Low vacuum idling, fine after driving.

[Whammydill]

I'm having an issue that cropped up yesterday with my idle. I was at a gas station and started my car back up. Idle is fine at 800-900rpm. Vacuum at 18 or so. I pull out of the station and drive it kind of hard the remaining mile to work. Decel vacuum was normal. All was as it usually is until I get to the parking spot. Idleing my car before I turn it off, it sounded really rough, and my vacuum is steady (very slight flutter) at around 10.5 mm/hg. I didn't have time to deal with it so I went in to work.

I start it up after work and it still idles at 10.5 and is rough, maybe even missing though I'm not totally sure what that sounds like. So I let the car warm up and drive it home. Driving, the car is fine. Shifts fine, pulls fine, like nothing happened. When I get home...my idle is back to 18mm/hg and smooth.

This morning I start my car and it is back to the 10mm/hg deal...

Now, I've read info on low idle vacuum from posts here and elsehwere and it said low steady vacuum at idle can mean valve timing? Do I just take off the timing belt cover and look? How would I know? What is the signifigance of the idle/vacuum being rough, then fine, then rough. Any recommendations? Boost leak test is in the plans as soon as a make/get another tester.

 

[agentorange313]

leak down test and compression test

Low vacuum is a sign of engine wear. It is one of the first signs of piston ring failure.

what rpm is your car reading at 10mm/hg?

 

[Whammydill]

800-900rpm @ ~10.5mm/hg.

 

[Whammydill]

Well, I went and got a compression test kit and some new spark plugs, and wouldn't it figure....rain. So it will have to wait. Meanwhile I have some more info that someone may be able to help figure this out with.

As I said, the car is idling low and rough when I start the car. After I drive the car for a while, it idles just fine and smooth. Today on a whim, I shut my car off after parking it and immediately restarted it and it's idling roughly and low again. That ring any bells?

I don't know if it is related but my waste-gate usually opens at about 10-11psi, but now it is boosting up to 13-14psi.

Also, I'm noticing the exhaust smell in the cab more. It smells a touch rich.

Hopefully I can post some compression numbers after this rain stops and I have the time. I will also try to post a video of whats going on. Thanks in advance tuners.

 

[96 420a-t]

W00t I'm the first. BLT!

 

[Whammydill]

I said it's in the plans.

 

[96 420a-t]

Sorry I must havemissed that. I think that you have a leak some where, but when it gets warm is swells or something to plug the leak.