Does anyone know what is the correct intake manifold vacuum for an 81 308 GTSi? The idle on my car has always seemed rough so I checked the intake manifold vacuum on my 308 GTSi. It was holding steady at 20 at 1000 rpm. That seemed low to me so I disconnected all the vacuum hoses and it was still at 20. I know that would be low for a carb car, but I don't know what an FI car should read. I sprayed around and don't see any leaks, but I don't know if I really have a problem.
I should have been clearer in my original post. The vacuum is at 20 cm, which is about 8 inches. It sounds like this must be too low. Since the needle is steady I did not think it could be a valve problem, but could the cam timing be off and causing this? Thanks for your replies.
According to the Mondial 308 wsm, normal vacuum for an injected 308 at an idle of 1000 rpm is 260 mm Hg (10.23 inches of mercury, note the units). This is in stark contrast to what we muscle car guys are used to, a typical Detroit V8 has a vacuum of around 18 inches of mercury at idle. I too was taken aback when I put a vacuum gage on my 308 GTSi for the first time and saw that it only registered 10" Hg vacuum, I was relieved though when I consulted the Mondial 8 manual (page D5) and saw the spec. Yes, your vacuum reading of 8" Hg is a bit low and should be followed up by a compression test and leakdown test, if you really want to know what's going on inside the engine.
