttle body clean
Checked all vacuum hoses, and replaced the brake booster hose
Cleaned AFM, tps and that other thing on the side of the trotted body.
Reset ECU
Tested and checked coils

When I run it with one plug disconnected, it doesn't get any worse, no matter what cylinder is dead.

It doesn't seem down on power under load, but it's not really a performance vehicle.

Any ideas on what to have a crack at next or something that I have missed would be great.

I am just wondering what else it could be...

Thanks,

Looks

 

[VR38]

Compression test and vacuum test...

Worn valve springs, burnt, bent worn valve's and seats, worn cam, worn lifters, (most of this will show on a vacuum gauge if you know how to use one( will cause idle and performance problems.
So will damaged/broken rings.

Are you 100% sure you have a big fat blue spark when tested in open air thru a spark tester?

 

[looks450]

I didn't test spark, I just replaced the leads and plugs. I checked the coil by taking off two leads and watching it arc out between posts.

Thanks

 

[VR38]

What colour was the spark?

 

[looks450]

It was yellow i think. I might get a spark tester to get a better look at it.