Discovery TD5 engine starts shaking occasionally when started

Good afternoon

Recently my Discovery series 2 TD5 automatic from July 2000, started to develop a problem that our garage here in France (Tarn) has thus far not been able to diagnose. His diagnosing equipment, he tried three different ones, do not see all of the car's systems. When starting occasionally, i.e. not always, the engine starts to vibrate intensely and the gas pedal does not appear to respond when pressed. When it does not vibrate, the car responds normally to pressing the gas pedal and one can drive with it. Never had this problem before, and it started all of a sudden a few weeks after it had been sitting outside in winter under a cover. Would anybody have an idea what could be the matter and what part is worth trying to replace ? I have a short video of the engine doing the weird vibrating, is it a timing issue, fuel injection issue ? But landyzone does not allow me to upload it, probably size of file I imagine.

Many thanks as always for any suggestions.

Hi, that's not something to be diagnosed without watching live data while it happens or it can become very expensive to replace parts based on guesses .... though next time when it happens unplug the throttle pedal's connector and if it goes back to normal idle then replace it, i've never unplugged one with engine running so i dont know exactly if it will idle or stop completely, if it stops this test is irrelevant, also check the ECU red plug, if it's oil replace the injector loom... for any other issue a capable diagnostic tool is needed handled by somebody who knows Td5s... i doubt that a timing issue would be intermittent, ... can't help you more sorry