81 911SC Constant high idle

lucasdw63 · 03-18-2008, 01:01 PM

Hoping someone can help me identify an idling problem I have with my 81' 911 SC. I recently replaced my alternator because my old one had a fried regulator. After I installed the rebuilt alternator and went for a start, the car fired right up. Unfortunately, my engine RPMs start and remain around 2500 with no change even as the engine warms up. I have about 85k miles on her and she is in otherwise perfection shape!

Any insight wold be appreciated!

austria3 · austria3's Garage

Could be a fault connection between the temperature sender and the WUR. Check the Bentley handbook for instructions. Or to start with check the 12 (or 14 can’t remember) pin connector on the left side of the engine compartment right in front of the fuse box

lucasdw63 · 03-18-2008, 02:20 PM

Stefan,

Thanks. I pulled the pin connector off and everything seemed OK. I reconnected it and restarted with no change.

Dan

Dennis Kalma · Dennis Kalma's Garage

Quote:

Originally Posted by lucasdw63

Stefan,

Thanks. I pulled the pin connector off and everything seemed OK. I reconnected it and restarted with no change.

Dan

A few possibilities, one is the WUR as described, you want to check the relay to see if it is buggered, I had the same high idle problem last summer, changed out all sorts of components (AAV and AAR) as well as the WUR and finally tried the relay. Problem went away. Just get another one and put it in place and see what happens.

If that fails, then there is the AAR (odd sort of part on the RHS of the engine, big pipes of about 1 cm ID going to it, between #3 and # 4 cylinder, right down by the head). It has a thermostatic element that leaks air when the engine is cold and it can stick open. Easy test is to just disconnect it and plug both openings (engine warm) and see if the idle settles down. If so, then it is bad and needs to be replaced.

Dennis

diy83sc · 03-18-2008, 06:30 PM

Sometimes the sliding window in the AAR gets stuck but should free when the engine is hot. Assuming your problem is not electrical, you can try tapping it free with a small block of wood.

Jim Williams · 03-19-2008, 11:54 AM

This could be an air leak around the throttle plate. Try blocking off the AAR,AAV and Decel valve. You can block off all three at the same time by removing the hose connection at the back of the air boot (which connects the air flow sensor and the throttle body), and plugging both the hole in the boot and the end of the hose you removed. This is the hose on the right front of the boot. If your idle drops back to normal, then a fault in one of the three, or a loose hose connection will be indicated.

It will take a little maneuvering to do this, as there is not much working room there...

Howard M · 03-19-2008, 03:39 PM

Don't rule out sticking advance weights, either. When was wthe last time they were cleaned and lubed?

Howard

rallyracer · 03-19-2008, 06:01 PM

Don't forget the super simple. Check the cruise control cable, if you have one. I've had mine get stuck a couple times after working in the engine bay. It's always a surprise, when you start it up!

lucasdw63 · 06:20 AM

All, thanks for the insight. I tried your recomendations to no avail. I was wondering if it is possible to have a leak around my pop off valve that would cause the high idle?

lucasdw63 · 03-23-2008, 06:21 AM

Quote:

Originally Posted by lucasdw63

All, thanks for the insight. I tried your recomendations to no avail. I was wondering if it is possible to have a leak around my pop off valve that would cause the high idle?

VaSteve · 03-23-2008, 06:49 AM

Check to make sure your new alternator is actually working properly. I had the same issue. I replaced a dead battery and didn't know the alternator had died as well. Once I changed that also, it worked fine. If all worked before, look at only what you changed in the situation.

Jim Williams · 03-23-2008, 08:56 AM

It is not likely that a pop-off valve leak would cause your high idle problem. A vacuum leak into the intake manifold is an "unmetered air" leak, that is a leak after the air flow sensor. This is outside air that has not passed through the air flow sensor. A leak of this sort leans out the mixture, whereas a leak through the AAR or AAV does not affect the mixture, as this is air that has already passed though the air flow sensor. Try lifting the pop-off at high idle, you should meet with significant resistance. If it is easy to lift, you have located a problem. Your engine should die right away.

