Yeah, this FI is pretty basic. I read the entire FI section of the workshop manuals and I was thinking, wow, this is all that is to it? Really, it is a very fast read.

I would love to hear of your realtime readings and findings.

Finally a post that says it. Most likely culprits are VACUUM leaks, or fuel related such as a bad fpr, or fuel pump, or something similar.

I'm fairly cereain "looking" at the o2 sensor is not going to tell you much...If you cant test it, or do a temporary swap with a local pelican, in an attempt to diagnose the issue, you may be a while 'researching" the problem.
BTW, 911Chips (Steve) provided a diagram for setting base, idle by jumping pins B & C as depicted in the diagram. I think the diagram was part of his response to a "hunting or surging idle" issue, as well.
Hope this helps...

Try browsing this link...
http://forums.pelicanparts.com/porsche-911-technical-forum/606796-3-2-idles-badly-hunting.html

Finally a post that says it. Most likely culprits are VACUUM leaks, or fuel related such as a bad fpr, or fuel pump, or something similar.

I was wrong..I said 90% of the problems are air leaks...its more like 99%.

We use to pressurized the 3.2 intake with air and a gauge on one of the vacuum lines. Amazingly..the 3.2 intake will hold air pressure for a great length of time..if the engine valve train is in good shape.

Remove the AFM and make a tool....like a cut off fuel filter end or a piece of PVC end cap that can be fitted into the rubber connector between the AFM and manifold. Put an auto tire schrader valve into your new tool by drilling a hole and fitting.

Once the tool is built..snug it into the manifold and using a tire inflator..very slowly pressurize the intake. I fit a pressure gauge into a vacuum line as you do not want more than about 5 psi...any more and you risk blowing out engine seals, etc. (yes it pressurizes the intake and crankcase) You may find a bad oil cap..breather hoses and all sorts of air leaks.

It is a quick way to find/fix any air leaks. Much better than spraying WD40 or carb cleaner.

^Absolutely. We agree 100%.

Not to mention the fact that silicone will kill an O2 sensor in seconds. Should use ether if anything.

Two 3.2 911's in the past 8 yrs, both had idle hunting/surging idle issues; both were rectified with new O2 sensors. I must be in the other 1% bracket :eek:

I spent the evening chasing mine. So far found a few small leaks. So I'm definitely in the 99% bracket. Already much better.

Unfortunately I've already replaced plugs, wires, cap, rotor, coil, injectors, O2 sensors, CHT, TDC and Speed Sensors chasing the trouble which I misdiagnosed. Oh well it's getting there.

Still have some leaks at the rear of the t body but they're hard to get at and I ran out of time.

How are you chasing down your leaks?

Glad to hear you're on to something. I am in the "needs maintenance rather than fiddling" approach. I found rubber airlines were crappy (just old really) with cracks so fine you could barely see them. I also needed to reset the TB idle switch, and I had a bad ICV driver (odd problem). oh, and I had the injectors cleaned.

My ignition lines were shot - and the dist cap and rotor could have been original. It's hard to say what one thing I did made it better, but she starts up right away now and idles smoothly.

I would like to get a mech to look at it and evaluate for a more precise adjustment someday soon (using a wideband ?, etc). I think someone messed with the throttle adj because I actually had to lower it when the ICV was fixed.

And I wouldn't throw motronic under a bus, the system is elegant - it was just the sensors that got old and someone fiddled with something trying to compensate.

good luck

Ohm test the idle contact switch. If this is not working it wont idle well. Over the years people mess with the screw.
Chad

+1, found my leak with a Smoker, next PCV change :rolleyes:

No you're not, the new o2 sensors were better able to handle all the vacuum leaks. ;)

"One interesting thing was the oil cap? wow I really didn't understand that one but for giggles I loosened it took a 25 mile drive run it thru the gears 3/4 throttle to 4 grand, pulls cleanly and crisply"

- Jonny042 -

If this is really the case, then the engine is running too rich as the removal of
the oil cap has bleed air directly into the intake bypassing the AFM and leaned
the mixture.

"Most likely culprits are VACUUM leaks"

- rusnak -

More mis-information! Vacuum leaks, i.e. directly into the intake system, cause the
idle to decrease and the mixture to lean as discovered by loosening the oil cap.

