'99 Cavalier Z24, Manual. Ever since I got the vehicle, i've been trying to figure out what makes my car stall/idle rough intermittently, mostly when cold. I had it on a scanner today and i noticed something, what i think, is odd about the MAP sensor. It's reading 8.0in hg (Barometric pressure or vacuum?) at idle, and drops to about 5.0in hg when i blip the throttle. Is this a normal MAP sensor reading?

Thanks for any help.



99CavyZ ~ Black ~ 5-Speed
"If It Bleeds For A Week Straight, How Come It Doesn't Die!?"

the vacuum will drop when you open the throttle.



Gilles
2.3 Ho

I know...but should it only be reading 8 in hg at idle? also, when i cut the ign. off, it jumps to 28 in hg when the engine off, key on.



99CavyZ ~ Black ~ 5-Speed
"If It Bleeds For A Week Straight, How Come It Doesn't Die!?"

Key-off reading is right, it'll read 'normal' outside pressure. With the engine running, the pistons are creating a vacuum, giving you a reading of 8. Higher flow/less restrictive intakes read 9 or 10. Getting a 5 at blipping would indicate the engine is pulling in more air than is naturally available (vacuum) in the intake manifold. A 5 is probably too low, I only get a 5 or 4 when downshifting, and then it's only brief. My best guess is that there's constriction/blockage somewhere? What've you got for an air filter?

K&N Air filter, Cosmo Racing Intake (a cheap version of AEM)



99CavyZ ~ Black ~ 5-Speed
"If It Bleeds For A Week Straight, How Come It Doesn't Die!?"