it tend to be a maximum of 14 in/hg.

i wouldnt care much, except i'm boosted and thinking that this could be causing boost problems.

my first question is, if i had a vacuum leak wouldnt my car idle bad? My car idles rock steady at 750 rpm when warm, so i'm thinking it can't be it.

The other thing ive heard is that maybe my valve lash is too tight? does this really make 5-7 in/hg difference? needless to say, i'm going to be re adjusting that soon.

also, are there any devices hooked up to the vacuum system that could cause this? (I dunno, evap canister, brake booster blah blah blah)

help me out!

 

What is your map voltage? It could just be a wacky boost gauge.

Other possibilities..

Slight vacuum leak
Cam Timing off

 

how would i go about checking map voltage?

 

Mine reads 12in/HG at idle... is that not normal??

 

i dont think it is.

 

bump, more help!

 

Yes - tight valve lash could cause lower idle vaccum readings. A vaccum leak will not cause lower readings - it causes a hunting idle. As mentioned also, cam timing can have an effect too. Clogged catalytic converter is another reason for low readings. Anytime the a/f charge can't get out of the engine, vaccum suffers. You could grab a pressure gauge and meausre exhaust back pressure - just take out the O2 sensor and note the pressure at idle and around 3k rpm - they should be about the same.

My stock 99 hatch pulls about 19-21" at idle.

 

heh, good thing i dont have a cat

thanks a lot chris, that was the answer i was looking for. I'm doing valve lash asap needless to say

I'm also gonna make sure my boost gauge is functioning correctly by checking map sensor output voltages.

 

oh chris another thing,

i'm turboed, obviously this is a restriction in the exhaust. However I still think the vacuum is low, even for an FI car.

 

also, wouldnt misadjusted valves to the point of low vacuum also cause a low compression test result? I wouldnt say thats really teh case... pretty normal compression. 160's all the way across.

 

bumpitty

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by s1ngle &raquo;</TD></TR><TR><TD CLASS="quote">also, wouldnt misadjusted valves to the point of low vacuum also cause a low compression test result? I wouldnt say thats really teh case... pretty normal compression. 160's all the way across.</TD></TR></TABLE>

Hmm, not necessarily. Compression tests don't involve combustion or exhaust effects like a running engine. Plus, you crank it several times, so the pressure does "build up" a little bit. 160 seems a bit low for me, all the healthy D16's I've done were at least 180.

Side note, my turbo D with the Greddy kit pulled 20-21" at idle.

 

That's wierd... could it be a problem with the throttle body?

Check your map and TPS sensors.

BTW, my turbo D sits at 22-24 In Hg at idle... but I think the boost gauge is off a bit.

What kind of gauge do you have? Autometers are notorious for being a little off...

 

my sits at about 21

 

i have an autometer, thanks for the responses guys, as soon as it warms up a bit i'm doing a valve adjustment.

question: whats the best way to go about testing those sensors? although i'm assuming my helms manual will say, i'll check that.