Idle Problem

[KEYSTONE5]

I HAVE A 83 911 SC THAT WILL SURGE AT IDLE UNTILL THE MOTOR DIES. THE CAR WILL IDLE WHEN COLD BUT STARTS TO SURGE AS IT WARMS UP. THE CAR RUNS FINE BUT WILL CUT OFF WHEN I STOP. IT CRANKS RIGHT AWAY BUT WILL NOT IDLE . ANY IDEAS?...PLZ HELP

[Kemo]

oh man...there are a boat load of possibilities!

here is a rundown of the things that "could" be wrong.
1. Clogged Fuel Filter
2. Clogged Fuel Injectors
3. Warmup Regulator gone bad
4. Bad Fuel Pump
5. Gunky fuel distributor
6. Rust in the gas tank (prelude to #1 & #2)
7. Intake leaks
8. Bad Spark Plug Wires
9. Fouled Plugs

And im sure the list can go on and on...

I would suggest starting with the easiest things first, like New Plugs, Cap and Rotor. Then get a new Fuel filter and check your Fuel Injectors. You will also need some way of verifying fuel pressure, so you will need a fuel pressure tester. I hear they are cheap.

I think the best investment you can make right now is to get a book called "101 Projects for your Porsche 911". The author runs this board. I have one and I love it.

I think the reason nobody responded was because your proplem could be from so many different things. Get this book, run thru the basics and if you are still having problems, post again. At least you can rule out a few of the minor things. I have a 78 with an 82 engine and I went down the same road you are traveling.

Save yourself alot of money and time by getting the following:
1. Wayne's book "101 Projects"
2. Fuel pressure tester
3. Gunson CO gastester (optional but would be really cool to have)

Good luck and keep us posted.

[MotoSook]

Keystone, Welcome...

....perform a search using "AAV", "AAR" or "Decel Valve" search words.


A little more history on the problem and/or car would help.

[KEYSTONE5]

THAKS FOR THE REPLYS...CAR HAS 148,000 MILES. NO HISTORY ON CAR. MOTOR IS VERY STRONG FOR THE MILAGE SO I FEEL PRETTY SURE WORK WAS DONE. RECOMMENDED UPDATES WERE DONE IE . TENSIONERS ECT. ENGINE VERY CLEAN. MINOR TUNE UP DONE 7,000 MILES AGO. NEW OEM PLUG WIRES,DIST CAP, ROTOR. PLUGS . MIXTURE SETTINGS ECT. CAR PASSED EMMISIONS WITH COLORS. SURGING IDLE JUST STARTED 2 DAYS AGO AFTER A HEAVY RAIN. THE A/C SYSTEM HAS BEEN REMOVED COMPLETELY SO A GOOD AMONT OF WATER COULD HAVE FALLEN THRU THE DECK LID. COULD THIS CAUSE THIS TYPE OF PROBLEM? THE FUEL FILTER HAS 11/99 ETCHED IN IT SO THAT WILL BE REPLACED. WOULD A VACUM LEAK CAUSE THIS PROBLEM?

[targa80]

Keystone5:

WHY ARE YOU SHOUTING?

This can also be a problem with the mixture control. Once warm the idle can surge high and then drop low to the point of stalling. Warm the engine and disconnect the O2 sensor plug and see if idle settles out. If it does either your O2 sensor is bad or you need to readjust the fuel /air mixture.
Recently I posted info on the sequence of the cold start to warm engine theory.

Here is the theory of the Kjetronics with lambda operation from cold start to warm operation. It might help you in figuring out your problem.

The Lambda (O2) sensor requires high temperature to operate properly. With the O2 sensor connected and the engine is cold the Kjetronics with Lambda system operates in the open-loop mode. The lambda control unit does not have a valid signal from the O2 sensor at cold start To correct drivability problems at cold start a lambda thermoswitch is installed to give the lambda control unit an additional input and insure proper fuel metering during warm-up. When the engine is cold, the thermoswitch is closed. the lambda control unit sends a fixed, slightly-rich duty cycle signal of 60% to the lamba control valve (frequency valve). when the thermoswitch warms enough to open, the control unit sends a fixed middle signal, 50% duty cycle to the frequency valve. When the lamba (O2) sensor reaches operating temperature so its signals are valid, the control unit switches to closed-loop operation. In closed-loop oeration the duty cycle signals are constantly changing cycling back and forth from 45% and 55%. so the air-fuel ratio is maintained near stoichiometric; lambda=1.

So disconnecting the O2 sensor at a cold start would do nothing to effect the running of the engine. A bad thermoswitch would effect the running of a cold engine since it would not provide the necessary signal for the control unit to run at a 60% duty cycle. Instead the control unit would put out a 50% duty cycle.

When the engine is warm and the O2 sensor is disconnected (open-loop) the contol unit would put out a constant 50% duty cycle.

The thermoswitch is something you can check for proper operation with a meter.

[KEYSTONE5]

TARGA 80,THANKS FOR THE INFO......SHHHHHH..i will give it a shot and see what happens. i will post results....thanks again...keystone5

[targa80]

Now that is better, thanks for the quieter reply and good luck with the troubleshooting.

[KEYSTONE5]

I had the car checked and the warm up regulater was the culprit. The car was running rich. 30 min later and all is well....thanks again for all the info. Keystone5