Idle Stabilizer Valve - Testing

[exitwound]

To not mud up the other thread about idle, I thought I'd keep the ISV chat here.

The problem
The car idles at ~500 rpm when the air temperature is cold (<50F). Until the engine warms up (about 2-3 minutes), it's very sluggish to stay running, but VERY STABLE at that RPM. Very little lapping or swaying of the RPM which leads me to believe it's not a vacuum leak. When the car warms up, the idle is set to run at 1000-1100 rpm and does so with again no swaying. It's rock steady on the idle rpm.

Test #1: ISV Clamping
I clamped off the hose going to the ISV from the J-boot/airbox while the engine was off. I then started the car and the car idled ~500rpm. No change.

While the car was running, I took off the clamp from the hose and there was again no change in the idle speed. Still hovering around 500rpm.

Test #2: Diagnostic Bypass
While the car was still cold, running around 500rpm, I bypassed the ISV with the use of the diagnostic plug. I jumped ports 2 and 5. No change in the idle.


If the ISV was indeed being disabled by either of these methods, shouldn't I see something?

[phil823]

subscribed.. my car does the same and always has although its not as much change..i idle at 650 cold then 950-1000 warm.

mabey instead of just diagnosing, replacement would be best.

[cauzomb]

try plugging or clamping the brake booster line as well.

[John_AZ]

exitwound,
I do not know if you have seen this old thread on the ICV.

Idle Valve

GL
John_AZ

[exitwound]

John, I'd never seen that thread, having searched endlessly on this problem for a long time! How I missed it, I don't know.

I believe I have access to an oscilloscope, so that might help too. One of these coming weekends, now that classes are ending, i'll have to head on out to our garage and spend the weekend there looking at things!

I have hope again.

And Phil, I do have an ISV on the way to borrow from a friend to do a swap to see what happens.

[exitwound]

Well, to update this thread, I went out to the car today, put the starter in the ignition position and felt the ISV and I gots NOTHING. No vibration at all, which leads me to believe that something's causing it not to operate. Either it's a broken wire like in one guy's report in the super ISV thread mentioned above, or the transistors on the DME are shot like another poster. It's 30 degrees out with a wind chill of like 10, so I'm not going to tackle it any time soon.

[exitwound]

I managed to get the ISV out of the car today and first tested the resistances as per the article here: BemariM3Ex - BMW M3 E30 EXperiment + more I believe this is the same ISV system used in the 944. Other references state that the testing is the same.

I have resistance across one set of terminals but not the other two. Probably has something to do with this:





I don't think the top piece should be melted like that, do you? I am going to attempt to clean the terminals inside the cap and the contacts on the ISV to see if perhaps it's just aesthetics which are damaged.

Tests on the transistors on the DME also suggest they are blown too.

[exitwound]

And here it's all cleaned up.

Idle Valve

Update: I managed to get all three circuits to read properly now (20 Ohms, 20 Ohms, and 60 Ohms), which is definitely a step up from before where only the "close valve" circuit would operate. Now both do properly.

Update 2: It doesn't work, apparently. It's intermittant that I get a circuit on the 2 other paths.

Request Can anyone who has an extra working ISV and a Multimeter do a test for me? Can you check the resistances across pin #1 and pin #2 on the ISV? Then pins #2 and #3, then pins #1 and #3? they should ALL have resistances and not be infinite (open circuit). Thanks.

[exitwound]

I got a new ISV and rebuilt the Darlington Transistors in the DME with new Radio Shack ones. Got it all back together (in 30F weather) and it started right up, and STAYED RUNNING! I'm guessing that the new parts really fixed it.

However, because I had to mess with the idle when the ISV wasn't working to get the car to stay running, my idle speeds are now all messed up. The car idles at ~1500-2000rpm, exceptionally high of course. When I bypass the ISV via the diagnostic port and start to change the idle screw, the car ends up surging, and dying, surging and dying, surging and dying (never stalling of course).

I don't believe it's a vacuum leak. I rechecked all my lines (lindsey lines) and don't believe I've had a leak since I put them in last year.

What's the best way to figure out how to set the idle properly now? Start with the screw closed/open? Car warm? Car hot? Clark's only talks about how to approach the idle adjustment if the ISV has always been working.