IT'S IDLING TO HIGH

Tiny
GREGJONES5757@YAHOO.COM
  • MEMBER
  • 1991 CADILLAC DEVILLE
  • 69,000 MILES
Would, a bad PCM, CAUSE A IDLE CONTROL PROBLEM? I HAVE A 1991 CADILLAC, AND IT'S IDLING TO HIGH AND WHEN I BARELY HIT THE GAS, IT PICKS UP SPEED ON IT'S OWN. I'VE CHANGE THE THROTTLE BODY SENSOR, IAC, AND IDLE CONTROL MOTOR. THERE'S NO LEAKS, AND I CLEANED THE
Do you
have the same problem?
Yes
No
Wednesday, October 26th, 2011 AT 11:38 PM

6 Replies

Tiny
FIXITMR
  • MEMBER
Could be vacuum leak or IAC valve problem. Your question got cut off.
Was this
answer
helpful?
Yes
No
Thursday, October 27th, 2011 AT 3:39 AM
Tiny
GREGJONES5757@YAHOO.COM
  • MEMBER
How do I check for vaccum leaks?
Was this
answer
helpful?
Yes
No
Thursday, October 27th, 2011 AT 3:49 PM
Tiny
FACTORYJACK
  • EXPERT
Binding or dirty throttle body, faulty idle speed control motor, are most common. A sail-on condition(let off gas and seems to still accelerate) can be caused when the minimum air rate, and TPS are out of adjustment, and/or the idle learn has been lost.
Was this
answer
helpful?
Yes
No
Thursday, October 27th, 2011 AT 4:30 PM
Tiny
GREGJONES5757@YAHOO.COM
  • MEMBER
I put on a brand new TBS, IAC, AND IDEL SPEED CONTROL MOTOR, must the TBS, be set first before its put on? I've clean Throttle Body. What should I do next?
Was this
answer
helpful?
Yes
No
Thursday, October 27th, 2011 AT 4:55 PM
Tiny
FACTORYJACK
  • EXPERT
In that case, you need to make adjustments. There is a specific procedure that needs to be followed, or the results will be unsatisfactory. There is going to be special tools and procedures required to perform the adjustments and idle learn. I will look and see if the info is available in ALLDATA, to copy and paste.
Was this
answer
helpful?
Yes
No
Thursday, October 27th, 2011 AT 6:27 PM
Tiny
FACTORYJACK
  • EXPERT
TPS adjustment as follows:
1991 Cadillac DeVille V8-300 4.9L
Vehicle Level Powertrain Management Fuel Delivery and Air Induction Throttle Position Sensor Adjustments

Adjustments

Turn the engine off, key on. Reenter diagnostics and select PCM/ECM override E.5.3, ISC Motor. Press the cooler button to retract the ISC motor to the minimum air setting.

Using a T-25 L-shape torx wrench, loosen the TPS screws just enough to permit the sensor to be rotated. Open the throttle and let it snap shut against the minimum air screw. Adjust the TPS so the voltage is 0.475 to 0.525 volts.
Tighten the TPS mounting screws with the sensor in the adjusted position.
Recheck the parameter to be sure the TPS voltage is 0.475 to 0.525 volts.

Minimum air rate, and idle speed adjustment:
Minimum Air Rate - Fuel Injection Only

These adjustments should be performed only when throttle body parts have been replaced or when required to do so by the TPS adjustment. The engine should be at normal operating temperature before making all adjustments.
The minimum idle speed screw used to regulate the minimum idle speed of the engine, is pre-adjusted at the factory. The speed screw is covered with a plug to discourage unnecessary adjustment. If it is necessary to adjust the minimum idle speed screw, pierce the plug with an awl and apply leverage to remove it.

