1994 Cadillac STS rough idle and stall

Tiny
MACWHEELSMIKE
  • MEMBER
  • 1994 CADILLAC STS
  • V8
  • FWD
  • AUTOMATIC
  • 190,000 MILES
I have a 1994 sts and it idles ruogh the idle will fluctuate fro 400 rpm to 1100 rpm at an idle but it is intermitant and when it goes up to 1100 rpms some times it will stall I have run the engine codes but it is only giving the code history and no current codes how do I get the current codes is it something I am doing I cant find anything on the internet I hope someone can help I am a mechanic but I dont know that much about the newer cars thanks all and any help would be greatly appreceated
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Monday, January 19th, 2009 AT 11:47 AM

3 Replies

Tiny
VOLUMEMILK
  • MEMBER
THERE IS A FEW THINGS I COULD SAY ABOUT THIS. FIRST HAVE CHECK DONE ON THE COILS AND ELECTRICAL SYSTEM. ALSO O2 SENSOR PLAY A VITAL ROLE IN THE RUNNING OF YOUR AUTO. THAT IS WHY YOU HAVE 4. CHECK THE CODES ON YOUR ON BOARD SYSTEM, EVEN THOUGH YOU MAY HAVE CHECKED THEM ON OBD CODE READER. THE LAST THING I WOULD SAY IS TO CHECK YOUR FUEL SENDING UNIT. A SHORT IN THE FUEL PUMP WILL SOME TIMES RESULT IN INTERMITANT SPURTS OF COMBUSTION. CHECK FOR CODES IN YOU HISTORY OF P0140'S P0150'S- O2 SENSORS, P0300'S MISFIRES ( IF IT IS A CERTAIN CYLINDER IT WILL READ IT, IE. P0302 MEANING CYLINDER 2.) AND LAST BUT NOT LEAST FUEL INJECTOR CLOGGED. AND FOULING OUT. CHECK CARBON ON THE PLUGS. MAN THATS ALOT BUT I'M STEERING AWAY FROM HEAD GASKET ISSUES.
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Wednesday, February 18th, 2009 AT 1:20 AM
Tiny
MISTER E
  • MEMBER
I had a similar problem with my 93 sts. It had a hard time idling in the mornings when the engine was cold (< 50 degrees F). I heard the idle speed control motor making a repeating clicking sound - usually 6 clicks- every time I started the car or turned it off. The problem stopped when I replaced the ISC motor. (Now I am trying to get the idle speed down!)
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Wednesday, April 15th, 2009 AT 3:22 PM
Tiny
FACTORYJACK
  • EXPERT
I would lean toward a possible ISC as well, your vehicle being a 94 does not have OBD II, so you won't have the 4 O2 sensors, misfire codes, or any 4-digit codes for that matter. What codes are in history, that may lead to something. There is a nose switch in the ISC motor that senses when the idle is at rest, telling the ECM it can take control of idle, in respect to things like P/S load, A/C clutch, and gear position. If this nose switch is faulty, it can either not recognize throttle at idle, or think it is at idle when it is not. This can cause high idle, or stall, respectively. You could also have faukty motor windings, or poor contacts in the unit as well.
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Thursday, April 16th, 2009 AT 10:01 PM

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