1990 300SE W126 vacuum system

[lepton]

LPG backfire on 1990 300SE W126 vacuum system

Hi all,
the car was running on LPG when it backfired and stalled while leaving a roundabout. The car will no longer start, though it does fire for a second or so. A search of previous threads suggests that a vacuum pipe has been blown off. Can anyone suggest which pipe and where it is located?

Thanks

Alan

 

[GEORGEROV]

Theres a vacuum pipe goes from the throttle body to the ignition control unit but wouldn't have thought this would prevent the engine from starting