Carrera idle problems

[Mark 84 Carrera]

I'm having more trouble with my '84 Carrera. I hope someone can help!

1. Rough idle at fist startup after sitting a long while. It stutters, revs up to 1500, back down to 600 stuttering, several times before idling at 1000.

2. Hessitation on acceleration from rev.s below 3000. Actually, loss of power at low rev.s all the time.

3. When hot, from sitting in stop and go traffic, the idle begins to oscillate. It dips down to 800 then surges to 1200, over and over, constantly and quickly.

4. Last, a few days ago and about 30 minutes into a long trip, it lost all power below 3000 RPM and bucked severely. I had to keep the rev.s above 3k just to drive it. It idled as if it was just started, around 600 and very rough. The next day, it ran normal (see above for 'normal'.)

Bought the Bentley Manual. Checked the: head temp sensor, throttle position sensor and switch, air flow meter, idle setting. I also replaced: oil breather hose, crankcase breather hose, misc. vacuum hoses, air filter, fuel filter, plugs, O2 sensor and intake manifold gaskets. I cleaned the fuel injectors. I inspected all other hoses. I had a local Porsche repair shop adjust the valves (he found nothing else wrong.) I had the dealer check the fuel pressure and emissions after the bucking incident (he found nothing else wrong.) Anyone? What else is there? Why the oscillating idle when hot? What does temp. have to do with it? The head temp. sensor was within limits given by Bentley. HELP!

[Joeaksa]

Mark,

Can help you with one of them! On my 85 3.2 it did the same "hunting" at idle, sometimes all the time and sometimes it was fine. The tech were my car is worked on said that it was the "idle valve"...

He switched it out (its staring you in the face when you open the motor hood, 10 minutes to change) and immediately it settled down to a nice smooth idle. Best $130 I ever spent on a 911!

This is my idea on #3, although this valve may be the problem on #1 as well.

Joe

[GIBSON]

My '86 does the same thing when warm, fluctuating idle withing the same range as yours. This problem has been discussed in fairly recent threads. Someone mentioned replacing a hose from the rear of the throttle body to another location I can't remember. I have not had time to look at mine but that hose may be your problem. Hopefully that board member will reply.

Bruce Herrmann

[turn6]

Mark,
Does your car have the original cylinder head
temp sensor? The updated 2 wire replacement cured my car of similar symptoms.

MKoury

[Mark 84 Carrera]

I originally thought the temp. sensor was the problem, so I bought a new one ($80!) and went to install it. There was already a new-style sensor, 4-wire, looking shiny and new, so I bought the book to find out how to test it. It tested within the range and the ground circuit tested fine so I took the new part back to Porsche for a refund. I'll try to rig a remote test meter on the leads to monitor the value in the car.

I'll look in to the air bypass idle valve. It looks like a very simple part, though (it is never anything simple!)

[twin plugged targa]

Mark I HAVE been in your shoes beleive me!.
Took me 5 weeks a useless Porsche mechanic and $1,000 of his wasted time for the guys here to finally come up with the answer!.
You have not stated if you have inspected your distributor cap and rotor!.
Look at it immediatley!!!!.
Look at the condition of the carbon contact it should be at least 6mm/ 1/4" long and the cap in good condition.
If they are in poor shape replace both - they are only cheap!.
If they are damaged at all remove the distributor and check the end float of the drive unit!.
With the rotor pointing at the little notch in the dist. undo the only nut holding it in place and gently remove it(you may have to wiggle gently).
Tape the rotor in place so you dont lose where it should be.
If in doubt post a pic of the lower section of the distributor.
Once I had fixed this problem the engine still oscillated. I removed the O2 sensor and cleaned it with electrical cleaner and she ran fine!.
If you have done the DME harness test and the sensors are all sending good info then it may be your dme -but unlikely!.
I beleive your problem is something simple like mine was!.
Do not overlook anything, never rule out anything definatly esp. head temp sensor. Mine tested OK but I still chnaged it out! along with coil and dme relay.
Hope this helps.
Let us know any symptom result updates- do not send it to a garage unless you have a guy you would trust your girlfriend with, or very deep pockets!

[Jim T]

Have you checked to make sure the intake bolts are tight and the gaskets are good?

Common problem on the early Carreras.

[twin plugged targa]

Hey Mark,any update?

[adamnitti]

mark-

the idle valve is pretty expensive (+- $140), so you want to make sure it's the culprit before changing it out. your idle speed control valve should vibrate with the key on. the vibration should not be erratic, but steady. if you take it off, listen for the little piston in there to move if you shake the valve hard.

the bentley manual shows that the resistance between its outer terminals should be 40 ohms... between the center terminal and each outer terminal it should be 20 ohms.

hope this helps-

------------------
Adam Nitti
ajnitti@mindspring.com
www.adamnitti.com
'85 911 Carrera Coupe
PCA member, Peachstate region

[nhromyak]

Mark,

86Ragtop mentioned it already, but you should carry a spare DME RELAY anyway.

