4.9 Will Not Idle Below 2500rpm!

[HUF]

Originally Posted by skor

The new ISC did fully retract and extend. The throttle switch also worked. After retracting the ISC through the ECM override, I noticed something peculiar. The throttle cam was not on the min air screw even though the ISC plunger screw was turned in as far in as it would go.

At this point, I removed the ISC plunger screw from the new ISC plunger and compared it to the screw from the old ISC motor. The plunger screw on the new motor was significantly longer than the screw on the old ISC motor. I installed the old ISC plunger screw in the new motor, did the adjustment and idle relearn, and all is now well.

LOL Happened to me too! While adjusting new ISC motor I noticed the plunger would not go in far enough. So I unscrewed it and compared to one from old motor. It was noticably longer. I cut it off and that was it. I thought at the time the motor was not exactly for my car...

[peteski]

Ah, thanks for the explanation skor.

Now it all makes sense. When adjusting for min idle the ISC plunger is not supposed to be touching the throttle cam. But I suppose that you've done the adjustment with the old ISC and then you didn't check again after installing the new ISC.

Peteski

[skor]

Originally Posted by peteski

Ah, thanks for the explanation skor.

Now it all makes sense. When adjusting for min idle the ISC plunger is not supposed to be touching the throttle cam. But I suppose that you've done the adjustment with the old ISC and then you didn't check again after installing the new ISC.

Peteski

Try this. Use the ECM override to retract the ISC motor as far as it will go, then disconnect the ISC motor. After the ISC is disconnected from the wiring harness, apply 12 volts to the the blue wires on the ISC motor. You can get the ISC motor plunger to retract further in until it bottoms out. This is how the motor came out of the box and in was in this possition that I did the initial adjustment.

[peteski]

Interesting. IIRC, mine retracts all the way in (and it sounds like it is ratcheting). But I have 85 Eldo with a 4.1 engine. Although I'm pretty sure that the ISC is the same. But the ECM is different.

Peteski

[n2prise]

I read all these posts and I have something else to add. I have a 96 Deville with occasional idle problems. Half the time that this occurs, the air conditioning compressor goes off line and no cool air of course. I pull off the road, turn everything off. Sometimes this is all it needs. I feel like the car is running Windows XP with bugs or something. I run a diagnostic and get no codes. That is why the ISC motor thing caught my attention.

Any explanation why the AC compressor goes off at the same time the idle goes high? I have seen 3500 RPM with the transmission in neutral or park. ON the freeway, it is like the cruise control is set to 75 or 80 MPH.

I look forward to hearing any ideas.

Thanks!

[snydly402]

kdcing, do you know how to do that with the 4.5 because the book is worthless on how to do the learns tps instructions and the codes on overriding the pcm to retract the isc motor.

[kdcing]

...don't know the 4.5, however, you can probably follow the manual process to have the ISC's plunger retract. That is,

1. Start engine and get under the hood.

2. With 1 hand, open the throttle slightly to 2k engine rpm or higher. The ISC plunger should begin to retract.

3. Once the ISC is fully retracted, use your 2nd and 3rd hand to disconnect the ISC at its pigtail/connector.

The following may work to do the relearn:
1. Find the idle screw and turn out to reduce engine speed to 425rpm or less (yep, the engine will stumble and putter and just about die).

2. Disconnect the battery for some time to clear the computer memory. If I recall correctly, 30 seconds is sufficient....better yet, leave it disconnected for 5 minutes.

3. Reconnect the battery and ISC. Start the engine. Run engine in Park for 2 minutes, then in drive (w/ foot on brake) for 2 minutes.
This procedure is taken from memory and may or may not be accurate.