Low vacuum


New Member
Hello, I just installed a mechanical boost gauge and its reading 15 inHG at idle and about 20inHG during deceleration. That seems a little low to me. The car starts and runs good, doesn't smoke. My question is can a bad IACV valve cause low vacuum? Because mine doesn't seem to be working; on cold starts the car doesn't idle high, it just idles at 1200 rpm and then settles to 1000 rpm when warm. Isn't it suppose to idle at least 1500 rpm when cold? Also I have the idle adjust screwed all the way in to get to 1000 rpm so that doesn't seem right.

Fast Guy

Staff member
I'm not sure on the vacuum reading. It's a bit better than mine, your compression is OK and your idle speeds are OK.