Have you replaced this?

This seems to be the cure for many intermittent problems.

Also, I have not heard of a 4-wire head-temp sensor. Are you SURE this was the head temp sensor? I suppose it was since you checked it at cold temperature readings.

GOOD LUCK!



------------------
Nick Hromyak
'85 Carrera 7 & 9 Fuchs
Havin' Fun in Sacramento

[Mark 84 Carrera]

Gentlemen,

Thanks tremendously for your suggestions. Today, the car ran warm and the idle began to oscillate as I mentioned earlier. I tried to unplug the O2 sensor while it was doing this, and as I was turning and tugging on it, the problem stopped and the car idled like it should. Hmm...maybe a clue, maybe not. I certainly can't work on it in this 100 degree heat. This weekend I'll do some more investigation.

BTW, the Temp Sensor is a TWO wire, not four. Ithas a nice clean, clear jacket over the two wires and the ground to the sensor checks out fine (which is the problem with the old single wire sensors.)

The idle valve comes out Saturday.

I don't understand the DME relay comments. This relay turns on the computer, so if it doesn't work, nothing works. I've never had it NOT run, so can this still be the problem? Does anyone have hard evidence this relay can be intermittent and/or not allow a clean running engine operation?

[nhromyak]

I have heard the relay connections corrode and crack causing intermittent and good 12+ volts to the computer/DME. Apparently the DMEs are sensitive to voltage and how they are regulated.

There is also some deal about the DME circuit boards power side having hair-line cracks in them as well. I suspect all of these series DMEs have been repaired by now.

When I unplug my O2 sensor it too stabilizes the idle to 850 RPMs. I notice when my car runs hotter (210+), the idle fluctuates.

I have not checked out my O2 sensor, perhaps this is indicative of a "lazy" sensor.


OK - I REREAD your original post. Mine does the SAME thing. I figured it was normal. From what I have read, the 3.2s are known for poor cold-running. I believe it was Car and Driver who originally pointed this out.

Also, mine idles from 800 - 1200 (pulses like) when it is above half-way ( 9:30 - 10:00 position) on the temp gauge. This has somewhat been resolved by changing the base IDLE. However, when it gets warmer towards the second white mark, the idle continues to pulse.

I figured this was normal too, let me know what you find out.

Good Luck!

------------------
Nick Hromyak
'85 Carrera 7 & 9 Fuchs
Havin' Fun in Sacramento

[This message has been edited by nhromyak (edited 08-09-2001).]

[This message has been edited by nhromyak (edited 08-09-2001).]

[twin plugged targa]

I removed my O2 sensor and sprayed the hell out of it with electrical cleaner, oscillation stopped!. Fact or fiction?
Did this help and why?

[Highwatash]

Just want to say thanks for the input. My 85 is also surging when warm...it sounds like a simple fix may not exist.

[Joeaksa]

Nick,

Pls find someone and switch out the idle valve to check yours! I had exactly the same problem with my 85 3.2 and fought with it for months, to have a wrench tell me about it and change it in 10 minutes. It cured the "hunting" idle immediately.

If you live in the Dallas area let me know, will take my good one off and try it on your car. Otherwise find someone in your area with a 3.2 car and try switching the valve out. Its easy to get to and if yours has 40-60K miles on it and your idle is not stable chances are its the valve.

As well, any owner of a DME car should always carry an extra FI relay! If you have one in the car, the old one senses it and will not go bad!

Joe

[nhromyak]

Joe,

I think ALL consumables know when a spare is handy and never fail. I carry an extra fuel-pump relay, the DME relay, spare belt, spare spark plugs, spare rotor and a few other "spares".

I have not had a single problem (except oscillating idle when warm-hot) with the car in the last two years. I drive it four days out of the week.

I thought if the ISV is pulsing then it is working, NO? Perhaps mine is all gummed up?

Hmmm, something to do this weekend I suppose. I do see that my air-hoses connecting to the ISV are beginning to crack. I have replaced the smaller vaccum lines, but not the big ones on the ISV.

Perhaps I can persuade a local P-mech to swap me a unit so I can test.

86ragtop,
I know if I disconnect my O2 sensor the low idle RPMs disappear, and the warm-hot idle surging stops too.

Perhaps John Walker can shed some light here for all of us?!?!???


Thanks for the info.

------------------
Nick Hromyak
'85 Carrera 7 & 9 Fuchs
Havin' Fun in Sacramento

[This message has been edited by nhromyak (edited 08-10-2001).]