Air leaks are not usually identified and resolved..in the beginning. Once the leak starts..the tech or owner will start to enrich the mixture at the AFM..which will compensate..if the leak becomes worse..and the mixture can't be run any richer..then the AFM comes off and is adjusted internally...very bad. Next steps..without repairing the air leaks ...gets expensive, O2 sensors, injectors, CHTS, ICVs, DME control units and on and on.. Now the complaints about what a poor design the system is.

Over time and in particular if the intake gaskets were leaking..some individual cylinders would be very rich and others lean..or if it is one of the hoses, the gross rich mixture may be on some pots and not others..anyway..the engine management system is badly out of spec. A new O2 sensor may settle things down..the mixture would be all over the range at idle and a new sensor might handle it better. Removing the oil filler cap may or may not be a help in diagnosis.

The smart move is to always be mindful that the hoses and gaskets are over twenty years old..check for air leaks. I use the "manifold air pressure up" method. Smoke works..even carb cleaner or ether is better than nothing (it may not find your leak unless you hit it spot on) Don't use anything with silicone..it kills O2 sensors.

Don't forget the vacuum line going forward for the power brakes too..or even the brake booster can be a problem (not often).

Vacuum air leaks....be sure and check for them prior to buying FI parts for your Porsche.

"Air leaks are not usually identified and resolved..in the beginning"

Guessing not allowed! Read closely the symptoms posted at the thread beginning.

Troubleshooting Method:

1. Disconnect the O2 sensor and leave disconnected.
2. Disconnect the idle valve and leave disconnected.
Adjust the idle using the air bleed screw on the throttle body
to about 800 RPM. Now troubleshoot w/o the effects of the DME ECM.
3. If the idle functions properly now, i.e. no stalling nor surging,
then reverse steps 1 & 2 one at a time to determine where to focus.
4. If the the idle continues with problems, then check the fuel pressure,
AFM idle mixture screw, temp sensor.

Bottom line: Remember, the troubleshooter indicates that MORE air helps resolve the problem!

I've seen so many people react to vacuum leaks by enriching the mixture, it's almost de riguer. I' d rather find and fix the leaks, which are a multi-headed dragon.

At this point, perhaps an afr gauge reading in Lambda% might be wise - to reset baseline w O2 disconnected. I forgot to mention also, time to check fuel pressure.

Yes..very true. Call it the vacuum air leak Spiral of DME Death, for those that want to work around the issue.

Hey db, a couple of follow-up questions if you don't mind:

First, once you pressurize the intake system what method(s) do you use check for leaks? Carb cleaner, soapy water, listen through a hose for hissing sound, etc? Any help/guidance on what works and what doesn't would be greatly appreciated.

Second, I'd imagine that at any given point in crank rotation at least one intake valve is partially open, requiring a continuous supply of air (kind of like a leak-down tester); has this been your experience? How did/do you address it?

Thanks in advance.

Dale

By watching your pressure gauge, conveniently plugged into a vacuum hose, see if the intake/crankcase will hold pressure. If not..start listening..the air will be escaping and sound like a hole in a tire. Turn the shop radio down..you will hear it leaking.

Modern fuel injected engines don't have the big overlap like the carburetor engines. The flap in the AFM wont meter if it is bouncing around at idle. Yes you will have some intake and exhaust valves open..it wont matter, they are not open at the same time. Modern cam timing. The intake will dump into the cylinder, which is bleeding down into the crankcase, which is charged too. If the valve train has some integrity, the test works and the intake/crankcase will hold pressure. If your oil filler cap is leaking..you can hear it.

I had a skeptic at the local BMW shop. He had a 5 series..like 88 which ran very poorly..and they had done everything..and lost a lot of time and money..and the customer was upset.

Made an adapter for the intake..put a gauge on the intake and pumped it up...no pressure..big time air leak. The tech started climbing around the engine bay..he could hear a leak..but could not find it. After several minutes..eureka..front crank seal was whistling.

He replaced the front crank seal..it had no serious external oil leak and looked ok. Did the test again and the pressure held..

The BMW ran great after getting the base CO set..he was a believer after that.

Seems he found a few leaking dip sticks and oil caps after that too..and cured several running issues on problem BMW cars.

The first step in an engine driveablity problem..right out of the fuel injection manual...check for air leaks..if you don't, your just guessing.