1993 Cadillac El Dorado surging idle

  • V8
  • FWD
  • 92,000 MILES
The idle in park or in gear will pulse from 8 to12 rpm I check isc motor and it is what is pulsing, is it a bad motor or should I be looking some where else. When I shut car of isc will click several times. I have jumpped motor and will retract. The trottle body is clean. Car runs like a bear has been tuned and well maintained. The service light is on and code is for cam sensor I have changed cam sensor and code has stayed on this was done well befor surge of idle.
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have the same problem?
Friday, October 8th, 2010 AT 8:31 AM

1 Reply

Does the vehicle also exhibit what is known as a sail on. When driving and let off the gas to coast, it either maintains speed or gains speed, until you start applying brake. It sounds like you may need a minimum air rate, and tps adjustment, along with an idle learn procedure. This involves some special tools/procedure, and will need a multimeter. Here is the procedure in part, it does not include TPS adjustment.

Note: This adjustment should ONLY be performed when the throttle body has been replaced or when required to do so by diagnostic procedures. Engine should be at normal operating temperature before making any adjustment.

High Idle Speed
If the engine idle speed is not within the above limits (too high), check for vacuum leaks at the throttle body, intake manifold, vacuum fittings, tees and hoses. If the minimum air setting is made with a vacuum leak present, fuel control can be adversely affected throughout all driving ranges.

Idle Adjustment Screw
The minimum idle speed screw, used to regulate the minimum idle speed of the engine is pre-adjusted at the factory. If it is necessary to adjust the minimum idle speed screw, use tool J38457 or equivalent.

Minimum Air Adjustment

Visually check all vacuum hoses for splits, leaks or cuts. Repair as needed.
Start the engine. Operate the engine until coolant temperature is greater than 95 C.
Exit Diagnostics. Select the "OFF" mode on the Climate Control Panel (CCP). Place the steering wheel in the center, straight ahead position. Transmission should be in "PARK". Disable the generator by grounding the green harness connector plug adjacent to the generator.
Check ignition timing.
Enter diagnostics and select PCM override PS03 (ISC Motor).
Press the "COOLER" button on the CCP to retract the ISC motor. This action will disengage the A/C compressor and command EGR "OFF". The CCP display will change from '50' to '00'. The ISC motor will retract slowly to a fully retracted position. Verify that the throttle lever is resting on the minimum idle speed screw. With the ISC plunger fully retracted, disconnect the ISC harness. If the engine stalled at minimum air (ISC retracted), check the throttle blades for deposits that might restrict air flow. If there are deposits, clean the throttle bores and the area behind and around the throttle plates.
With the ISC fully retracted, the plunger should not be touching the throttle lever. If contact is noted, adjust the ISC plunger (turn in) with tool J38457 so that it is not touching the throttle lever. The throttle lever must be resting on the minimum air screw. Make sure that the throttle is not being bound by the throttle, cruise, or TV cables.
Check the minimum idle speed displayed on the Driver Information Center (DIC). Use an average reading of rpm to check minimum idle rpm.
For vehicles with 0-500 odometer miles: - Minimum idle rpm should be 450-500 rpm.
For vehicles with more that 500 odometer miles: - Minimum idle rpm should be 500-550 rpm.
If the minimum idle speed is out of limits, use tool J38457 to adjust the minimum idle screw to obtain the following idle speed
For vehicles with 0-500 odometer miles: -Set Minimum idle rpm to 475 rpm.
For vehicles with more that 500 odometer miles: -Set Minimum idle rpm to 525 rpm.
NOTE: If the idle speed cannot be corrected, check that the throttle is not held off the minimum idle speed screw because of linkage or cable binding. Also, check for leaking vacuum hoses or air leaks at the throttle body or intake manifold.

Remove the generator disable ground wire. If minimum idle speed was adjusted, adjust the TPS before performing Idle Learn Procedure.
Idle Learn Procedure
Idle learn is used during coast down to compensate for loss of air flow due to throttle body deposits. If the battery is disconnected for a service procedure or any other reason, the learned value for the idle throttle angle offset is lost. The reset procedure allows the idle learn routine to seek and retain the proper throttle angle for each particular throttle body condition. This decreases the potential for stalling during coast down.

Before performing the reset procedure all service procedures must be complete, and the engine coolant temperature must be greater than 80 C. This takes about 8 minutes.


Outside air temperature is 10 C (50 F) or greater.
Start engine and allow to idle for 13 minutes.
At end of 13 minutes, enter diagnostics (engine still running).
Turn ignition 'OFF'.
Wait a minimum of 20 seconds.
Turn ignition to 'ON' (engine not running).
Enter diagnostics.
Turn ignition 'OFF'.
Wait a minimum of 20 seconds.
Turn ignition to 'ON' (engine not running).
Enter diagnostics.
Turn ignition 'OFF'.
Wait a minimum of 20 seconds.
Start engine.
Apply brakes and place transaxle in 'DRIVE' range.
Turn the Climate Control Panel (CCP) to 'OFF' and allow engine to idle for at least 1 minute.
Turn the CCP to AUTO', verify that A/C compressor engagement occurs. Allow engine to idle for at least 1 minute.
Place transaxle in 'PARK' range and turn ignition to 'OFF'.

Make sure nothing is touching or obstructing the accelerator or brake pedals during the TP SENSOR/IDLE LEARN procedure because this will prevent the PCM from performing the learn routine.
Because of the engine load differences with the A/C 'ON' versus 'OFF', TP SENSOR/IDLE LEARN must be allowed during both conditions.
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Saturday, October 9th, 2010 AT 12:13 AM

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