Just need some reassurance regarding the AOS on a C4...........

[Johnny-5]

In a previous thread somone mentioned something about my AOS so I did some research on it as well as talking to a few shops and would like to confirm a few things. I just went out to the car and started it up and Im not smelling or seeing any type of smoke coming from it. Ive also removed the oil filler cap pretty easy and noticed that there is some vacuum to it. Im being told this is normal. Car wasnt fully warmed up or anything so should the car be fully warmed up?

If the AOS is bad there would be smoke on startup and when removing the oil cap would be extremely hard or impossible to do depending on how bad it is? Also if the oil filler cap was removed it would drop idle or something die on you?

Can someone confirm this?

[JFP in PA]

The AOS (when new and correctly functioning) should show a vacuum of about 5 inches of water at the oil cap with the engine running (temp is pretty much irrelevant). When the AOS craps out, the vacuum level at the cap sky rockets to several times the correct level, making it nearly impossible to remove without a substantial degree of effort.

It is also not uncommon for the engine to stumble or have the idle speed change with the cap is removed (remember, you just vented an engine vacuum source).

Edited May 24, 2012 by JFP in PA

[boldstep]

My AOS catastrophically failed not too long ago so I can tell you my telltale symptoms that I ignored right before it failed. The idle was rough. That idle problem got progressively worse until sometime at a red light the engine would just die. There was also white smoke on most mornings after start up. RIght before it failed the check engine light came on. Then within 1 day, driving down the highway white smoke started pouring out of the exhaust. After the AOS replacement the idle is quite controlled and I hardly see any white smoke when I start her up.

[Johnny-5]

The AOS (when new and correctly functioning) should show a vacuum of about 5 inches of water at the oil cap with the engine running (temp is pretty much irrelevant). When the AOS craps out, the vacuum level at the cap sky rockets to several times the correct level, making it nearly impossible to remove without a substantial degree of effort.

It is also not uncommon for the engine to stumble or have the idle speed change with the cap is removed (remember, you just vented an engine vacuum source).

Thanks for the additional info. Ill probably get it checked sometime next week to make sure everything is up to par

My AOS catastrophically failed not too long ago so I can tell you my telltale symptoms that I ignored right before it failed. The idle was rough. That idle problem got progressively worse until sometime at a red light the engine would just die. There was also white smoke on most mornings after start up. RIght before it failed the check engine light came on. Then within 1 day, driving down the highway white smoke started pouring out of the exhaust. After the AOS replacement the idle is quite controlled and I hardly see any white smoke when I start her up.

Im not seeing any sort of smoke, rough idle or stalling so I think I should be ok for now at least!

[logray]

[Johnny-5]

http://www.renntech....-for-a-bad-aos/

You rock! Thanks for the link!