Used to idle rough. Now won't idle at all

[cjoenck]

You can get a used airflow sensor for approx. $300 from a number of reputable Porsche dismantlers. Try dC Auto or LA Porsche Dismantler...

[bsooley]

Appreciate all the suggestions. Checked the contacts on the idle switch as per your suggests. All OK at the DME connector. I guess I'm back to the ICV. Thanks cjoenck for the tips on how to test. I'll track down a scope and try to look at it this weekend.

BTW: This is a standard 5 speed

[bsooley]

New engine code after reconnecting the DME last night. Code 1222, another idle control contact break.

Decided to test the ICV voltage based on the preocedure mentioned earlier. Disconnected the connector to the ICV and started the car. 13.4V at pin 2. Started the car, trying to keep the revs at about 700RPM. It kept stalling as the revs dropped. The last time I took my foot off the pedal, Voila, idle!!! While in idle (ugly at first but eventually stable at about 600RPM) pin 1 showed an odd looking repeating square wave (high for about 90% of the duty cycle and then a quick dip low). Duty cycle time was approx 5ms (i.e. abut 200Hz). Mind you, we were using an oscilliscope circa WW2 so the readings could be suspect.

Reconnected the connector and the car stalled immediately.

Went to friend's house who has a VW Corrado. While in idle, removed the VW's ICV connector and connected to my ICV. Snapped shut and didn't open. Disconnected mine and connected a third (known good) ICV. It hesitated for a moment and then slowly closed. Note that the VW ICV couldn't be tested in the 964 due to a 90deg bend in the VW valve inlet.

Based on this, I'm ready to spring for a new ICV. Any last comments before I pull the trigger?

[bsooley]

Received the new ICV yesterday (thanks Pelican Parts). Installed and life is grand again! Thanks to all for your invaluable assistance. Couldn't have done it without you!!

[RandyF]

I've cleaned the ICV on my 1990 C2 as discussed in this thread using brake cleaning fluid (although apparently some think this could lead to corrosion of the valve). Now my 964 maintains a reasonable idle and hasn't stalled at stop lights, etc. like it did previously. Still, ideally it would idle with a little less RPM fluctuation when I first come to a stop.

I was wondering, is there any reason it wouldn't make sense to lubricate the ICV with WD40 or some other lubricant? Would this potentially attract more dust and grunge and make things worse? Since it's a moving part, some kind of lubrication would seem to make sense.

Great thread B.T.W., it's already helped me improve my car's idle substantially.

[cjoenck]

A little WD-40 is actually a good idea. "Little" is the operative word here - don't drown it. Also, check you vacuum line connections. One time I thought I had the ICV installed correctly and the car idled horribly - one of the connection tubes did not sit correctly and leaked air. Make sure your clamps are tight and the hose is not damaged

[ischmitz]

Without knowing for sure I doubt that lubrication is a long-time solution for the ICV. I'd venture to guess that the bushing for the movable part is worn and it is time for a replacement. My guess is that oil residue in the bushing attracts dust leading gunk buildup (making the ICV less responsive) and to wear of the bushing surface. Cleaning removes the gunk and frees up the valve.

BTW, if I am not wrong WD-40 pretty much evaporates without much residue over a couple of days and won't serve as a long-term lubricant. If you want to lubricate it maybe use some light bicycle chain oil with teflon. But then there will still be the issue with the dust collecting fast.

Ingo

[RandyF]

Ingo,

I pretty much agree with you on all aspects of your message. Since my 964 now idles after cleaning, where it would drop to zero revs once it warmed up before, it seems like I'm on the right track. But since it still idles somewhat inconsistently, it seems likely that the part will continue to degrade over time and eventually die all together.

I'm a little concerned that I'll replace the part and still have some same issues, but at the Pelican Parts price of $313.75, it relatively cheap insurance for a Porsche (Bosch really) part. It would be nice if I had known good part to test against, but I'm pretty sure this ICV's on it's last legs.

[William Miller]

Having simular issues with my 3.6 transplanted into my 81.
I'm searching threads at the moment.
The workshop manual shows the basic tests, but not much on how the components actually work.

I gone back to a Bently Manual for '84-89 carerras and there is a bit more explanation. I also have the blue bosch book which taught me a lit aoit CIS, ut it's not Porsche Specific.

So is ther a way to bench test the ICV?
What should it do when the engine is running and you disconnect the electrical connection?
I thought I read somewhere that the idle should increase to something like 1500 or 1800. Mine actually drops.

I believe I have a vacuum leak causing it to lean out, because while running if i push the flap in slightly the idle smooths out. (Like lifting the plate on a CIS meter plate. I screwed in the ajustment (bipass) plug too full closed and that helped, but I think it is still running lean.

I hooked the vacuum gauge up to the port for the flapper and it was only pulling about 10", But when I pushed the flap in which made it richer it pulled between 20-25". Also pulling about 21" when above 2500 rpm.

