'87 Surging Idle

[Tippy]

There is nothing wrong with Pelican!

Arguments bring out the real information IMO!

[Lorenfb]

"As I've said before, you can try and make a point or observation without trying to discredit others in the process."

Exactly! Especially when there's no basis.

And here's where it starts:

"INCORRECT!!! He already found the idle to be unstable with the new ICV. Your test only reveals whether the DME can move the ICV in either direction of its limits."

[rusnak]

Very entertaining thread. I want to correct one thing: vacuum leaks can MOST DEFINITELY lead to surging idle. They're a multi-headed beast. You find one, and there may be others. If you can't pressurize, then the hoses and clamps can be checked by hand with a flashlight and inspection mirror. The little hose on the back of the throttle body leading to the ambient air valve, and the other little hoses are common sources. They all should have some sort of clamp on them.

[ischmitz]

This all reminds me of the scene in Planes, trains, & automobiles where they are on the snowy highway at night

[another driver is trying to alert them that they're driving on the wrong side of the highway]
Neal: He says we're going the wrong way...
Del: Oh, he's drunk. How would he know where we're going?

right before they hit the oncoming traffic.

[Flat Six]

Originally Posted by 1990c4s

this thread shows what is right with pelican. And what is wrong.

+1

[kidrock]

When it comes to a surging idle, history has shown that the issue can be caused by one or more of several problems....so by steadfastly shooting down other attempts to help diagnose these problems is really doing a disservice to the original poster, as well as the entire Pelican community.

Probably even more of a disservice than "re-post(ing) mis-information that's been factually incorrect, repeated over and over again."

The point is, is that nobody likes to be "quoted" and then told that they are "wrong" or "incorrect" in a rude and condescending manner...."over and over again".

[db_cooper]

Originally Posted by rusnak

Very entertaining thread. I want to correct one thing: vacuum leaks can MOST DEFINITELY lead to surging idle. They're a multi-headed beast. You find one, and there may be others. If you can't pressurize, then the hoses and clamps can be checked by hand with a flashlight and inspection mirror. The little hose on the back of the throttle body leading to the ambient air valve, and the other little hoses are common sources. They all should have some sort of clamp on them.

Let them have their fun..poor chap's head is spinning

$200 for an ICV..next a $750 DME..next a new $1000 harness...sometimes money will not buy happiness.

Or go to our host's DIY section and look at the test plan.

Pelican Parts: 911 Tech Info - DME Troubleshooing

[ischmitz]

Fully agreed kidrock. In my opinion anyone who is seeking information on a public forum needs to be aware of certain risks such as potential miss-information. This is the nature of the beast. It's free after all. Good internet practice is to evaluate your sources and take advice out there at your own risk.

The other factor is reputation. Interestingly enough, when you spend enough time here you'll see a repeating pattern and certain individuals seem to exhibit certain character trades both good and bad over and over again.

IMHO spending time here is the "minimum price" you should be willing to pay to be able to make a judgment call. If you also are willing to contribute to the forum by posting that is a plus. If you don't like the process go somewhere else. PERIOD

If someone is in a dilemma of having to drum up business in a public forum and at the same time does't like the general dynamics of that forum for whatever reason..... tough sh|t....either behave or shut up and leave. Stop bothering others with your attitude.

[rusnak]

Well said. And might I add, Ischmitz is probably up for a statue or something for his helpful, and CLEAR no-start contributions.

[avale]

Originally Posted by db_cooper

Let them have their fun..poor chap's head is spinning

$200 for an ICV..next a $750 DME..next a new $1000 harness...sometimes money will not buy happiness.

Or go to our host's DIY section and look at the test plan.

Pelican Parts: 911 Tech Info - DME Troubleshooing

Thanks for pointing this out. This appears to be taken from the Bentley manual (which I'm using). My original request was to come up with a order of approach based on people's experience and frequency at which the various causes happen.

[ischmitz]

Avale, I think so far you are doing good. When people try to remote-troubleshoot it is always difficult to get the exact picture. Overall you didn't throw too many parts at the issue and did the right thing.

From what we know so far the new ICV was needed and replacing the CHT is probably a good idea even though it wasn't the root cause.

The DME can be repaired and that doesn't cost 750$ unless you get scammed. I think you will come out ahead.

Look on the bright side. A shop would have maybe gotten to the solution a tad faster but also would have charged you an ICV, a DME repair or replacment and LABOR. Here you have learned a lot about the car and gotten break on total cost. That's the spirit of DIY.

If you search for "Carrera, no start" you will come up with tons of similar stories. Most initially fetch some recomendations about replacing the DME relay. I second that because they are notorious for failing and you should carry a spare. Cheap insurance against break-down and getting flatt-bedded home.

