Can someone decipher this thread?
 

I'm running down a problem with the idle, and I think it's either an intermittent or failing ICV, or a number of other things. I've removed and tested the ICV and it seems ok. It ohms properly according to Bentley. However, even though base idle is set at 880, once I remove jumper from the test port, the idle drops to 750-780. Unfortunately I don't have a spare ICV to test. I was thinking I should try to isolate and see whether it was ICV, or if some kind of signal problem from the DME.

Can someone explain how I can do the test in this thread:

http://forums.pelicanparts.com/porsche-911-technical-forum/346667-motronic-idle-surge-solution.html

Or IF I can do this test, with a Fluke 179?

What's the part number on the DME?
Be aware that the early 84-85 DMEs idle at 800RPMs not 880RPM.
If you have an older DME then even if you base set idle at 880 it will drop to 800 once you remove the jumper.

So let's start with part numbers to be sure we know what you have. Do not assume it's a 86 DME, you just never know?

I need the number starting with '911.618.111.xx'

And if the DME can be opened then the chip number would also be helpful.

Yep
 

Fair point. The number is 911.618.111.05 the chip is a SW 93 Octane Chip with Cat Delete (cat is not yet deleted).

I guess I should mention that when I initially installed the chip I had a a bounce in the idle where it would go from 800 to 1500 or so. I jumpered the test port and found my base idle had been set WAY too high, at around 1100 or so, by the previous owner or someone. Resetting base idle to around 880 removed the bounce but added a new wrinkle: when COLD, I release the clutch after moving in gear, the idle drops to 200-500 RPM before recovering. Like the car is realizing it is at idle a little late.

My guess is changing the chip over revealed some issues. I should also mention I've replaced the CHT, removed and cleaned the ICV and the AFM. Working on looking for a vacuum leak, though when I remove oil cap the car does stumble momentarily before recovering.

That DME part # 911.618.111.05 is an early DME it has idle RPM at 800RPMs.
But since you have a SW chip you need to ask SW what the RPM speed is set at.
It's a high probability that the SW chip is also still at 800RPMs but best ask.

The only way to alter the idle speed is with a chip change.

I suspect everything is working as designed at 800RPM idle speed.

Many times I've seen folks try to force idle speed by opening the air screw on the TB and they simply open the screw way to much. They assume that you can force the idle speed.

Most of my chips idle at 920RPMs and I even can set the idle speed with AC turned on to a higher RPM like 1000RPMs when AC is on. But these types of changes can only be done via a chip mod.

For a car in South FL I'd advise a higher idle speed of 920RPM and even higher when the AC is on.

Fair enough
 

I asked Steve and he says it's set at 880 :/ .

Then something is clearly wrong. If you set base idle at 880 and you pull the jumper the idle should remain at 880.

Can you borrow another good DME from another car? That would be very helpful to see if the issue is the DME. Or test that DME in another car? Or send it out for testing? Testing the DME or trying another DME is the next best step.

Fair enough
 

And in your opinion, that low idle can only be due to DME, and not a faulty ICV or Vacuum leak? I'll check with the local guys and see if someone has a good DME I can swap.

I concur, post a thread in your area. I know there are other 3.2s out there. :D

Remember, put your DME into their car, not the other way around as a safety measure for the donor car.

When I first installed Steve Wong's chip, my idle hunted to discover base idle was messed with by POs trying to mask a vacuum leak. Leak fixed, Base Idle set, purred at 880-900 RPMs :D

The issue in that other thread was a blown drive transistor and I doubt that's your issue because the DME uses 2 transistors to open close the valve and if one blows open it results in the valve either fully closed or fully open. But your valve seems to be working, you imply that while it's idling at 750-800 if you jumper the pins the idle speed goes up to 880RPMs (or the base setting). Is this correct? If so then it clearly shows that the DME can command the ICV to at least open more. This would not be possible if a transistor was blown.

You can test the ICV lines quickly with a DVM. Just measure voltage with the ICV plugged in and the key in RUN.
- First test, does the ICV hum and vibrate? It should.
- Test #2, measure voltage from center pin to an outer pin then measure the center to the other outer. Both should have some voltage reading, if one side reads 0vdc then that drive transistor is bad.

One more test process,

Bridge with the jumper and set the base idle at 1000RPMs by opening the air screw, then remove the jumper. Does the idle go down with jumper removed back to 800RPMs?

Then with jumper in place set base idle at 700RPMs or as low as possible and then remove the jumper. Does the idle go up with jumper removed?

If both those test work they indicate that the ICV and the DME are capable of recovering from high or low idle speed. These 2 tests are very easy to do and at least tell us if the ICV and DME are working at a basic level.

Thanks!
 

OK, I'll check around.

Draco I'll be looking forward to that cigar video!

Thanks

Roger that KyngFish :D

Here's more test data:

I just tested the ICV voltage in my car, here's the results:

Put ignition key in RUN but do NOT start Motor.
1 - The ICV should be humming and vibrating.
2 - with the ICV plugged in you will have 12vdc on the center pin, this is the Blue/White wire and it should always be hot 12v with key in Run.
3 - Next, measure between the Center (Blue/White) and the outer Blue wire, put the '+' lead on the center and the '-' lead on the Blue outer wire. You should have +3.7vdc
4 - Now measure to the other outer pin (Blue/Red) and you should measure 3.2vdc

If you get those results the DME is correctly powering the ICV.

Hope this test also helps.

Thanks
 

Thanks Sal,

I think both tests you mentioned are a good idea. Before my chip the base idle was already set really high, around 1100, DME was taking it somewhere around the 800 range, but not quite as low as it is now, which is why I assume I was getting the bouncing idle.

If I set it high again and it goes exactly back to 780 after removing the jumper that should tell me something.

For testing the wire. I'm assuming after I hear it buzzing, that I unplug the ICV in order to test the wires? I don't have it in front of me but I'm assuming that's the only way I can get to them.

Yes, pull the connector and test the connector's voltage readings while car is on.

You need to test it plugged in, pull back the rubber boot on the connector that will give you access to the back of the connector. Some connectors you can poke the wires from the back but some harnesses have the connectors epoxy filled and you can't get into the back of the connector. If you have a epoxy filled connector just get two sharp thin pins to poke into the wires.

You must measure voltage with the ICV connected and humming.

You also just answered my first question, with the base idle at 1100RPM and jumper connected if you remove the jumper the idle goes back down.

Next try the other test, close the air screw till you drop base idle as low as possible below 800RPMs without stalling the motor then remove the jumper. Does the idle go back up?

Draco, this won't work. The ICV needs to be plugged in so it puts a load on the driver transistors. Else you have no current and will get a false voltage reading :(

oops, old brain, my bad, please ignore KyngFish. Not sure what the heck I was thinking. :eek: