The post alluding to vapor lock is probably correct. The CIS system is
very sensitive to having sufficient residual pressure in the system
when the vehicle is hot. Often the cuprit is the check valve at the
fuel pump. If the smallest speck of rust gets caught in the check
valve it will not close, and the fuel will return to the tank, ergo a
loss of pressure. Often this can be heard, when the engine is turned
off, it sounds like a series of pings coming from the area of the gas
tank outet. It sometimes is immediate and other times very slow
depending on the size of the speck of rust or debris.
One can check this by loosening one of the bolts that seure the
banjo fittings to the fuel filter --- if the check valve is faulty,
there will not be a sudden release of pressure. if the check valve is
ok you will get a spray of gas. One should be careful in doing this as
one can get a facefull of pressurised gas if the check valve is ok.
On my 81,82, and 83 rabbits there is a hot start pulse relay that
is not integrated into the fuse panel --- it is in its own separate
holder, usually affixed to the fuse box by tape or a tie fastener -- i
have also seen them merely stuffed behind the box or dangling loose.
Since i do not have a 84, i'm not sure where its located, but when
functioning property, it causes fuel to be injected on an intermittant
basis in very short squirts during the initial cranking. Its called a
hot start pulse relay and Bentley shows its location on page 49 of
section 4, above the fuse box and say it is identified by its three
terminals and part no 813 906 064. Every post 1980 rabbit has the
relay.