Fixed Idle problem on '85 5000S. Is it safe?

Reply Subscribe

Thread Tools

Search this Thread

Mar 15, 2000 | 09:46 AM

GEISTFREUND

Thread Starter

New Member

Joined: Mar 2000

Posts: 43

Likes: 0

Fixed Idle problem on '85 5000S. Is it safe?

I have been fighting an idle oscillation problem for several months. While messing with the problem again today I noticed that running the engine with the upper/lower idle microswitch connector removed seems to solve the problem. Is this condition safe. What do these two switches really do? (other than create headaches). The only noticable difference so far is a little less "pep" on fast starts, and a lttle slower idle recovery time.

Any comments????

Mar 15, 2000 | 10:32 AM

QCRAZY

AudiWorld Super User

Joined: Mar 2000

Posts: 9,281

Likes: 1

Re: Fixed Idle problem on '85 5000S. Is it safe?

I guessing here but I have seen similar switches on early 928's.

They had two as well, one was for cold starts the other was the load sensor. Sounds like you pulled the load sensor!!

Again, I'm just using an educated guess!!
What's everybody else think?
--
Andrew
95 90Q
91 90

Mar 15, 2000 | 10:46 AM

DaveN

Junior Member

Joined: Mar 2000

Posts: 675

Likes: 0

Are you talking about the throttle position switches?

Mar 15, 2000 | 11:17 AM

GEISTFREUND

Thread Starter

New Member

Joined: Mar 2000

Posts: 43

Likes: 0

Re: Are you talking about the throttle position switches?

That would be them. Two microswitches mounted on the throttle body casting. Haynes manual is very unclear about these two switches and thier function. The car runs much better now, I'm just wondering if other problems can occur because of running without them. (ie; fuel system over-pressurization, running too rich, etc.)

Mar 15, 2000 | 12:03 PM

Todd W

Junior Member

Joined: Mar 2000

Posts: 1,800

Likes: 0

Idle and full throttle switches, and what they do.

The idle one is what stopped your oscillation. The idle oscillation is most likely a vacuum leak. Disconnecting the idle switch is a temporary solution, but not recommended long term. It will mostly affect your fuel mileage if your oxygen sensor is in good shape.

Disconnecting the full throttle switch is a bad idea if you drive the car hard. You will be at the wrong fuel mixture at full throttle (actually anything over 3/4 throttle). This could lead to problems. Or you could just drive the car gently.

Get your vacuum leak solved, and then plug the connector back in.

Todd W

Mar 15, 2000 | 01:21 PM

DaveN

Junior Member

Joined: Mar 2000

Posts: 675

Likes: 0

I think the idle one turns on the idle stabilizer system...

like we haven't seen this one before. I had this same problem (several times in the 7 years I had the car), and it always turned out to be a dirty ISV. You need to be sure to set the switch up right also. If you adjust the switch with the car off you can hear the click as the idle switch closes, at that point you tighten the screws that hold the switch down. If you don't set it right you will either not use the idle system because the switch doesn't close on the throttle stop, or if too tight you will be using the switch as the throttle stop, and it doesn't last long this way. I have also had surging problems at full throttle when the other switch got dirty. This assembly is pretty easy to take apart (two small screwdrivers to unsnap the cover, there is one microswitch, and one open switch, the open one is the full throttle).

Mar 15, 2000 | 05:41 PM

GEISTFREUND

Thread Starter

New Member

Joined: Mar 2000

Posts: 43

Likes: 0

Re: Idle and full throttle switches, and what they do.

Thanks Todd, Dave, Fast.
I have re-connected the full throttle switch, disconnected the ISV, and everything is fine.(Thanks Todd). In effect I guess I'm using only part of the stabilization system. (cold start, warm-up, and compensation). I have tried to find the vaccumm leak without luck. It may be buried behind a panel somewhere. I think I will just leave it disconnected for now. (have the P/S pump to worry about first).

Maybe it should be called the
"Idle De-Stabilization System"

Later, John