mistapickles Posted January 26, 2009 Report Share Posted January 26, 2009 For the past couple weeks my car has been getting horrible gas mileage, it shoots a little puff of smoke on start up and man o man did it run warm. Well a good friend of mine, MPGor BOOST was driving behind me on the way to the local Hot Import Nights, lol, and he said my car was blowing a constant stream of dark smoke. I thought, ISC, MAF, injectors or turbo. So this morning I go out and check out my car. No shaft play in the turbo, turbo is fine. Next I disconnect the ISC, take it for a run and whaalaa, it runs like a champ and the temperature is way down. Still had a little grey smoke when it was warming up, but it disappeared after it warmed up. I started to look for a new ISC, then began to wonder, what if it isn't the ISC but whatever sensor that controls the ISC. My question is how do I determine what is actually my problem? What are the sensors involved in controlling the ISC and how do I check to see if my ISC is functioning properly? What is being told to the computer and by what to make my car run so rich? So is it my ISC or something that controls the ISC? Link to comment Share on other sites More sharing options...
Shelby Posted January 27, 2009 Report Share Posted January 27, 2009 the ISC idle control part does absolutely nothing to or for the fuel system,,, now the nose swt portion of it can ,,it is what tells the ecu the throddle is at idle,,or the engine is in decell and turn off theinjs Link to comment Share on other sites More sharing options...
mistapickles Posted January 27, 2009 Author Report Share Posted January 27, 2009 the ISC idle control part does absolutely nothing to or for the fuel system,,, now the nose swt portion of it can ,,it is what tells the ecu the throddle is at idle,,or the engine is in decell and turn off theinjs I think you are getting the ISC, idle speed control, confused with the TPS, throttle position sensor. The ISC has a servo motor in it that touches where the throttle cable is connected, it pushes the throttle open a little to help during warm up and is supposed to pull back once the motor reaches operating temperature, sometimes when they fail they continue to press the throttle open after warm up and you get a high or varying idle. The TPS is just a sensor that senses the position of the butterfly in the throttle body for the computer as you have explained. I believe the ISC is controlled by the CTS, coolant temp sensor, but am unsure if it failing will cause the symptoms I am getting with the ISC, or if it would be rectified but unplugging the ISC. Basically I am asking somebody to help me save $45 before I go out and buy a new CTS and have to still buy a ISC if it doesn't fix the problem. Does anybody know? Pickles Link to comment Share on other sites More sharing options...
ernielist Posted January 27, 2009 Report Share Posted January 27, 2009 I think you are getting the ISC, idle speed control, confused with the TPS, throttle position sensor. The ISC has a servo motor in it that touches where the throttle cable is connected, it pushes the throttle open a little to help during warm up and is supposed to pull back once the motor reaches operating temperature, sometimes when they fail they continue to press the throttle open after warm up and you get a high or varying idle. The TPS is just a sensor that senses the position of the butterfly in the throttle body for the computer as you have explained. I believe the ISC is controlled by the CTS, coolant temp sensor, but am unsure if it failing will cause the symptoms I am getting with the ISC, or if it would be rectified but unplugging the ISC. Basically I am asking somebody to help me save $45 before I go out and buy a new CTS and have to still buy a ISC if it doesn't fix the problem. Does anybody know? Pickles Well I had a high low idle problem with mine to the point it would stall out. I disconnected my ISC and it ran like a champ. Do these cars really need the ISC since the TPS sensor handles the throttle position for the ECU? I dunno, would like to know if they do because I still have a little hesitation on accel and I was wondering if a bad ISC will do this. I have been told that the ISC does three things, its a servo motor for thorttle position, it has a motor position sensor in it and a third sensor which I forgot about. Link to comment Share on other sites More sharing options...
mistapickles Posted January 27, 2009 Author Report Share Posted January 27, 2009 Well I had a high low idle problem with mine to the point it would stall out. I disconnected my ISC and it ran like a champ. Do these cars really need the ISC since the TPS sensor handles the throttle position for the ECU? I dunno, would like to know if they do because I still have a little hesitation on accel and I was wondering if a bad ISC will do this. I have been told that the ISC does three things, its a servo motor for throttle position, it has a motor position sensor in it and a third sensor which I forgot about. You need it for cold starts, I know that's all I know it's needed for. The TPS senses throttle position only, the ISC doesn't. If your ISC is disconnected it shouldn't cause hesitation unless it is unplugged with it in the extended position. did you unplug it when the engine was cold? did you have the battery disconnected when you unplugged it? Link to comment Share on other sites More sharing options...
Indiana Posted January 27, 2009 Report Share Posted January 27, 2009 Injector clips on reversed? You have an OEM PCV valve? You using a 1G MAS? Got an oil separator? Link to comment Share on other sites More sharing options...
Hoosierquest Posted January 27, 2009 Report Share Posted January 27, 2009 What shelby was talking about above is the nose switch in the ISC. If you look back there you will se where the isc contacts the throttle there is actually a switch there. if you push it in it should kind of click. you can also check it for operation with a ohm meter. Check out the FSM at www.starquestgarage.com go to the 88 manual and readup on the fuel section. Link to comment Share on other sites More sharing options...
ernielist Posted January 27, 2009 Report Share Posted January 27, 2009 You need it for cold starts, I know that's all I know it's needed for. The TPS senses throttle position only, the ISC doesn't. If your ISC is disconnected it shouldn't cause hesitation unless it is unplugged with it in the extended position. did you unplug it when the engine was cold? did you have the battery disconnected when you unplugged it? my hesitation is dirty injectors im pretty sure. Link to comment Share on other sites More sharing options...
mistapickles Posted January 28, 2009 Author Report Share Posted January 28, 2009 Injector clips on reversed? You have an OEM PCV valve? You using a 1G MAS? Got an oil separator? Injector clips are correct oem pvc, with aftermarket inline check valves between the pvc and tb stock 89 MAS and yes, an oil sperator Link to comment Share on other sites More sharing options...
mistapickles Posted January 28, 2009 Author Report Share Posted January 28, 2009 What shelby was talking about above is the nose switch in the ISC. If you look back there you will se where the isc contacts the throttle there is actually a switch there. if you push it in it should kind of click. you can also check it for operation with a ohm meter. Check out the FSM at www.starquestgarage.com go to the 88 manual and readup on the fuel section. I will check that out. Link to comment Share on other sites More sharing options...
joey_crandall Posted January 29, 2009 Report Share Posted January 29, 2009 hey my car cycles and i disconnected the isc and it idles fin haha sweet, would disconnecting it with the battery hooked up harm anything, what about hooking it up with the motor running. Link to comment Share on other sites More sharing options...
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