Shuddering vibration on light throttle

[alanrlow]

I have a 1997 FZJ80 Series automatic LandCruiser with 300,000 kilometers on it. I have just had the valve shims done and the injectors cleaned, new plugs and air filter. I recently had the old vapor LPG system changed to a vapor sequentially injected LPG system. The performance difference is remarkable, as much if not more power than on petrol. Recently however it has developed a strange intermittent shuddering that can best be described as like driving on a corrugated dirt road, the steering wheel and dash shake quite violently. It only happens on a very light throttle. The moment I lift the foot or press a bit harder it stops. It happens at any speed from 60kph up to 100kph on either fuel so it's not fuel related. I have a vague recollection of reading something about a throttle position switch causing something like this but I can't find the thread. Anyone got any ideas what is causing this juddering?

Regards,
Alan.

[MWP]

Is it the engine shaking, or could it just be the steering?
Im wondering if its power steering pump related.

A shake like you described make its sound gearbox/driveline/steering related, not engine.

[alanrlow]

Is it the engine shaking, or could it just be the steering?
Im wondering if its power steering pump related.

A shake like you described make its sound gearbox/driveline/steering related, not engine.

I very much doubt it's engine related, it runs smooth as silk, but the shuddering can definitely be instigated and stopped by judicious throttle use. A very light throttle (just enough to maintain a speed) will often start it and lifting the foot 1/4 inch or pressing a 1/4 inch harder will stop it instantly. I'm leaning towards driveline. Thanks for your reply..

[oldcorollas]

look for play in any driveline joint to begin with.