ISC problem

[92Talon251]

I just ran a Idle log on my MMCD logger a for about 6 mins. All looks to be fine except my ISC it reads 0.0%. If I wiggle the wire that it closest to the firewall, that goes into the TB the ISC jumps to abotu 2.3%. Then to about 3.0% then will fall back down to 0.0%. Is the ISC reading suposed to be at 0.0%? My past logs show it in the range of 35.5% if not higher if somthing is wrong what needs to be replaced? Thanks in advance

 

[CREEP]

At idle it should read 0 fully warmed up w/ no accessories on.

 

[steve]

At idle it should read 0 fully warmed up w/ no accessories on.

I beg to differ.

The ISC when the car is warm and idling isn't at zero steps. I forget exactly what the correct number is, but mine sits about 10 steps at idle. I think that's a little low but I haven't bothered to go reset the BISS by grounding both the timing adjust connector in the engine bay and the diagnostic mode connector on the DLC in the drivers footwell in a while.

If the ISC is at zero steps at idle it's is out of range and can't close down any more to keep the idle speed down. I usually see this in peoples cars who are trying to run something other than the hardcoded 750 RPM idle speed. They have driven the ISC closed in their attempt to raise the idle speed. The ECU will resist and close the ISC untill it can't close it any more.

When you turn the AC on the ISC will step out to keep the engine idle from dropping and when your cruising the ECU will also step the ISC out so that it can slow the shock of the throttle closing when you decelerate (dashpot emulation).

Steve

 

[92Talon251]

I will try to reset the BISS by grounding the wires in hopes I can fix this problem. I bought a TPS sensor prematurely thinking it was that. But I just recently reset the timming with a timming light to 5 deg BTDC, it was set at 7 deg. It idles a better now but I still get a reading of 0.0%. If reseting the BISS doesnt help is it safe to say it is the idle speed motor going bad? The car doesnt surge it just wont idle at 750.

 

[steve]

Checking the ISC is the easy part. Pull the connector off and measure the resistance of the coils. http://dmtalon.v8eaters.com/ISC.html

I'm not sure which wire your wiggling but if it causes changes in the way the car acts you need to fix that. I'm thinking your talking about the green IPS wire but you need to describe it better.

Keep in mind any air leaks in or after the throttle body will throw of your idle speed.

Steve

 

[92Talon251]

Checking the ISC is the easy part. Pull the connector off and measure the resistance of the coils. http://dmtalon.v8eaters.com/ISC.html

I'm not sure which wire your wiggling but if it causes changes in the way the car acts you need to fix that. I'm thinking your talking about the green IPS wire but you need to describe it better.

Keep in mind any air leaks in or after the throttle body will throw of your idle speed.

Steve

Yes I am referring the the single green wire. It is more the plug than the IPS itself. The plug is cracking and when I try to remove it, it looks like it is going ot break in half. There is severe cracking on the rubber.

 

[steve]

The rubber cover on the connector may very well crack and break. Mine is brittle and cracked too.
The IPS is a critical input to the ECU for idle and deceleration control. If the IPS doesn't close you won't ever get idle surge but you also won't get ISC doing what's it's intended to.

One interesting thing about reading the ISC steps off the logger. The ECU doesn't have any feedback on where the ISC really is. So what's reported is what the ECU things the steps are.

Steve

 

[92Talon251]

Well I got the rubber connector off with out breaking it. I took the sensor to 3 different parts stores with no luck, they couldnt even order it for me. Do you know any place the sell the IPS new besides the dealer? I have been to about 6 different websites with no luck yet?

 

[steve]

Didn't know you were trying to replace it.

It's just a mechanical contact switch that grounds the connector when the throttle closes. I've never seen or heard of one breaking from wear and tear. How did it fail?

Steve

 

[92Talon251]

Well it is just a guess I dont think it has failed at all, but I tryed 3 different ways to fix the problem. I used some electrical connection cleaner on the end of the sensor and now the ICS area reads 3.0% for like 2 mins then droped to 0.0% again. I checked for leaks with my intake leaktester found no leaks, The BISS Screw is brand new, it is 3 days old as well as the O ring around it. I adjusted the IPS till the idle was somewhat perfect I did the same with the BISS screw and reset the idle. I dont have a resistance tester to test the ISC so I just used a cammera battery on the ISC it did viberate so the motor isnt bad. Basicly I was using a Trial and error troubleshooting, and since when I wiggle the wire the ICS reading jumps up it I thought it must be a weak connection from the switch to the connector leading to a bad IPS. But it could be weak coils on the ISC motor I need to buy a resistance tester.

 

[steve]

I adjusted the IPS till the idle was somewhat perfect I did the same with the BISS screw and reset the idle.

You adjust it to where the IPS just makes continuity and then turn it in 15/16th to hold butterfly sliightly open. If the IPS grounds the top connector when the throttle is closed then the switch works and you need to make sure the wire and connectors aren't failing.

You really need to measure the ISC coil resistances. If the ISC checks out then at some point you need to look at your ECU. One of the ISC circuit traces runs under the capacitors that leak.

Steve

 

[92Talon251]

Well just got done testing the ICS each of the pins reads anywhere from 28-30 ohms so I went to check the ECU. I took it apart to find the capacitors where leaking but I didnt really smell anything funny like some people decribed a seafood or hotdog smell. The leak isnt that bad, but there is a clear hardend liquid on the board. I was going to clean it up some and replace the capacitors. I have some replacement one's here I ordered from Mach V, is it safe to use electrical connection cleaner on the main board to clean up this junk?

 

[steve]

Acetone or alcohol works. Both will remove the comformal coating and help you clean off any electrolyte leakage. Any solder that isn't shiny means the electrolyte has attacked it and may have made it porous. You need to remove the parts clean under them and resolder or the acid will continue eating away at them over time.

Steve