You’re right that under normal conditions fuel shouldn’t be traveling “upstream” into the intercooler plumbing, since injection is at the ports. The two ways I’ve seen fuel end up in the charge pipe near the throttle body are heavy flooding with repeated cranking where fuel wets the manifold and can get redistributed by reversion/pulses, and a fuel source that’s actually connected to a vacuum reference line.Tom wrote: the injectors fire straight above the head on the 944, after air has been pulled through the filter, turbo, intercooler and its pipes, and intake manifold -- the injectors sit at the very end of that path, so very unlikely that fuel flowed upstream against the flow of vacuum to pool in the intercooler pipes. A leaking fuel pressure regulator is common, however, and could spread fuel around the intake path. I would be inclined to quadruple check for signs of gas in any of the vacuum lines, including the one to the bypass valve.
On the 951, the most important “vacuum line fuel check” is still the FPR and the damper because if either diaphragm leaks, it can dump raw fuel straight into the manifold via the vacuum hose. If those are truly dry, I agree it’s worth expanding the check to any vacuum lines that see manifold vacuum and could potentially carry fuel if something is misrouted or compromised, including the bypass valve reference line and any tees/check valves in that area. I’d also sniff for fuel at those lines, not just look, because a small amount can be hard to see.
One more practical angle: if there was pooled fuel in the intake manifold from the earlier injector leak/flooding, it can sit and then get pulled into the engine on the next start attempt, making it smoke and stink even if the current mixture problem is actually a vacuum leak or idle control issue. Draining/cleaning the intercooler and pipes you had off is still worthwhile just to remove that variable.
If you want a quick sanity check, pull the bypass valve vacuum line and see if it smells like fuel, then recheck the FPR/damper lines immediately after a key-on prime and a short crank attempt. If fuel is showing up only after cranking, that’s a stronger clue something is actively leaking under pressure rather than just old residue.
