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Idle Adjustment after new ISV - Where to start? [86 944]

 
Old 12-30-2009, 05:34 PM
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ExitWound
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Default Idle Adjustment after new ISV - Where to start? [86 944]

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.
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Old 12-30-2009, 07:03 PM
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I set mine by having the ISV off the car, adjusting the screw until the idle valve was closed, you can either see that or judge by blowing thru, then installing back and tweaking until I got the idle up to 850-900rpm (I have a standalone so it was eary to adjust the pulse to the ISV)
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Old 12-30-2009, 08:20 PM
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Check that the TPS is closing the contacts in the idle position. This tells the DME you need idle fuel maps. If that is OK, my guess would be vacuum leak.
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Old 12-30-2009, 08:24 PM
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Yeah, I checked the TPS already. It's closing completely and opening properly.

I reallllllly don't wanna take the intake off again. It's 30 degrees out! Any other ideas on how to properly set it?
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Old 12-30-2009, 09:59 PM
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just because your TPS makes the 'click' right off the idle position doesn't mean that it's working properly. I had similar idle issues and just replaced everything...TPS, DME temp sensor, ISV and gutted all my vacuum lines and replaced with the new silicon stuff. While you have the throttle body off it's not a bad idea to grab the rebuild kit and at the very least replace the ring gasket that fits between the TB and the intake - that spot can be a big vacuum leak.

IIRC, a new TPS is about $120 - it's worth it just to replace it all and know it's done. You might want to give your wire harness to the TPS a good once-over though before buying a new one just to make sure you don't have any problems there.

There are pretty comprehensive tests to check your TPS, but I checked mine and it seemed like it was testing OK but just wasn't behaving properly in the car....put in a new one and good to go.

These cars are finniky that way...
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Old 12-30-2009, 10:36 PM
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Did you let the car warm up first before jumpering the ports? Oil temp is supposed to be 70 - 90 ░C (158 - 194 ░F) before you adjust the idle. If you bypass the ISV through the test port when the car is cold and it's 30 degrees out, it won't idle properly.
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Old 12-31-2009, 09:05 AM
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I think you have to remove the vacumn pipe from the ISV and plug the pipe before you adjust idle don't you ? otherwise the ISV valve fluctuations will give a false tacho reading . Saw an article last week but can't find it now grrrr
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Old 12-31-2009, 01:58 PM
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First thing we're going to do is measure the vacuum to make absolutely sure it's not a vacuum leak anywhere. Should happen within the next few days, depending on weather. Once we determine it's okay, we'll move on from there.
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Old 12-31-2009, 02:55 PM
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Originally Posted by ExitWound View Post
First thing we're going to do is measure the vacuum to make absolutely sure it's not a vacuum leak anywhere. Should happen within the next few days, depending on weather. Once we determine it's okay, we'll move on from there.
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.

?
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Old 12-31-2009, 03:05 PM
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*I* don't. My contact wants to rule it out anyway. He thinks it's a vacuum leak and if not, he says it's always good to know that you don't have one.

The car idles at like 2000rpm with the idle screw where it is now. Is it safe to drive? What will happen one it warms up? (it's a manual transmission)
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Old 12-31-2009, 03:36 PM
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Originally Posted by ExitWound View Post
The car idles at like 2000rpm with the idle screw where it is now. Is it safe to drive? What will happen one it warms up? (it's a manual transmission)
no idea to be honest. I assume its not running rich (blue smoke ) .Have you tried removing the power connector to the cold start valve whilst its running ?

Have you checked the whole of the inlet manifold for missing plugs etc ? I found I had inadvertently pulled one of the vacumn pipes out of a 3x way junction under the inlet out of sight. Needed real small hands to put it back.

best of luck, hope you sort it out soon.
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Old 12-31-2009, 06:15 PM
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Yeah. I've forgotten a J-boot hose before, as well as the 3-way you're talking about. I triple check those every time I pull the airbox off :-P The car doesn't seem to want to run at all with them disconnected.

Not running rich as far as I can tell. Smoke was white/grey (30F outside, probably condensation mostly from being out of commission for a week). Usually there's no smoke, but it was cold so I couldnt' tell. No reason to think it's not running right. Just idling improperly.
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Old 01-01-2010, 06:01 PM
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I took apart the intake manifold to get to the ISV again today.
  • Made sure all the hoses were on tight. the hoses are new, so no cracks.
  • New ISV tests fine across the terminals.
  • TPS tests fine at all three settings (closed, open, and WOT) on ohmmeter.
When the car is first turned on, for the first 10 seconds, the engine idles STEADY at 1800rpm. The high idle is probably the result of the fooling with the idle to get the engine to stay running without the working ISV. Then, the surging idle begins, going between 1200 and 1800 every second or two.
Clamping the ISV hose, blocking all airflow to it, solves the problem, and the idle steadies off at 1200rpm.

Thoughts?? Anything.
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Old 01-04-2010, 06:04 PM
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Cleaned the new ISV. It works with a 9V battery outside the car, but not hooked up to the wiring harness on the car. Since it pulses to power, I can't directly check the operation at the harness without an oscilloscope. The rest of the car works perfectly so I'm assuming all grounds from the DME are solid.

From positive on the harness to engine block ground, I read 8.xx Volts.
From positive on the harness to (close valve) ground, I read 0 Volts.
From positive on the harness to (open valve) ground, I read 0 Volts.

From other sources on the Motronic DME, I should be reading 10V across the harness but I'm seeing 0V. How can this be?? What's going on?

Any thoughts are welcome, please.
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Old 01-04-2010, 06:24 PM
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Originally Posted by ExitWound View Post
I got a new ISV and rebuilt the Darlington Transistors in the DME with new Radio Shack ones.
.
if you have worked on the ECU at component level I would suggest you try substituting it for one off a working car.

otherwise you need to use a NOID light or use an old analogue multimeter in order to see the pulses .

Have you cleaned all the electrical connectors and traced the voltage through the loom to the ISV?

Was there any fluctuation in rpm when you pinched the vacumn tube flat before the ISV ?

Any fluctuation would indicate that you are still getting air into the vacumn system somewhere.

Last edited by peanut; 01-04-2010 at 07:18 PM.
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