Idle Control Valve test and replacement

[mikee30]

Hi all,
I am working to resolve an issue on cold startup on a 86 951 which I believe is being caused by a faulty ICV. The symptoms I have is that when my 951 is cold, it will start and immediately die. The only way I can get it to keep running is if I keep giving the car gas until it is warmed up (needle at 1/4 or higher) and it will then run on it's own. It will also run very rough until it is fully warmed up. Once the car is warm, future start ups are not an issue.
So far I have replaced some maintenance items such as DME temp sensor, DME temp sensor wire, fuel pressure regular, fuel check valve, fuel filter, plugs, air filter and cleaned the throttle body. Previous owner changed the fuel injectors and spark plug wires.
I would like to replace the ICV (or clean it), however, I have two questions. 1) Has anyone been able to remove the ICV without taking off the intake manifold? My hoses going into the icv still have the original fasteners which seem to be a pain to remove with limited space. 2) Is there a proper test procedure I can do to validate the ICV is truly the issue? I hear it clicking when the car is running....

I did notice the electrical plug to the ICV has the inner wires showing, however, none seem to be shorting out from the tests I tried. Are there any issues with splicing in a replacement connector to the existing wiring to reduce the chance of a future problem? I wasn't sure if a replacement connector would impact ICV performance.

On a different note, I did open my AFM to see if there are any grooves in the black conducting strip and there are. The groves are only at the starting point. Bending the wiper arm that moves along the conducting strip did not help.

I'm also open to other ideas on what I should be checking to resolve the problem
Thanks!
Mike

[Tom]

Hi all,
I am working to resolve an issue on cold startup on a 86 951 which I believe is being caused by a faulty ICV. The symptoms I have is that when my 951 is cold, it will start and immediately die. The only way I can get it to keep running is if I keep giving the car gas until it is warmed up (needle at 1/4 or higher) and it will then run on it's own. It will also run very rough until it is fully warmed up. Once the car is warm, future start ups are not an issue.
So far I have replaced some maintenance items such as DME temp sensor, DME temp sensor wire, fuel pressure regular, fuel check valve, fuel filter, plugs, air filter and cleaned the throttle body. Previous owner changed the fuel injectors and spark plug wires.
I would like to replace the ICV (or clean it), however, I have two questions. 1) Has anyone been able to remove the ICV without taking off the intake manifold? My hoses going into the icv still have the original fasteners which seem to be a pain to remove with limited space. 2) Is there a proper test procedure I can do to validate the ICV is truly the issue? I hear it clicking when the car is running....

I did notice the electrical plug to the ICV has the inner wires showing, however, none seem to be shorting out from the tests I tried. Are there any issues with splicing in a replacement connector to the existing wiring to reduce the chance of a future problem? I wasn't sure if a replacement connector would impact ICV performance.

I'm also open to other ideas on what I should be checking to resolve the problem
Thanks!
Mike

First off, welcome to Carpokes! You've come to the right place. I start by answering your questions, and then offer some other thoughts.

1) Has anyone ever removed the ISV without removing the intake? Some people online have claimed to do it, but I honestly don't know if/how that's even possible unless you have ET's fingers. From a practical perspective, I think it's significantly easier to remove the manifold than to attempt some laparoscopic removal with the intake in place.

2) How to test the ISV? See this video for a crude test. It if passes this test, it's very likely ok.



3) If you are seeing frayed or exposed wires in the harness, you definitely want to replace the connector (whether or not it is causing your current issues). There are no hidden risks, just a better connection. For more than you wanted to know about those connectors, see this thread:

https://carpokes.com/viewtopic.php?t=565

Having said all that, I doubt your ISV is the issue. When a car starts and dies like you are describing, it's often an air-fuel-ratio problem, caused by too much or too little fuel. The ISV doesn't not generally alter AFRs, absent leaks. Given the things you already tried, I would be inclined to test the Air Flow Meter -- including both the air flow and temp sensor. For that, see this:

viewtopic.php?t=561

I'd also be inclined to check the O2 sensor -- see if just disconnecting it when cold makes any difference.

A faulty Throttle Position Sensor can also trick the DME into running on full throttle maps, which can flood a cold car. Here is a test for that:

viewtopic.php?t=525

Also, if you have not tested the DME temp sensor harness all the way to the DME, I'd do that for sure. Here's a test for that:

viewtopic.php?t=695

Cracked solder joints in the DME or KLR, or harness faults, are always a possibility too. Could be lots of things -- the key is testing so you don't go bankrupt buying parts you don't need. Is the car bone stock? And has it just started doing this, or has is always done this while you've had it?

[notny41]

I was thinking many of the same things Tom. First thought was dme temp sensor and/or throttle position sensor.

[mikee30]

Hi all, thank you for responding and Tom, thank you for taking the time to provide the links and detailed response. The car has had the issue since purchasing it. It does have Authority chips which I was thinking of removing but a few people told me the Authority Chips usually improve idle stability....so I figured I would start elsewhere.
The dme temp sensor is new (i changed it) and when doing so I noticed the connector was shorting out. So I spiced a new connector in but do not remember checking the other end..will do that! I ran the test procedure on the TPS that is on clarkesgarage and it seems fine. I even removed it to check for oil inside the tps and there was none.
I did the AFM test procedure on clarks too and it seemed fine. When i opened it though, I did notice a wear spot in the black conductor at position zero. Hard to tell if that is the problem....
Ill read through the links again and report back.
I did try disconnecting the o2 sensor but the problem was still there. I couldnt find a test procedure for the o2 sensor other than what was on clarks website but was not comfortable doing those tests. I have a new o2 sensor as I planned to use it as a maintenance item but I believe the existing one is sitting in a stripped thread!

