Idle Speed Control questions

Topic: Idle Speed Control questions (Read 3430 times) previous topic - next topic

Idle Speed Control questions

April 06, 2011, 09:48:37 PM

I think I'm having a problem with the ISC on an 87 Tbird with a 3.8. My understanding is that the plunger should move out when the key is moved to the 'key on' position. I've tried this with and without a self test jumper in place - the plunger doesn't move.

What I'm seeing is that I need to press the accelerator when starting the car cold. Once things warm up somewhat, the idle is better, but still a bit rough. I'm guessing the rough warm idle is related to the 31 error I received.

Can somebody tell me if this indicates a bad ISC, or suggest things I can test to try to narrow it down?

Thanks!

Idle Speed Control questions

Reply #1 – April 07, 2011, 06:01:36 PM

With the self test jumper on, the plunger should fully retract. This should leave a 7/32" gap between the plunger and the pad on the throttle linkage it pushes on.
I can't remember if it extends with the key in run, but it should be extended when you start.
Is 31 the only code you get?
You should get a KOER code 12 if it can't force fast idle.
Here is the adjustment proceedure.

Idle Speed Control questions

Reply #2 – April 07, 2011, 06:10:08 PM

I only check KOEO codes with a warm engine when I got the 31. I'll take it for a short drive then check for KOER codes. Thanks for the info!

Idle Speed Control questions

Reply #3 – April 07, 2011, 08:53:57 PM

After taking the car for a drive, I re-ran KOEO and got only the 31 again. After that, I shut the car down for about a minute, then started the motor. I didn't get any codes - the needle on my meter never moved (I stared at it for about 2 minutes). I didn't change any of the connections from the KOEO test to the KOER test. Did I do the KOER test incorrectly?

Idle Speed Control questions

Reply #4 – April 08, 2011, 01:00:59 AM

Quote from: kevbey;357456

After taking the car for a drive, I re-ran KOEO and got only the 31 again. After that, I shut the car down for about a minute, then started the motor.

When you turn the key off you should get voltage on the meter after a five second delay.

Quote

I didn't get any codes - the needle on my meter never moved (I stared at it for about 2 minutes).

When the engine first starts you should get a 3. This is the engine code for 6 cylinders. When it finishes running the tests you should at least an 11 if there are no errors. The engine RPM should change while the tests are running.

Quote

I didn't change any of the connections from the KOEO test to the KOER test. Did I do the KOER test incorrectly?

The connections are the same.

Idle Speed Control questions

Reply #5 – April 08, 2011, 01:46:37 PM

Sorry - I should have mentioned that I did have voltage when I turned off the key following the koeo. After starting the engine I didn't even get the '3', and there wasn't a change in the rpm's. Could the 31 code from the koeo be causing, or contributing to this?

Idle Speed Control questions

Reply #6 – April 08, 2011, 04:12:50 PM

Quote from: kevbey;357503

Could the 31 code from the koeo be causing, or contributing to this?

No. The 31 code is the EGR valve position sensor voltage being too low.
I can't think of any reason why it would go into test mode for KOEO but not for KOER.

When you run KOEO does the 31 read out twice, followed by a seperator pulse, and then a read out of the memory codes?

What exactly is your setup for running the self tests?

Idle Speed Control questions

Reply #7 – April 09, 2011, 10:39:11 AM

I was running the STI to a body ground, then running the STO through a voltmeter to the positive battery terminal. This is something I found on a 'Ford Fuel Injection' website.

Idle Speed Control questions

Reply #8 – April 09, 2011, 11:48:39 AM

If your car has a fuctional check engine light, all you need is a jumper. Then you can sit in the car while you do the test.

Idle Speed Control questions

Reply #9 – April 09, 2011, 04:18:08 PM

Have you noticed whether the ISC plunger has moved at all? The EEC controls it.
There is a small "pig tail" wire on the negative battery cable. This is the logic ground for the EEC. Check that it is connected.
The shop manual method for running self tests jumpers STI to Signal Return. Try that to see if it makes a differance.

Idle Speed Control questions

Reply #10 – April 09, 2011, 09:48:17 PM

I checked the EEC logic ground and found the wire was sitting on the negative terminal, but the wire was broken. Somewhere along the way, the negative cable had been replaced, and the EEC ground was clamped into the terminal. I took care of that and tried KOER again using a jumper from STI to Signal return. This time I came up with codes 12, 58, 16, and 13 (in this order). From the definitions I've seen, the 12, 13, and 16 sound like they could be related. Would the 58 indicate a bad Air Charge Temp sensor? Also, the ISC hasn't moved at all.

Idle Speed Control questions

Reply #11 – April 10, 2011, 02:06:05 AM

All of the codes are ISC related. The 58 code is the idle tracking switch is closed when it should be open. When the throttle linkage pad presses on the ISC plunger it operates the idle tracking switch.
Loosen the hold down screw and move the ISC so the plunger is not against the throttle pad.
Unplug the connector from the ISC.
The light green/white stripe and black/white stripe wires are for the idle tracking switch.
The yellow/black stripe and white/light blue stripe wires are for the ISC motor.

Probe the ISC connector pins where the idle tracking wires would go with your OHM meter. confirm you can open and close the switch by pushing on the plunger.

Probe the motor part of the ISC connector with the OHM meter. You should have continuity with resistance but I don't know how much resistance .

You can try to run the ISC motor by applying 12v across the connector pins for the motor.
Reversing the voltage polarity will reverse the direction the plunger goes.

You don't want to put voltage on the tracking switch. So only try to run the motor if you have positively identified the tracking switch pins in the connector.

Idle Speed Control questions

Reply #12 – April 10, 2011, 08:05:44 AM

This pic is from the NAPA web site.
According to a diagram in the 84 shop manual, the top two pins are the motor and the bottom two the tracking switch.
but check to make sure.

Idle Speed Control questions

Reply #13 – April 10, 2011, 04:13:11 PM

First of all, I really appreciate all the help you're giving me with this. Here's what I found this time around:

When I probe the ISC idle tracking pins, I get continuity with about zero resistance, and the switch seems to open and close when I push on the plunger.

Probing ISC motor pins, I get continuity with about zero resistance.

I was able to run the motor in and out by applying 12v to the motor pins.

I ran the plunger all the way out and started the engine. It started with a fast idle, then gradually came down when the plunger retracted with the car running . The plunger fully retracted when I shut off the key, and didn't move again when I turned the key back on.

When I ran KOER after applying 12v to fully extend the plunger, I received codes 12 and 16, and the idle gradually slowed down when the plunger retracted. Again, the plunger fully retracted when I shut off the key, and wouldn't move when I turned the key back on. Running KOER again with the plunger retracted gave me 12, 58, 16, and 13 codes.

Both times I ran the car after running the plunger all the way out, the plunger retracted and appeared to remain in contact with the throttle pad until I shut off the key.

Thanks again for all your help!

Idle Speed Control questions

Reply #14 – April 10, 2011, 08:55:29 PM

The EEC is not doing it's thing. But before we declare it broke, let's look at the ground situation some more.

Try running KOER while jumpering the STI to the body ground again. This should work.

There are two styles of negative battery cables for these cars.

On one the EEC logic ground pigtail is grounded to the car body and goes from there to the the cable harness..
On the other the pigtail goes directly into the cable harness without going the the body. These cables have a spot about a foot or so down the main cable where the insulation is stripped off. There is a clip around the bare spot that is bolted the the body.
You should have one or the other of these body ground connections.