When it comes to idle issues opinions go a little further apart. But again, the usual suspects are throttle linkage, sensors, leaks, mixture, etc. A methodic approach tries to eliminate the easy ones first, before changing parts. That's were a large shop is at an advantage. They can quickly swap in a known good part to eliminate or identify items. Smaller shops or unexperienced mechanics simply change part after part and charge you.

As a DIY you typically don't have that sort of resources of many parts on hand. That makes it tougher to get the job done.

And to make matters worse some items can take down others. In case of the Motronic a miss-wired tach can take out a good Motronic and a shorted injector or ICV can do the same. That makes swapping parts from fellow Porsche owners into your car a little risky.

Ingo

[Por_sha911]

Originally Posted by db_cooper

Let them have their fun..poor chap's head is spinning
$200 for an ICV..next a $750 DME..next a new $1000 harness...sometimes money will not buy happiness.
Or go to our host's DIY section and look at the test plan.
Pelican Parts: 911 Tech Info - DME Troubleshooing

That's funny, I suggested something similar on Post #7 back on 8/4!

Originally Posted by Por_sha911

You need to diagnose the problem rather an throw a lot of money for new parts at it.
Get Bentley's Repair Manual and a multimeter and test the sensors. Have you tried to clean the ICV? Have you used some starter fluid to look for vacuum leaks? (Be careful not to use too much and set your car on fire). What is the condition of your plugs, cap, rotor, wires? A poorly tuned car will mask other problems.

[db_cooper]

Originally Posted by avale

Thanks for pointing this out. This appears to be taken from the Bentley manual (which I'm using). My original request was to come up with a order of approach based on people's experience and frequency at which the various causes happen.

The best order of approach is check the easy and obvious checks first per the book.

1. Check the grounds on the intake runner..remove and clean them
2. System voltage
3. Air leaks
4. Fuel pressure
5. CO
6. Injector voltage..you can make a LED with a resistor to see it working..works on the speed and reference sensor too. Possible fault..not likely if the grounds are good.
7. Air flow meter (air flow sensor in the book) these get tampered with because of the above faults.
8. ICV..save the $$ for last
9. Speed sensor..these usually just fail..and the engine will not run..but it is in the book..so..check it.
10. CHT sensor..usually they fail and just run rich or not at all..its in the book and easy enough.

Grounds..system voltage..air leaks..with a VOM and make certain you have no air leaks..these injection systems are very robust. They won't eat many parts with age.

The process assumes a well tuned engine..no dead spark plugs or bad fuel. You have been very thoughtful. I doubt that is an issue.

[Lorenfb]

"My original request was to come up with a order of approach based on people's experience and frequency at which the various causes happen."

You've found the problem, i.e. the bad idle valve damaged the DME ECM driver.
You proved it by the tests you performed. Don't waste any more time troubleshooting.
You can easily fix the ECM yourself by tracing pins 33/34 to the bad transistor
which you can easily buy for less than $2.00 at Radio Shack, It should take less
than 30 minutes. Once you open the ECM, most likely you'll see the damaged
transistor. If not post a picture and it will be pointed out.

So in this thread you'll learn how to repair the somewhat frequent ECM idle failure.

In this thread, Dead 911 Motronic, you can learn about ECM solder problems.

Next, will be presented a DIY repair of the common ECM timing I.C. failure.

And finally, you can learn about a DIY repair of the injector output driver which is
another DME ECM failure point as is the output injector control I.C.

So, based on the above, all Pelican members should be able to easily repair their
own DME ECM when it fails and save the expensive rebuilding charge. Now that's
what a forum should provide for its members, right.

[avale]

Originally Posted by ischmitz

Avale,

I just went through the entire thread and I haven't found an answer to the first simple question: Does the ICV vibrate when the igniton is ON but the engine isn't running? If not you have a bad ECU or harness.

Next, you can you do a couple of simple tests: Take the ICV out so you can see the internal vane.

1. Disconnect the plug from the ICV and move the vane to fully open and then connect it while the ignition is in the ON position. It should move back to about mid-position, vibrate and jerk a little once every second when you hold it in your hand.

2. Same test as above but move the vane to fully closed.

In both cases the ICV needs to move to the exact same position. If the vane snaps to one end (fully open) and doesn't vibrate you have a bad ECU or harness.

Ingo

OK, the ICV does vibrate and pulses every so often.
Test 1 above (starting from fully open position) - It moved very slightly towards the center (no where near the center though), vibrates and pulses (or jerks as you stated) once every second.
Test 2 above (starting from fully closed position) - It moved to the same position as Test 1 (a little bit closed from fully open, but no where near the center though), vibrates and pulses (or jerk as you stated) once every second

So I'm starting to question whether the ECM is bad. I recall reading somewhere that you can connect a couple of pins to remove the ECM to adjust the idle. I'm I remembering that correctly? Would that be a logical next step to see if the ICV centers itself or not? In my previous test where I was able to manually create a stable idle at 880 I set the ICV in the center of the motion. I measured across pins 33 and 34 in the ECM connector and got 41 Ohms so that is within spec and appears the harness is good there.