[Tom]

You're welcome. We try to dig deeper here on carpokes.

If your AFM has been apart, I'd be inclined to test the voltage going to pin 7 of the DME when you first start up on a cold motor. It should be about .7 volts +/-. The APE chips don't change much at idle from the stock maps, so I wouldn't be worried about those. However, the reason I asked whether it ever worked right is because the chips, AFM, injectors, and FPR all need to be in sync to work right. Lots of people add big injectors or add fuel pressure thinking they'll get more power, but in reality just make the car run rich. APE chips also came if several flavors, some programmed for 3bar of fuel pressure and others for the stock 2.5bar. If you have mismatched or unknown parts, I'd start be reverting to stock everything and see if the problem persists...

[markl951]

The control circuit for the ICV runs as soon as the DME is powered on. Easiest way to check that it's working electrically is to turn the ignition key to the run position but don't start the engine. Go around to the engine bay, reach in and touch the ICV. If you feel it vibrating, it's most likely working properly, at least electrically. The DME makes it flip back and forth at ~100Hz IIRC. It can still leak air though and you'll have to remove it to test for that.

There is no fuse for the ICV circuit. If either of the two solenoid wires in the connector short to the +12V wire in the same connector then the Darlington transistors on the DME PCB become the fuse. If you don't feel any vibration of the ICV and neither side of the solenoid is open circuit, then that might be your situation.

[cda951]

Some great advice has already been dispensed, and I agree that the idle control valve and its circuit are likely not the cause of the issue. Be sure to check for vacuum leaks!

A couple of key points to remember:

1. The idle control valve circuit can be completely eliminated by bridging pins B and C of the diagnostic connector as outlined in the factory procedure for setting the base idle. When the pins are jumped, idle speed is determined by the adjustment of the bypass screw in the throttle body. I always set the base idle a bit higher than the factory spec, closer to 1000 RPM to account for a worn idle control valve.

2. The oxygen sensor will only be a factor once the sensor is hot enough to generate a reliable voltage, which even with the heated sensor of the 951 is >30 seconds after cold engine startup, plus the DME control unit ignores O2 sensor input and doesn't enter "closed loop" mode until the engine is determined to be warmed up as determined by the NTCII input. Unplugging the O2 sensor is a great way to eliminate it as being the cause running issues with the engine fully warmed up. A surging idle as the engine warms up can also indicate an idle air/fuel mixture issue and/or a lazy oxygen sensor. I prefer to use an oscilloscope and exhaust gas analyzer for such issues, but obviously not everyone has access to such things .

[usury]

Last summer when I had the intake manifold off of my na I discovered one of the rubber hoses attached to the ICV had a nice big split. Or maybe it was the breather house for the air oil separator.

Either way, my point is you could have a non-electrical factor to contend with.

[951N911]

I made a post regarding a possible ISV issue over on my thread looking for a 944 GURU in so. cal. I don't want to repost the whole thing here but if anyone looking at this would take a read over there and give me there opinion of if my issue could possibly be the ISV or I'm just hoping it is I would appreciate it

[mikee30]

Hi all,
Just wanted to provide an update as I continue to work on the problem when I have free time.
Here is what I tried so far:
1) Starting cold engine with O2 sensor disconnected - no change
2) Starting cold engine with idle control bypassed - no change
3) Tested DME sensor and harness together per the guide provided by Tom - everything checked out. The DME frayed wires was something I did fix when I hard bought the car....so at this stage I think I can rule out the DME/DME wiring.
4) TPS testing per the the guide provided by Tom shows the TPS as working.
5) I found a doc showing some DME ECM electrical tests....went through them all and didn't find any issues. The guide states the following DME pins should have continuity when the engine is off and with ground... (pins 5,10,16,17 and 19). They all checked out ok with the exception of pin 10 and ground. Checking the schematic I don't think there should be continuity between pins 10 and ground for my car? Am I incorrect?
This is the doc: https://rennlist.com/forums/attachments ... n-test.jpg

The only remaining test I have to do is:
a) retest the AFM
b) pin 7 of the DME at startup being 0.7 per Tom (thanks again Tom!)

The AFM does have a worn out black strip when at the rest location. As mentioned before, I did try bending the arm to create a new conducting path per Clarks Garage but that did not help. It's back to where it was originally so I guess I can revisit this too.

If the AFM checks out, then is my next step swapping out the performance chips with stock chips? I don't know if the chips require a 3 or 2.5bar fuel regulator....when i replaced my fuel regulator, I put back what was in there (stock model).
Prior owner changed the fuel injectors...
Any other ideas for tests? I have not removed the intake to tackle the isv given the feedback above, but maybe there is a vacuum leak of some sort underneath the intake worth inspecting.

On a different (or maybe related note), when the car is parked/stored indoors, I smell raw fuel. Sniffing around, I believe it is coming from one of my injector seals....can the two problems be related?

I am open to any suggestions

Thanks!