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OK, the plan was to do a (very) poor man's smoke test with a cigar and maybe a glass of bourbon to complete the ridiculous picture, but I couldn't get the big hose off the brake booster without pulling out that white check valve. Not sure if that would be an Extremely Bad Thing or not, I left it alone and decided a preliminary vacuum leak test would be to see idle vacuum while running. Pulling the little hose that tees off the brake booster line off of the check valve and hooking up the gauge, I get 21 in-Hg. It's at sea level, but still...that seems awfully good...would a leak causing a high idle still allow it to be that high? Then for grins I decided to check it at the vacuum input to the EZF, and I get...0. Nada. (No, I'm not reading the vacuum from the EZF connector, but from the line going to it). That can't be right, can it?! Someone had a thread where they teed off this line to attach a permanent gauge, so something is definitely wrong here. I don't know that it would cause any of my symptoms however....thoughts?
...and serious contender for Dumb Question Of The Week: Where is this damn idle adjustment screw on the S3? I can't find a clear pic in the manual and looking in past the runners, from the front of the car, I see a screw and a red cap or something, to the right of the screw...but that screw looks like a mounting screw to me. Is it under that red cap? Is it the screw next to it? Something else?
Hey buddy, I just got caught up on your thread.
So 21 is good for vacc reading at idle. Thats where mine sits, and I confirmed no vacc leak on mine via smoke machine. So I don't think you need to put yourself through that just yet.
In regards to vacc line to EZF, I was that guy with the permanent gauge...
I would look at the seven way splitter, if your lines are stock configuration it should run from that thru firewall to your computer. You may have knocked it off rooting around with the ISV.
In regards to idle control, jump the diagnostic port, then look for the idle adjustment screw on the front if the throttle body.
Good stuff, the S4 boys are jelly because they can't do it like us....
take a vacuum reading from the front damper .
NOTE the port at the booster will always be hi as its sourced through the venturi port.
The idle adjustment screw is a 7MM brass headed screw,
its next to the red cap that is a vacuum plug
Hi Jeff
Currently have my throttle body out so took a shot of the 7mm screw which is to the left of the 2 vacuum plugs (plugged off air pump) plus the rubber mounting for the ISV clamp which fixes back to the throttle body mounting bolt. Sorry for the poor quality the light not too good.
7mm Screw for idle adjustment at rhe front of the throttle body
If I pull out that (venturi port? The white thing that the main vacuum line plugs into on the front of the brake booster) is that a problem? I don't think I can get the line off without doing so, and that seems to be the one to use if I do need a smoke test...
Operation of the ISV commences only when the idle switch on the throttle is true. Lots of idle problems are rooted in that switch and its wiring. The "idle screw" is adjusted to just keep the throttle plate from getting wedged/jammed in the throttle housing at full-closed position. On other cars I like to start off with a feeler gauge for that. If you decide to adjust it blind from the outside, use care that it doesn't end up too far closed.
Testing the throttle switch is best done with a DMM at the brain connector, with the connector pulled from the brain, battery disconnected. I don't have your wiring diagrams handy to give you exact pins to test. Verify that you have good continuity through the switch with the throttle at idle position, and that the switch opens as soon as the throttle is no longer closed. The switches get fouled with oil, and also tend to corrode a while after you wash the engine. You can start with the listen-for-clicking test as you manipulate the throttle under the hood, but you really need to prove the function with a meter.
I've done the "listen-for-click" test, and all was good, but it would definitely make sense to test it electrically. I will add that to the list of tests to perform, thanks!
I had time to do one thing today, and that was measure the vacuum at the line that connects to the front fuel damper. And that result was...0 in-Hg! 0! While at the brake booster it was 21. I'm off to look at routing diagrams to see what leads where, but that's two vacuum lines pulling no vacuum....I'm betting some type of junction has come loose (maybe that 7-way splitter or whatever it is) but I will chase it down. I really wish I had done this test before I started monkeying around with the ISV...it would be interesting to know for sure if this was something I just did vs part of my original high idle problem....but I guess that ship has sailed...
Update: Limited time again, but I pulled the air box and the MAF and looked around. Sure enough, found one vacuum line that was pulled out of the splitter. Put it back in, started it up, I now get 9 in-Hg at the front damper, and still 0 at the EZF. So, still a leak, but less of one I guess. Since the line at the EZF is still showing 0 in-Hg, I think that's my next known problem to chase down.
Went for a quick drive, POSSIBLY the dropping RPMs/potential stalling thing got marginally better, the high idle did not. It's high just sitting in my driveway (~1100 rpm) but when I drive it around, the idle is more like 1500 or more. Not sure if that's due to warming up or what.
My method here is to chase confirmed problems as I find them, which is why the EZF line is next up. Once I'm through that, if vacuum is still bad, time for that smoke test, if it's good (and everything is not running perfectly) then probably next up is the electrical testing of the idle switch.
OK, well this is a bit of a head-scratcher for me. I may simply not understand how some of this is supposed to be connected. The vacuum diagram ('86.5) I have shows lines coming out of the 7-way connector going to a port behind the throttle body (vacuum source, presumably), the two fuel dampers and fuel pressure regulator, the "AC kickdown," the EZF and (for me) a blocked-off port that would be for the auto transmission, if I had one of those. Well, my 7-way connector seems to have six ports, including one blocked one, and nothing leads from it to the firewall. I DO see the line coming from the firewall, but it connects to my EGR valve (?) or is that some sort of air valve, since it is in the hose that attaches to the underside of the airbox (I think from the air pump, which I no longer have). And I have an additional valve-like thing, over by the PS side of the engine bay, which is connected to my "AC kickdown" but which has an open port on the bottom.
This doesn't match the diagrams I have found. How is my EZF supposed to read vacuum if it's attached to a valve between the air pump and the air box? (I may be wrong, as the diagram mentions an EGR valve, so maybe that's not coming from the air pump after all, but...)
Yeah, so as is painfully obvious, I'm confused by what I'm looking at.
When you say 6 ports, does that include the vacuum source to the manifold? That should be the 7th way.
Which diagram are you looking at? The one from the MY85 Service Info guide shows the splitter providing vacuum to the A/T, EZF, fuel vapor recovery control, and all the fuel dampers and regulator. There's another line from the throttle body to the thermo switch, which goes to a different fuel vapor vacuum control. All direct connections to their targets, except for the line through the thermoswitch.
That is what the diagrams I have say should be there, but my splitter doesn't seem to have anything going to the EZF directly. I suspect something has been misrouted, or perhaps my car is a bit of a Franken-beast, with some of it containing earlier parts? Hard to say at this point.
My diagram does show an EGR and AC Kickdown but I read someplace else that those were not in use in the later years, and they do seem to have hoses going to the vicinity of that charcoal canister in the wheel well...I'll bet that's what those are, as you described.
05-29-2017, 02:59 PM
