gbailey911

My 87 Carrera has 77K miles, new plugs, cap, rotor button, valves adjusted, cat bypass pipe, and Steve Wong chip. Once above idle it runs like a scalded dog but at idle, it maintains 850 rpms but is not smooth. If it were a carbureted type engine, I know how I would adjust the mixture to clean up the idle (it is that type of rough idle). With all of the sensors and computer control, where should I start to clean up this idle?

Thanks in advance!

Peter Zimmermann

What's the CO% set at, and how many hydrocarbons are you seeing at that setting?
Pete

Lorenfb

"and Steve Wong chip."????????????

Take the chip out & put the stock one in, so you have a "base system" to analyze from.
Most/all chips advance the timing which can result in an unstable idle.
"All bets are off" when you have a non-stock chip installed!

Most 911s, 964s, & 993s have an idle "hunt" because of the emission system of
about 25 to 75 RPMs. You need to disconnect the O2 sensor to determine if it's
the problem source.

Then check:

1. the fuel pressure
2. the temp sensor
3. the air flow meter setting (& not just the idle mxiture screw)
4. the WOT switch
5. a mis-adjusted air screw in the throttle body
6. a non-closing idle switch
7. a bad idle valve

Steve W

George - ignore Loren. There is no extra advance at idle or any change of idle mixture in any of my chips as he assumes. If it is the chip, the only way your idle could be different than your original stock chip is if your original chip was one of the early 87-24 pin chips that had idle ignition timing of 3 degrees atdc. This chip would be labeled 1267355236. Most 87s have chip number 1267355302 which idle at 3 degrees btdc, the later updated factory spec. All chips shipped for the 87s are programmed with the updated later spec, and if your car's idle speed was set based on the early chip, you will need to turn down your base idle speed, or you idle can ride high or hunt on cold start up. There is a detailed adjustment procedure online here: http://www.911chips.com/dmeconvr.htm

Other than this if your base idle mixture adjustment is off and needs adjustment, there are some simple procedures posted that can be searched, or email me for more details

-Steve

Lorenfb

The problem states: "idle not smooth" & but it doesn't state it's too high.

Like I said; "Put the original stock chip to eliminate all unknowns".

You never really know what you're putting in your DME and how the engine is affected
when you buy a performance chip, e.g. some report pinging which may be inaudible
to others and can damage an engine and becomes more pronounced in the hot
weather. Unless you're using an octane greater than 91, you're probably going
to have a pinging problem with a performance chip. Even with the higher octane
there's no guaranty that it won't ping.

There was a reason Porsche didn't "push"/max-out the DME chips used in the 3.2s,
i.e. the varying grades of fuels available in the '80s. Well, that was about 20 years ago
with better fuels than today, e.g. in 2005 the fuels are of a lesser quality with all the
additives for emissions. Result: More potential for pinging & engine damage.
The later Porsches, e.g. 964 & 993, with their knock sensors can generally "tolerate"
& compensate for the poorer fuel qualities, the 3.2s CAN'T!

Bottomline: You may never really know what's happening in your engine until it fails.

Steve W

I think we can say that about the Porsche chips YOU sell. Why don't you continue your rant on the Pelican forums - oh that's right, you got banned

scottb

I had idle problems with my 84. A mixture adjustment did the trick. Leave the chip, and take the car to your local wrench. Have him check and adjust the mixture, as needed. If that doesn't solve the problem, then it's time to look elsewhere.

Lorenfb

"I had idle problems with my 84. A mixture adjustment did the trick. Leave the chip, and take the car to your local wrench" - scottb -

Why should the mixture have to be adjusted on a stock Porsche 3.2,
unless something has been modified out of spec, a chip maybe???
It's implied by the poster that the problem occurred recently.

Let's not suggest that the Rennlist member spend money at a shop,
when the problem may have resulted from a chip modification.
The basic diagnostics need to be done first.

Again, eliminate the chip as your source of the problem first.
It's the easiest thing to check, then the 7 point list mentioned.

Steve W

Hmm, well let's see. Intake air leaks, shrinking intake manifold gaskets, a change in exhaust configuration from a cat to a premuffler and sport muffler, wear and tear on the motor over the last 18 years, and the list goes on. There's a really good book by Charles Probst called "Bosch Fuel Injection and Engine Management" that you might want to read over some day. Could learn a thing or two.

gbailey911

Thanks to all that have provided their responses so far. Like I tried to say at the beginning of the post, the rough idle is annoying at it's worst but I can live with it if I have to. At idle, it runs as if it is slightly rich, I would lean it out at idle if I had a low speed mixture screw.

Peter, you asked about the CO% and hydrocarbons, fortunately for those of us in Virginia, we don't have any emmisions testing (yet) so I don't have a clue what these readings are but would guess the hydrocarbons are high if it is running rich.

Loren, the car ran a lot worse before the performance chip with the idle searching quite a bit before. The idle has always been rough, stock or performance chip. The searching is gone, it just seams to be running rich at idle. For now, I plan to leave the chip in and can hopefully correct the problem with the chip installed, the car just runs too good above idle with the chip. How would I disconnect the O2 sensor and what would the car do differently without it connected? When I bought the car two years ago, the PO had a K&N filter in the car and someone suggested some of the K&N cleaning/filter treatment may have made it's way to the sensor and could be causing my idle problems. As recommended, I went to a paper filter and I sprayed intake cleaner into the air box and some of my idle hunt problems of past disappeared. The remainder of the hunt problems disappered with the chip. I only run 93 octane fuel in the car.

Steve, I will check the stock chip numbers this evening when I get home from work. Can you send me the procedure to adjust the idle mixture adjustment? My e-mail address is : gbailey911@***.net

scottb

Loren: My care is bone stock. No performance chips, or other mods. Adjusting the mixture solved my idle problem. Go figure...

Lorenfb

Initial post:

"it maintains 850 rpms but is not smooth." - gbailey911 -

Last post:

"The searching is gone, it just seams to be running rich at idle." - gbailey911 -

No guessing allowed! As Pete suggested, find a shop that can check the
CO at idle. It should be 1.0 to 1.5% before the CAT with the O2 sensor
disconnected. The idle CO can be easily adjusted via the mixture screw
in the air flow meter. The mixture under load (not @ idle) is not affected
by the idle mixture screw. The air flow meter must be adjusted for that.

Dave Thomas

I guess an unintended consequence of the Pelican ban is he's going to turn up more here.

Jase007

"Intake air leaks, shrinking intake manifold gaskets"

These are often common culprits on early motronic cars. I have often solved a lot of "rough" idling problems by searching / fixing air leaks and cleaning (brake clean) out the idle control valve (ICV) [edit: porsche may call it something else].
Easier to do at home before taking to a mechanic for CO adjustment. I don't know about adjusting the factory {bosch?} setting on the air flow meter. Usually a last resort after checking some of the things in Loren's list.

The Bosch Fuel Injection and engine Management book by Robert Probst is a great resource. I rec'mnd as well.


Jason

Lorenfb

"I guess an unintended consequence of the Pelican ban is he's going to turn up more here." - Dave Thomas -

As usual, inaccurate info, a "slam", and a zero contribution to the thread!

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