PRELIMINARY CHECKS:

Perform PFI system check, refer to COMPUTERIZED ENGINE CONTROLS/DIAGNOSTIC AND TESTING PROCEDURES. If the fuel system is operating properly, proceed to step 2.
START the engine. Enter diagnostics. Select ECM/PCM data P.0.4, Coolant Temperature. Operate the engine until the coolant temperature is greater than 95 C.
Exit diagnostics. Select the OFF mode on the ECC (this will turn the A/C compressor OFF). Place the steering wheel in the center, straight ahead position. The transmission should be ion PARK.
Enter set timing mode by jumpering Pin A to Pin B of the ALDL connector. Check the timing at 10 BTDC or 6 BTDC if regular unleaded fuel is used, and adjust as necessary. Disconnect the jumper at the ALDL after the timing has been verified as correct.
Visually check all vacuum hoses for splits, leaks or cuts.
Disable the generator by grounding the green harness connector plug adjacent to the generator.
CHECKING MINIMUM IDLE SPEED

Enter diagnostics and select ECM/PCM override E.5.3 "ISC Motor".
Press the COOLER button on the ECC to retract the ISC motor. The fuel data center will display E.5.3 and 00 alternately. The ISC motor will retract slowly (about 20 seconds) to a fully retracted position. Steady spark advance is provided during retracts. Verify that the throttle lever is resting on the minimum idle speed screw. If the engine stalls at this point, go to step 11.
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 pliers or tool J 29607 or equivalent so that it is not touching the throttle lever. The throttle lever must be resting on the minimum idle air screw. Make sure the throttle is not being bound by the throttle, cruise or TV cables. Readjust or repair the cables if they are holding the throttle open.
Connect a tachometer and check the minimum idle speed. If the minimum idle speed is outside of the following limits, proceed to step 12. Use an average reading to check minimum idle rpm.
For Vehicles With 0-500 Odometer Miles: Minimum idle rpm should be 450-500 RPM.
For Vehicles With More Than 500 Odometer Miles: Minimum idle should be 500-550 RPM.
If minimum idle speed is OK, go to step 13.

If the engine stalled at minimum air (ISC fully 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 following the "Throttle Body Cleaning Procedure". Return to step 9 after cleaning the throttle body.
If Adjustment Is Required:

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

If the minimum idle speed is out of limits, adjust the minimum idle screw to obtain the following idle speed:
Vehicle Odometer 0-500 Miles: Set the minimum idle rpm to 475 RPM.
Vehicle Odometer over 500 Miles: Set the minimum idle rpm to 525 RPM.
After adjusting minimum idle speed, proceed to step 13.

TPS SETTING CHECK

With the engine running at the minimum air RPM setting, check TPS voltage using TPS jumper harness tool J 38490 or equivalent and a DVM.
If 0.45 to 0.55 volts. Go to step 16.
If less than 0.45 volts or greater than 0.55 volts. Go to step 14.
If TPS Adjustment is Required:

With the engine OFF and the ignition ON re-enter diagnostics and select PCM override E.5.3 "ISC Motor". Press the Cooler button to retract the ISC motor to the minimum air setting.
Using a T-25 "L-shape" Torx wrench or equivalent, loosen the TPS screw just enough to permit the sensor to be rotated. Open the throttle and allow the throttle lever to snap shut against the minimum air screw. Adjust the TPS so the voltage is 0.475 to 0.525 volts. Go to step 16, "Maximum ISC Extension Adjustment".
CAUTION: DO NOT use excessive force (don't pry or pound) to adjust the TPS because damage to the TPS or binding of the throttle shaft may occur. The TPS mounting screws must be loosened to perform the adjustment.

ISC MAXIMUM EXTENSION CHECK AND ADJUSTMENT

With the key ON, and the engine OFF select the ISC motor override E.5.3. Press the WARMER button on the ECC. The fuel data center should display E.5.3 and "99" alternately indicating that override function has started. The ISC will extend to the maximum extend position.
With the ISC at maximum extension the TPS voltage should be between 1.15 volts and 1.20 volts. If the TPS is not within this range, adjust the ISC plunger as follows:
TPS below 1.15 volts.
Adjust the ISC plunger out by turning the plunger counterclockwise until the TPS parameter reads 1.18 volts.
TPS above 1.20 volts.
Adjust the ISC plunger in by turning the plunger clockwise until the TPS parameter reads 1.18 volts.
Recheck the max extend setting. Press the COOLER button to retract the ISC plunger. Wait 5 seconds. Press the WARMER button and read the TPS voltage. Readjust the ISC plunger if necessary.
AFTER ALL CHECK AND ADJUSTMENTS ARE COMPLETED