The car runs great except for cold startup and idle.
Fuel pressure was high, but that went lower when I pulled about 20" using a hand vacuum pump on the vacuum hose that goes to the fuel pressure regulator.
With no vacuum the pressure is 4.1 bar with 20" it's more in line with spec. which i recall is like 3.6 bar.
I don't see any obvious vacuum leaks, but it sure seems like it.
Someone asked for the best method to test. How do I pressurize the intake carefully without blowing all the gaskets and seals?

Thanks!

BTW no OBD connector on the transplant although I left the wires avalible.
Could I get a standard connector at the junk yard and make a harness to the DME wires myself? It seems like one of the biggest issuesI've read is the odd round connector in a stock 964. Are there other hurdles?

[ischmitz]

For what it is worth: When I disconnect the ICV on my 3.6 the engine stall right away. The 964 ICV is a spring-loaded device. It gets only one signal with varying duty cycle to control its position.

I created my own OBD-1 diagnostics port using a LEMO connector. And I then fabricated a custom cable to connect to the hammer. Works perfect.

Ingo

[RandyF]

FYI, I finally replaced the ICV on my 90 C2, and it does idle better, although still not perfect. It seemed to take a few drives before it "optimized" for whatever reason, but it's much better than before I started working on the problem, when it would invariably stall at idle once the engine warmed up, especially if I turned the AC on.

I had already improved the situation considerably just by cleaning the old ICV with brake cleaner and spraying the insides with a bit of WD40 once the cleaner dissipated. But the new ICV gives me a little more confidence that I won't stall in the middle of an intersection while another driver takes aim...

[William Miller]

Ingo,
I've read thru a few threads and I believe (I'm not certain.) That the hammer must have a connector that can be used with various pigtails which are dependant on the car.

Do you have a picture of the connector on the hammer itself and do you know if there is a standard connector that would match it.

I would think that I could wire up a connector using your pin-out diagram in another thread. I believe you mentioned that the hammer has an 8 pin AMP connector.

Thanks for any help.

I am assuming that I could find someone in my area that has a hammer or worst case an independant shop.

[ischmitz]

Bill.

I don't have a picture handy but you are right. The connector on the hammer itself is a standard 8-pin AMP. The matching plug can be bought at Digikey: Part # 205838-1 for the housing and part # 1658542-2 for the contacts.

I used that to make my own diagnostics cable with the AMP on one side and a LEMO connector on the other. The matching LEMO socket is hard-wired into my car.

Hope that helps,
Ingo

[William Miller]

Originally Posted by ischmitz

Bill.

I don't have a picture handy but you are right. The connector on the hammer itself is a standard 8-pin AMP. The matching plug can be bought at Digikey: Part # 205838-1 for the housing and part # 1658542-2 for the contacts.

I used that to make my own diagnostics cable with the AMP on one side and a LEMO connector on the other. The matching LEMO socket is hard-wired into my car.

Hope that helps,
Ingo

Thanks!
I ordered some parts from a salvage place today including an OBD1 19 pin and OBDII socket.

Also a bad DME unit and harness side pigtail so that we can make a breakout box.

A local "DORKI" is letting me barrow his hammer next week.
I ordered some parts from Pelican to re-seal the intake so I will be able to rule out most false air.

Can you help me find anything on Mixture adjustment and the Adaptation process?

I have an idea, but I am also sometime backwards in my assumption when working on these Bosch systems.
Thanks Again!

BTW, I bought the 19pin socket because I'm thinking about getting the Durametric software and pigtail. Also if I ever don't have acess to the real hammer, I could take it to a shop.

[ischmitz]

William,

sounds you have your plans well sorted out. I actually have gotten a 19-pin socket myself but never ended up installing it. And the reason for me is that I will keep my custom cable with the car. So if I (or a future owner) ever needs to take it to a shop he will also get the cable that connects to the shop's Hammer or PST2.

Accroding to the WSM the mixture adjustment is done with the idle bypass screw on the AFM for cars WITHOUT O2 sensor. There are instructions in the WSM. You need a CO meter and adjust idle to 0.4% - 1.2% before the CAT. Any intake leak will show up and thow CO way off towards smaller numbers (lean).

Others might correct me but it is my understanding the the air bypass screw is used to suplement the total amount of air that gets into the engine through the ICV at idle. So once you change its settings the ICV will shift its average position. In other words you want to center the ICV by properly adjusting the bypass screw. The hammer will show you real-time values for the duty cycle of the ICV. If the screw is mis-adjusted the ICV might max out when trying to stabilize idle.

On cars with O2 sensor the mixture itself is a result of the O2 sensor closed loop regulation. The Motronic calculats the amount of fuel based on the O2 sensor signal. So it is my opinion that you don't really adjust the mixture itself but you adjust an offset to the ICV position so it can do its job properly.

