Solid20vq

So I spent a good portion of the winter getting my beloved 1990 90 20v quattro in decent, reliable working condition, and thought (most) all was well. Now, after coming home from a summer job I have found that if the car is warmed up and the weather is warmer (80* plus) the car dies whenever I stop at a light or sign. I have found a vacuum hose that is disconnected and plugged with a golf tee, might this be the culprit? Any help would be greatly appreciated. Thanks in advance

yodasfro

I'd be looking at the crank sensors and or hall sender in the distributor.
Quick test on the crank sensors would be to poor cold water on them when the car is hot and won't start.

Lago Blue

That's where I'd start as it's as good a place to start as any. I did have a hot start issue that may have been similar to what Yoda describes above, but that had to do with re-starting <i>after</i> I had shut the engine off once warmed up, it still idled fine; and would not stall at a stop-sign etc.

You can read my experience w/ crank-sensors and my hot start fix here:

https://www.audiworld.com/forums/sho...ight=hot+start

...but I don't think that is your issue.

Summer is over and Audi school must resume, this is your next research assignment.

Air leaks are the bane of these engines as far as drive-ability and performance matters. As well as being a well-known cause of these kinds of issues, it is required house-keeping that you look at air leaking in as a possible cause as it is the cheap/simple place to start and may help prevent a great deal of unnecessary parts swapping that often otherwise occurs.

Engine idle-ability is contingent on careful metering of a very small amount of air. The key word is "metering" as the correct mixture control <i>cannot</i> be achieved unless all air being consumed by the engine, passes through and is measured by; the air meter. Any leak of air -into- the formal Intake or Vacuum Systems is especially unhelpful at idle speed, as any (un-metered air) leak then represents a much larger percentage of the total air-flow; compared to that with higher engine speeds.

The above is often why air leak issues are first noticeable at low engine speeds.

Since any leaks of air -into- the intake system (vacuum leaks included) cause the air-meter signal to be less useful, as it then tells the fuel system that less fuel is required, when more would actually be helpful; and may also cause the ECM to want to ignore the MAF and default to its maps which are biased towards too rich, finding and fixing air leaks is a necessary maintenance function we must not fail to do.

A secondary effect is that your Fuel Pressure Regulator requires the delivery of <i>full</i> engine vacuum at idle in order to back the fuel pressure off, down to the design number, but without that full vacuum it defaults towards full pressure. In addition, if the FPR cannot back the pressure off, it also cannot give it back during acceleration!

One might be tempted to think that the above two phenomena would tend to balance each other out, but what also happens is that your engine idle becomes unstable since the Idle Air Solenoid (or ISV, whose job it is to try and stabilize the idle at design speed by controlling air-flow), is being fed signals which cause it to reach the end of its working range; and it can no longer react in <i>both</i> directions (more air; or less air). When the ISV is not able to remain pretty much centered in its available travel, due to it having to remain off-set to compensate for air leaks, it can no longer react sufficiently to maintain engine idle; and a stall results.

This above situation sets up the conditions for the engine to stall precisely when you lift off the throttle when coming up to a stop sign for instance, rpm falls back to idle and the ISV -must- be able to react in both directions to achieve and maintain; idling.

Find the Vac System schematic sticker under the hood. Use that to find where that hose ought to go. All the components in the Vac System need to a.) function; and b.) not leak vacuum. The hoses large and small deteriorate with age. Remove them one at a time and inspect. Replace the crumbly/torn/cracked ones.

Go to 20v.org old style and see the idle troubleshooting stuff, ISV cleaning, crankcase vent update, etc.;

Learn to use the search function here to find archived conversations which may cover your issue, for instance:

https://forums.audiworld.com/search....archid=5799119

Go through the above and find idle screw O-ring etc. Consider that the Vacuum System encompasses more than just those items high-lighted in the official diagrams; every component from the MAF hose clamp to the lower injector O-ring and intake-manifold to head interface gasket is suspect till proven otherwise.

Get a simple Mity-Vac and learn how to do leak-down tests on sections of the vacuum System.

It may be that you simply have a dirty ISV that requires your attention, but if the engine bay hasn't been serviced in a while, there may be other issues.

Try to get The Bentley manual for your car, it's full of good stuff and the the diagram shown (Thanks Yoda!).

Hth,
Lago

Solid20vq

Wow, I never would have imagined such detailed and comprehensive responses to this problem, and I greatly appreciate it! Unfortunately, I am out of town and will have to wait at least a week until I can tear into her, but thanks to you guys, I have a solid idea of how to begin resolving this problem.
Thank you Lago and Yoda for your helpful responses, and as soon as I get back to my beleaguered quattro I will keep everyone posted as to my findings.
Thanks again!

Solid20vq

So it's been a long time coming, but here is my progress on this issue:

• Replaced breather hose w/ 034 silicone
• Traced vacuum circuit using the pages from lago:

Unfortunately there isn't a proper diagram for the early '90 7A; those from previous post are for the late '90 7A. I spent the better part of the day poking around, trying to find the home for the hose which had been plugged with a golf tee... I have found a few possibilities, which means there is another lonely vacuum hose somewhere without a home.

This is the hose I found plugged with a golf tee. (back of the intake and throttle body)

Today I also found the yellow hose disconnected; it runs to the fuel pressure regulator.

Now, the first possibility I found for the outcast hose is this elbow connector, which is high on the passenger side firewall. It connects to a clear plastic hose which runs into the passenger-side body, maybe to the diff lock?.


Upon further inspection I found a few more vacuum hoses which are disconnected; in the wiring running along the firewall are two white hoses.
I'm pretty sure the one pulled towards the camera connects to the pump in the top right of the picture (cruise control?).

White vacuum hose #2 comes out of the firewall on the driver side, along with a few wires.

It comes to an unsightly end, just barely visible beneath the battery.


Without the proper vacuum circuit diagram, I can only speculate as to where these three hoses belong. I wonder if there was another junction in the rubber hose near the back of the intake, to which White Hose #2 connects? I also have no idea where #2 goes.

In the meantime I am going to check the ECU ground, and I hear an improper connection in the back of the instrument cluster will cause stalling once the clutch is engaged. This is exactly what is happening to my car.

I've already replaced the crankshaft pos sensor, checked the hall sensor in the distributor, it looks okay.

If anybody could offer some insight it would be appreciated, thanks

IdahoDoug

I will take a look tomorrow (sunday) to see where the hose you found a T in goes to. Looks like yours has the same setup as mine. I'll also see what I can find on the other two hoses you mention. On the one with your yellow pencil pointing to it - was the golf T in the OTHER end? I'm going to post another thread in a minute asking a question you might know regarding the new silicone breather hose you recently replaced. If you can help, I'd appreciate it.

DougM

yodasfro

The connector on the firewall is for the battery vent.
I do have the early vacuum diagram I'll work on getting that scanned for you.
You should have a vac. diagram sticker on the underside of your hood too?
The hose that was plugged with a golf tee goes to the diff lock which is one of the plastic lines coming out of the firewall and should be pink. The other plastic line may go to the black/yellow checkvalve but I'd have to check my car to be sure.

IdahoDoug

Yep, Yoda's correct the line pointed to with your pencil goes to the pink difflock plastic tube coming through the firewall to the left of the battery. I'm going out again in bare feet to see where that white plastic tube you have "pulled toward the camera" goes to. Hang on.

Doug

IdahoDoug

And again, Yoda is correct. That white plastic line pulled toward the camera goes to a fitting on the bottom of that yellow/black bodied check valve you can see in the same photo (the plastic line literally crosses over it in the photo). On my vehicle that white line is black, FYI, and attaches with a couple inches of black fabric covered vacuum hose.

My feet are freezing! Heh..

DougM

Solid20vq

Thanks for the heads up;

Yes, the other end of this hose (pointed at w/ pencil) was plugged with the tee.

Now, the yellow/black check valve by the fuel lines is already hooked up to the small black vacuum line, so the white line must go somewhere else. I'm going to hook it to the cruise control pump as I run a few errands this morning, see if there's any improvement.


So then is the nipple above and to the left of the battery just to vent hydrogen? Or is that the Diff lock?

I'll also try to find the diagram, let you guys know what I find