While still in diagnostics turn ignition OFF. Allow approximately 20 seconds for the ISC motor to retract and perform a TPS learn routine.
Re-enter diagnostics and repeat step 19. It takes 2 cycles for a successful TPS learn to occur.
Remove the generator disable ground wire.
START the engine and check for proper ISC motor operation.

Idle speed:
Idle Speed

Start the engine and enter diagnostics. Select PCM/ECM Override E.5.3, ISC Motor.
Press the cooler button to retract the ISC motor. The fuel data center will display E.5.3 and 00 alternately. The ISC motor will slowly retract (about 20 seconds) to a fully retracted position. Steady spark advance is provided during retracts. Verify that the throttle lever is resting on the minimum idle speed screw. With ISC plunger fully retracted, disconnect ISC harness. If the engine stalls at this point, go to step 6.
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 pliers or available special tool J-29607 so that it is not touching the throttle lever. Make sure that the throttle is not being bound by the cruise, TV, or throttle cables. Readjust or repair cables if holding the throttle open.
Connect a tachometer and check the minimum idle speed. If the minimum idle speed is outside of the following limits, adjust the minimum idle speed screw to obtain the idle speed specified in MECHANICAL SPECIFICATIONS. Use an average reading of rpm to check minimum idle rpm refer to MECHANICAL SPECIFICATIONS.
If engine speed is not within the above limits, 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 the driving range.
If the engine stalled at minimum air (ISC fully retracted), check the throttle blades for deposits that might restrict air flow. If there are deposits, clean the primary throttle bore and the area behind and around the throttle plate. Return to step one after cleaning the throttle body.
ISC SOLENOID

With key on engine off, select the ISC motor override E.5.3. Press the warmer button on the ECC. The fuel data center should display E.5.3 and 99 alternately indicating that indicating that the override function has started. The ISC will extend to the maximum extended position.
With the ISC fully extended, the TPS voltage should be between 1.15 and 1.20 volts. If the TPS is not within this range, adjust the ISC Plunger as follows:
TPS below 1.15 volts.
Adjust the ISC plunger out by turning the plunger counterclockwise until the TPS parameter reads 1.18 volts.
TPS above 1.20 volts.
Adjust the ISC plunger in be turning the plunger clockwise until the TPS parameter reads 1.18 volts.
Recheck the max extend setting, press the cooler button to retract the ISC plunger, wait 5 seconds. Press the warmer button and read the TPS voltage. Readjust the ISC plunger if necessary.
*** UPDATED BY TSB #91-I-11 DATE: 10/90

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 angel offset is lost. The reset procedure allows the idle learn routine to seek and retain the proper throttle angel 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 must be running continuously for a minimum of 18 minutes on 1990 vehicles, and 13 minutes on 1991 vehicles.

Reset procedure:

Place the vehicle transmission in drive wither the brakes applied.
Place vehicle climate control in the OFF position and allow the engine to remain at IDLE for at least one minute.
Make sure the outside air temperature reading is at least 50 F. Place the vehicle climate control in the AUTO position, verify A/C clutch engagement, and allow the engine to remain at IDLE for at least one minute.
Place the3 transmission in Park and turn off the ignition.
IMPORTANT: Because of the load differences on the engine with A/C on versus A/C off, it is very important than learning be allowed under both conditions.

There is some redundancy in these procedures. But the fact remains that if all that was replaced, it needs to learn the new limits. Before it can be successful operating with these new limits, the adjustments have to be correct.
Was this
answer
helpful?
Yes
No
+1
Thursday, October 27th, 2011 AT 6:35 PM

Please login or register to post a reply.

Recommended Guides