The reason I am saying that is that there is nothing done during the adjustment procedure that would center and disable the ICV. In contrary on the 3.2 you put a jumber into a test port and effectively stop and center the ICV. Then you make adjustments. This is not the case with the 964.

Read the duty cycle of the ICV during idle with the hammer. It should be around 55% - 65%. If it is way off you have false air getting into the engine (leak) or a grossly misadjusted bypass screw.

Cheers,
Ingo

[William Miller]

I pulled the meter last week and found the adjustment screw. The cap was missing. The screw allows more or less air to bypass the flap in the air sensor.
Screwing it in closes the bypass and reduced the amount of un-metered air.
Unscrewing it allows more unmetered air which leans the mixture.

What I found was that the screw was backed out about 3 1/4 turns from all the way screwed down or closed.

I believe I'm lean because if I push the flap in momentarily the mixture richens up and idle is smoother. I then screwed the adjustment all the way in to richen up idle. It maybe helped a bit. After reading more on rennlist, I found info about "adaptation"

I want to reset the bypass screw to the base value and try the adaptation.

I think I read on the Carerra manual that when setting the co using the bypass screw you had to jump something out in a test plug to prevent the DME from making adjustments during CO adjustment.

I'm wondering if there is something simular on a 964 system.

My attempts are to get this back to factory default parameters and hopefully the hammer will help point something out.

Maybe I just need to try and figure out where the midpoint of that adjustment screw is in relation to the tube that bypasses the flap?

[ischmitz]

Some questions:

Have you checked for vacuum leaks in your intake at all?
Do you run an O2 sensor and have the proper coding plug on the DME harness? (Hammer will tell)
Is your O2 sensor good? (Hammer will tell)

As I said the screw provides a fixed amount of unmetered air and the ICV provides an adjustable amount of unmetered air on top of that. Both will affect the mixture in the same way. By adjusting the screw you shift the regulation range of the ICV by a fixed amount.

The DME adjusts spark advance and ICV opening angle (air) to keep the idle at its programmed level of 880RPM. The O2 sensor signal is used to provide the correct amount of fuel to maintain the proper A/F ratio.

[William Miller]

This weekend I will be checking top end for unmetered air and plan on replacing the rubber tubes, fuel injector o-rings, Intake seals at heads.

I also will replace the fuel pressure regulator. (It's reading high)
I have an o2 sensor on its way and have a head temp sensor ready if needed.
I'll have acess to the hammer next week and hopefully the dignostics plug in hand and installed by then.

We are on the same page with the By-pass on the Air Meter it allows unmetered air to go arround the flap in the sensor. I'm 99% sure that the way mine is plumbed, the ICV allowes "METERED" air to By pass the throttle plate, but the ECU controls the opening depending on load and other variables to keep the idle speed steady. It's my understanding that the two are seperate.

What I hope to do is to find a way to adjust the mixture without the DME doing any compensation whle I'm making the adjustment.

I think the '84-'89 Carerra has a test plug that you install a jumper that effectivly disables DME compensation during the adjustment only.
I assume the O2 sensor is unplugged while doing this.

On the 964, I don't know what, if any provision is made for this. Maybe can be done with the code plug.

There is another 3 pin connector (Black Boshe type) in the engine harness under the seat with nothing plugged into it. It is right next to the white code plug. Is this test port? My code plug HAD no jumpers which I understand is for an a no-cat car. I installed a jumper the other day to set it for a cat car. Center terminal to positive terminal.

Hoe is this connected to the O2 sensor if at all? Maybe it switches something in the DME?

The Chip in the DME is a GIAC chip. I plan on replacing it with a stock chip.
Do the aftermarket chips effect the "adaptation" mode, or is that done somewhere else in the DME?

Thanks for all the help!

[William Miller]

Here's the chip.

[ischmitz]

Bill,

you are correct, the ICV bypasses the throttle body and thus it introduces metered air into the engine.

Both connectors (white 2-pin and black 3-pin) close to the 55pin DME connector are for coding plugs. These are inputs that are read by the multiplexing A/D converter in the DME and tell the software whether to use the O2 sensor and which ignition and fuel map to use. The switch is a logic value stored in the memory of the DME. The hammer will read this and tell you what coding the DME "sees". There are multiple sets of tables stored in the EPROM addressed by pointers.

The O2-sensor itself plugs into a round 3-pin connector on the DME harness close to the firewall. You need to connect an O2-sensor when coding the DME with the 3-pin plug. Else the DME will get "angry". The wiring harness for the O2 sensor if left open will pick up ignition noise like an antenna and throw the mixture all over the place.

Aftermarket chips typically disable the region plug by "bending" all pointers in the EPROM to the same modified map set. However, the O2 sensor logic typically stays active with these chips. So you do need the 3-pin plug with the jumper to B+

Ingo