Alternately, you can try some firm pressure on the top of the pop-off valve. Should have no effect on the idle speed.

lucasdw63 · 03-23-2008, 03:14 PM

Quote:

Originally Posted by VaSteve

Check to make sure your new alternator is actually working properly. I had the same issue. I replaced a dead battery and didn't know the alternator had died as well. Once I changed that also, it worked fine. If all worked before, look at only what you changed in the situation.

How would I go about doing that? Would an improperly functioning alternator affect the idle speed?

lucasdw63 · 03-23-2008, 03:15 PM

Quote:

Originally Posted by Jim Williams

It is not likely that a pop-off valve leak would cause your high idle problem. A vacuum leak into the intake manifold is an "unmetered air" leak, that is a leak after the air flow sensor. This is outside air that has not passed through the air flow sensor. A leak of this sort leans out the mixture, whereas a leak through the AAR or AAV does not affect the mixture, as this is air that has already passed though the air flow sensor. Try lifting the pop-off at high idle, you should meet with significant resistance. If it is easy to lift, you have located a problem. Your engine should die right away.

Alternately, you can try some firm pressure on the top of the pop-off valve. Should have no effect on the idle speed.

I wil try that and see what happens.

VaSteve · 03-23-2008, 03:38 PM

Quote:

Originally Posted by lucasdw63

How would I go about doing that? Would an improperly functioning alternator affect the idle speed?

Get a multi-tester and tell us the voltage across the battery terminals with the engine running.

We guessed that my failure to run properly was because the WUR didn't get enough voltage to properly warm up and thus the high idle trying to warm up the engine.

Paulporsche · 03-24-2008, 04:29 AM

Try disconnecting your O2 sensor and see what happens.

Also, did you say you disconnected and plugged your decel valve?

lucasdw63 · 03-25-2008, 04:43 PM

Not sure if this is related to my high idle issue, but I noticed my fuel guage only goes up to the 3/4 level despite just filling the tank; the oil Temp level never never increases; and the oil level never rises either. They all engage once the ignition is engaged, however it seems the idle remains at 2200-2500 RPM. One other thing I tried was to screw the idle adjustment all the way in to see what happened- nothing!

Appreciate all the help, I am determined to figure this out without taking it to the mechanic!

Jim Williams · 03-25-2008, 06:50 PM

Quote:

Originally Posted by lucasdw63

Not sure if this is related to my high idle issue, but I noticed my fuel guage only goes up to the 3/4 level despite just filling the tank; the oil Temp level never never increases; and the oil level never rises either. They all engage once the ignition is engaged, however it seems the idle remains at 2200-2500 RPM. One other thing I tried was to screw the idle adjustment all the way in to see what happened- nothing!

Appreciate all the help, I am determined to figure this out without taking it to the mechanic!

The air getting into the engine through the intake manifold has to come from somewhere. Metered air can get there several ways. 1) through the throttle at the throttle plate, 2) through the idle bypass passage (idle screw), 3) through the pipe at the Cold start valve. The pipe at the CSV valve connection to the intake manifold is fed by a) the Deceleration Valve, b) the Aux Air Valve, and c) the Aux Air Regulator. If you checked these last three (a,b, and c) per my earlier suggestion, that doesn't leave much. Have you actually checked the throttle plate to see if is being held open a slight amount by something?

BLEW911 · 03-26-2008, 05:19 AM

For what it's worth...my mechanic, Jason Duarte, solved a pesky high idle problem (sometimes as high as 2000 rpms) by replacing the distributor.It seems the advance was sticking.

Don

VaSteve · 03-26-2008, 02:46 PM

Quote:

Originally Posted by lucasdw63

Not sure if this is related to my high idle issue, but I noticed my fuel guage only goes up to the 3/4 level despite just filling the tank; the oil Temp level never never increases; and the oil level never rises either. They all engage once the ignition is engaged, however it seems the idle remains at 2200-2500 RPM. One other thing I tried was to screw the idle adjustment all the way in to see what happened- nothing!

Appreciate all the help, I am determined to figure this out without taking it to the mechanic!

Did you check the voltage?