[1990C4S]

Originally Posted by Lorenfb

So, based on the above, all Pelican members should be able to easily repair their
own DME ECM when it fails and save the expensive rebuilding charge. Now that's
what a forum should provide for its members, right.

Absolutely right. A very good post. If all comments and replies by all users could be kept in a similar tone the forum would be a much better place. (IMO)

I respect your knowledge and opinions, but sometimes I feel some 'attitude' in your replies that seems out of place in a friendly forum.

[Lorenfb]

"So I'm starting to question whether the ECM is bad."

Well O.K., if this is the case then:

1. Pull the intake, since many still feel it's an air leak, and order a gasket
set from Pelican. Heck, the car is 25 years old and probably needs gaskets
anyway.
2. Order from Pelican all new intake hoses. Remember, those air leaks could be anywhere.
Why not, those hoses probably need replacing too.
3. Open-up the wiring harness and check all the wires. It too is 25 years
old and that insulation may be bad.
4. Buy a new fuel pressure regulator, as it may be intermittent causing the pressure
to become excessive. Yes, we know it's not related to an air leak, but what the heck.
5. Oh, and let's not forget the AFM. Lots of Pelicans like to open the cover thinking
that it's causing surging. Maybe find another AFM to buy so we can rule that out.
6. And Pelican members have been replacing the speed and reference sensors
lately, so might as well replace those too.
7. How about a valve adjustment? Let's try doing that too.
8. Don't forget to order a new idle switch, as some members have found it
to be intermittent.
9. As part of the intake hose order from Pelican, order an AFM intake boot,
i.e. You know those air leaks can be anywhere. And two new hose clamps.
They could be loosening, causing those pesty little air leaks.
10. And let's not forget to order a fuel pressure dampener, as they can stick
causing the fuel pressure to stay high after an accel and back to idle throttle
movement.
11. Oh forgot, quickly supplement the Pelican parts order by adding a throttle
body gasket (air leaks).
12. Now if it's still surging, have the throttle body shaft re-shimmed (air leaks).
Remember those old carbs (not the new 3.2 guys that are into 'performance" chips)
that had unstable idles and required throttle rebuilding. Hey, it's worth a try!

Now that should cover all that's been mentioned or not mentioned in other forum
threads that MIGHT cause a problem, as typically found in forum troubleshooting
threads. Hopefully, nothing has been left out. But rest assured we can rely
someone suggesting something as a problem source, like maybe the alternator
is overcharging causing the ECM to start surging. And there's been threads lately
on overcharging! Now there's something that could also be replaced if the
12 items above don't solve the surging, that will need replacement eventually.
And all the parts being purchased will benefit Pelican Parts in return for all
the free help received on this forum. Just think of what's being saved in labor
by not having your Porsche in a shop.

Bottom line: If all possibilities have been exhausted, maybe it's the DME ECM
and it's then time to borrow one. Don't waste money having the ECM tested,
as those rebuilders will usually find a problem whether one is there or not.
Once you confirm the problem, a DIY repair effort is in order. Surely, other
knowledgeable DME ECM experts, i.e. There must be many given some of
the DME ECM postings and/or referrals found on the forum, that will provide
DIY repair/rebuilding help to forum members. Remember, the forum is a two-way
street, everyone benefits by giving forum help, i.e. Useful help!

[dshepp806]

Originally Posted by Lorenfb

"Every 3.2 DME I worked on where one of the ICV drivers failed completely moved the ICV vane smack to one end."

Then you haven't worked on very many, as some drivers fail in the open condition,
as is the most likely case here.

"This failure can only be detected with an oscilloscope."

Not really! A simple ohm test from the collector to emitter/base will easily determine a good/bad driver.

Without question, the devices can FAIL open or closed. So, Loren is on point there. Now, to "measure" the "failure" (whatever it's state)

Equally, I'd say that I could test P/N junctions (as Loren mentioned) to verify SS integrity....no scope needed there......(however, long ago, we used to make a box that gave us the sinusoid while we looked at PN junctions.........old school,..the "curve tracer"!!!!!!!!!). Could determinejunction "integrity" (quality),..on to the NEW stuff!!!

BEST!

Doyle

[Lorenfb]

"I'd say that I could test P/N junctions"

See, it's as simple as that. We'll have all forum members trained
as electronic techs capable of a DIY DME ECM rebuild!

[avale]

I'm looking to resolve this issue AND get an education in the process, that's all. So what you are saying is that even though the ICV moved a little bit from the full open position, that this is a reflection of it failing in an open or closed state?