Adam, I'm not sure we're on the same page here about vacuum leaks. Yes, there's vacuum that's used to assist the brakes (assuming that the 90 had the old/new vac. assist brake system), adjust the climate control, etc. That vacuum may be generated by an electric pump (like the power lock system) or a cam driven pump (like on the old 4k's) or syphoned off the engine intake using a check valve. When the (non-turbo) engine is running, the engine produces a vacuum - that is why air flows into it. There's a measuring device (in my 5k's, it's the CIS airflow meter) that figures out how much fuel to put in based on the amount of air flowing in. Between the meter and the engine, there's a vacuum. If there are any leaks in the plumbing between meter and engine, then unmeasured air will enter the engine and the mixture will get screwed up. From what I understand, the Smoke Test pressurizes the intake and leaks will let the smoke out. Most leaks will be found with this test, although I've heard that some leaks let air in, but tend to seal under pressure. The Bentley test is a good indicator of leaks in vacuum lines - which may be connected to things like emission controls, timing advance, etc. in which case the test is good. A Mity Vac is good for these tests, too, and gives you a gauge to read the leakdown. The test will not uncover leaks in any of the intake hoses, though. The propane gas test will suck in propane into the system, causing an increase in rpms - when the engine is at operating temperature and idle is stable, you'll have a fairly high intake vacuum to test with. Obviously, this is not a test to be done in a closed space....but you wouldn't be idling a car in there anyway, right? Cheers! Steve Sears
1987 Audi 5kTQ 1980 Audi 5k 1962 and '64 Auto Union DKW Junior deLuxes (SPAM Blocker NOTE: Remove SHOES to reply)"Adam" wrote in message news: snipped-for-privacy@4ax.com...