: 93 STS Overheated, now idles high. PLEASE HELP



animuL
02-05-04, 01:30 PM
Okay, 93 STS 4.6 Northstar, a crack in the radiator caused the engine to get really hot, about 250 degrees. I replaced the radiator and everything and the cooling system seems fine. Now, right after I replaced it I started the car up and it idled at around 2200 RPMs, I tapped the gas and it went back down. Everything seemed fine until I shut it off and started it again; it idled way up to 2200 again and this time it wouldn't go back down. I started looking up the DTCs and found a P085 as the only current PCM code. In the Cadillac manuals it says right there that an engine overheat can throw a code 85, causing the engine to run on 4 cylinders and idle high, sounded like my exact problem, so I started to follow the directions to fix it and the ISC started clicking as though it was adjusting itself. Well now I can get the thing to stop, everytime I turn the key on or off it clicks like that. I looked at it and noticed that it is pushed out further than it used to be and it is causing the high TPS angle and thus the high idle. Right now, the car still idles way high, the ISC clicks everytime I turn the key on or off, and P085 is gone but now I am seeing P080 and sometimes P027. I have cleaned the TB thoroughly so that variable has been removed.

BeelzeBob
02-05-04, 02:58 PM
Okay, 93 STS 4.6 Northstar, a crack in the radiator caused the engine to get really hot, about 250 degrees. I replaced the radiator and everything and the cooling system seems fine. Now, right after I replaced it I started the car up and it idled at around 2200 RPMs, I tapped the gas and it went back down. Everything seemed fine until I shut it off and started it again; it idled way up to 2200 again and this time it wouldn't go back down. I started looking up the DTCs and found a P085 as the only current PCM code. In the Cadillac manuals it says right there that an engine overheat can throw a code 85, causing the engine to run on 4 cylinders and idle high, sounded like my exact problem, so I started to follow the directions to fix it and the ISC started clicking as though it was adjusting itself. Well now I can get the thing to stop, everytime I turn the key on or off it clicks like that. I looked at it and noticed that it is pushed out further than it used to be and it is causing the high TPS angle and thus the high idle. Right now, the car still idles way high, the ISC clicks everytime I turn the key on or off, and P085 is gone but now I am seeing P080 and sometimes P027. I have cleaned the TB thoroughly so that variable has been removed.


If the system only got to 250 coolant then it shouldn't have gone into limp home mode and wouldn't have been running on 4 cylinders. It it ran on 4 cylinders to protect itself (you would have sensed this due to the roughness and loss of power) the system would have had to have gotten to 275 F or so.

Just to rest your mind, 250 is not "hot"....the system can run as high as 265 F before it boils over if the coolant is 50/50 and the 15 PSI cap is functioning properly. So 250 will not hurt anything. If a tank cracked then the pressure would drop rapidly and the coolant would "boil" at 250.....but no harm will be done to the engine.

The code 85 means the ISC is having to open the throttle "too far" outside the normal parameters to achieve the desired idle. Common in an overheat condition.

The 80 is the TPS "learn" procedure not complete. At key off the ISC retracts fully to allow the sytem to "see" the TPS reading at the closed bore position to "learn" what it is as reference. The code simply indicates what you are observing...that the idle speed motor did not retract to the closed bore position.

The code 27 shows an open throttle position switch. That is also called the closed throttle switch or the nose switch. It is in the idle speed control motor and is likely the source of your problem.

If you want to stop reading now, just replace the idle speed control motor. It sounds a lot like it has just failed. Possibly the extra temp combined with the miles and years and wear and tear already on it pushed it over the edge. Not a "normal" failure expected with an overheat....just a coincidence I would say but one probably brought on by the extra heat suddenly on an already worn part.

If you want to check it out futher....start the engine and let it idle. Open the hood and go to the ISC motor and depress the plunger firmly. You should feel a "click" of the detent of the closed throttle switch. Hold the throttle lever off the plunger and depress it and see if you can feel the click of the closed throttle switch. If it moves a little and clicks and the plunge does not retract then the switch contacts are dirty or failed. If the ISC motor is clicking all the time and trying to retract due to the high idle speed then the ISC motor is just shot and you will likely find the gears inside stripped from the wear and tear of miles and 11 years.

Replace the ISC motor. When you do the only real adjustment required is to retract the plunger fully and check for clearance between the plunger and the throttle lever. to do this, open the throttle slightly to get an elevated idle speed and depress the plunger of the ISC motor with your finger. You should feel the detent of the (new) closed throttle switch and the plunger will retract. Freeze it in the retracted position by disconnecting the wire connector and allow the throttle to close to the closed bore position. There should be about .030 to .060 clearance between the plunger and the throttle lever with the plunger fully retracted and the throttle sitting at the closed bore position (the engine should idle about 450-500 RPM) at closed bore. Plug the wire back in and cycle the key several times off and on and you should be all set with no codes left.

animuL
02-05-04, 05:10 PM
I just tried a brand new ISC unit and it acts the same as the old one everytime I turn the key on or off, click click click click....

elwesso
02-05-04, 05:47 PM
Maybe a relay or something like that got messed up???

animuL
02-05-04, 05:56 PM
Actually I was wrong the new ISC fixed the problem, just an odd coincidence I guess. Thanks for all your help.

BeelzeBob
02-05-04, 09:32 PM
Actually I was wrong the new ISC fixed the problem, just an odd coincidence I guess. Thanks for all your help.

Did you retract the ISC motor and adjust it like I said?? If there is too much clearance between the ISC motor plunger and the throttle lever it could still rachet causing the click click click that you mentioned. I would retract it fully and adjust the clearance to about .030 to make sure it has sufficient extension.

Even a new ISC motor would click like you describe until it had a chance to retract the first time so that the TPS reference "learning" could take place. That is probably why it clicked at first.