I'm working on someones car. The car originally had a vacuum leak in the lower intake manifold to engine gasket. I replaced that and was very careful to put everything back together correctly (I've done this several times before). Everything runs great, bothe turbos operate correctly and it feels powerful. I've sprayed starter fluid all over the engine trying to find any leaks and it seems solid. Before the project, the car would pull about 16-17 in at idle. now it sits about 15 and sometimes will dip to 12. I did a compression test with a graphing compression tester before the work and all three faces of both rotors are well within spec. The car has approx 70k on it. The only mods are a downpipe and cat back. Does anyone have any ideas as to why the vacuum would be so low.

Thanks

Greg

 

is the rpm during idle at the same position as before?

 

every car (and every engine) ive had has had vacuum between 12-15in hg. I have noticed that most people who pull 20 in hg , idle at 1000. mine always idles at 750-850rpm

 

The idle is stock. About 750-850. It's the same as before. I'll check the manual for what it says about stock idle vacuum to make sure I'm not crazy. I'm pretty sure my rx-7 has about 17-18 at idle.

 

me too .

 

what kind of gauge are you using?? make sure it's accurate. my autometer cf ultralight reads 2-3 in/hg low and until i put a snap-on gauge on the motor, i thought something was wrong.

 

Mine use to idle at 750-850 and pull 12-15Hg... ever since I changed my plugs/wires I screwed something up with my intake though. Now the idle varies, with the cruise cable attached, it is guarenteed to be 1100-1200.. and I pull anywhere from 12-16Hg depending on the RPM it feels 'happy' at. Yesterday it was being bitchy and idling at 400-450rpm. I theorize my issue is in the 'warm-up plunger' as I had to replace that crappy TB coolant line and it may be pinched.

I think you're okay -- if it really worries you I'd pull the UIM off and re-seat everything. It may be the 'thermowax warm-up plunger' on the TB. On my car the above idle performance is completely uneffected so that may be something to look at as well given that lines odd placement.

I'm still learning a lot about the induction systems on our cars and the confusing issues simple things can cause. So take my words with a grain of salt.

~Kris

 

Well, my next approach will be to completely disconnect the guage (autometer, don't remember the series) and use a test guage. Thing is I have an autometer Ultralite on my car and it pulls approx 17 at idle. 15 isn't what bothers me, 12 does. I'm very sure it has no vacuum leaks. I've been doesing the intake with starter fluid with no reaction. This is how I detected the original leak and there was a noticable difference in how the engine ran when being sprayed. I hope I'm being paranoid. Thanks for the responses. Anyone else have any input on their normal readings? I'd be interested to see what the majority sees. I'm also having trouble finding a spec in the manual as far as what it should be pulling out of the factory.

Greg