i think you need one
on the vectra for example the air con pipe seats above the manifold and warms up very quickly without the heatshield
look close to the manifold to see if any fuel lines or coolant hoses or sensor wires are near enough to melt or crack
on the redtop and 1.8 / 2.0 ecotecs they commonly suffered from cracked fuel hose as a result of sitting on the inlet manifold and eventually cracking and splitting