Fast Idle

[kdjohnson2002]

Hey there- my 01 Aurora 4.0 w/140K mi has serious idle issues. Usually, it wants to idle between 1500-1800 rpm. Sometimes it goes the other way & wants to go below 500- but the one time I blipped the throttle to try & clear out whatever, it refused to drop below 3500 rpm. I had just dropped the kids off @ school & was still waiting in line. Not going to do that again... Anyway, there aren't any error codes, cable binds & I've checked for vac leaks by spraying carb cleaner around the TB, hoses & intake. Around 100K mi I had a similar issue & found the rubber grommet connecting the TB to intake was split- it took a month to find that one- but then it would eventually generate a P0172 or P0174 indicating a lean condition as a clue. Nothing this time around so the ECM must not realize that anything is wrong. Its almost like I'm purposefully holding the throttle open a bit. As near as I can tell however, the throttle plate is against its stop; the cruise & throttle cables aren't binding anyway. I've taken the TB off & cleaned it out. The IAC valve was sooted up so I cleaned it off as well. Any ideas? Lately I've been thinking that it might be a timing issue rather than a vac issue. Thoughts?

[sall]

Sounds like IACV (Idle Air Control Valve) try cleaning it first from carbon deposits, etc. Maybe also TPS (Throttle Position Sensor).

[aurora2001tan]

if its never had a TPS sensor I would install one anyway. TPS is about 58 bucks at the dealer and it can be done by someone with some tools and skill. I agree with Sall but I would replace the TPS first.

[Marc]

Scan it again.

[kdjohnson2002]

Idano. I have a scan tool which will only occasionally give up a P0507. I replaced the TPS & IACV. Overall drivability was greatly improved with the new TPS but all that did was to highlight the fast idle issue- and by fast I mean this AM I was "idling" down the highway @ 64MPH! Then, after I exited the highway moments later, everything was normal. At this point, I'm ready to try the crank sensors just to say I did.

[sall]

With your scan tool finding P0507 I would not just go thowing parts at the car.

A P0507 DTC trouble code may be caused by one or more of the following:

* A vacuum leak CHECKED
* Leaking air intake after the throttle body CHECKED
* EGR valve leaking vacuum
* A faulty positive crankcase ventilation (PCV) valve
* Damaged/failed/dirty throttle body CHECKED
* Failed EVAP system
* Failed IAC (idle air controller) or faulty IAC circuit CHECKED

If I missed something sorry, I checked off what all I thought you have done thus far to diagnose and remedy.

I know you checked for vacuum leaks but try cleaning out the EGR and replacing the gasket. Maybe you have bad or stuck pintle/plunger?

[apostolakisl]

Replacing the PCV is a no-brainer. It only costs a couple bucks and requires no tools.

[kdjohnson2002]

Ok- I'll look at the EGR & EVAP. I did the PCV the other day. The original TSP fell apart in my hand so it was clearly bad. The shop let me return the replacement IACV since it had no impact. I was eyeing the EVAP when I did the fuel filter. Yesterday AM everything was fine until I tried to merge onto the highway- no power, no downshift, etc. I pulled over & it stalled a few times then went into some sort of limp mode with revs limited to abt 3800 or so. No error codes but I thought I was going to trash my tranny when I put it into gear. Needless to say, Rora is now officially garaged until I figure this one out.

[aurora2001tan]

Document ID # 638227
2001 Oldsmobile Aurora

--------------------------------------------------------------------------------

DTC P0507
Circuit Description
The idle air control (IAC) valve is located in the throttle body. It consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. The IAC valve motor is a 2-phase bi-polar permanent magnet stepper motor that is capable of highly accurate rotation, or movement, every time the polarity of a winding is changed. This change in polarity can be seen when observing a test lamp connected between ground or B+ and an IAC valve circuit while the PCM is attempting to change engine RPM (the test lamp will flash on or off each time the polarity is changed). The PCM does not use a physical sensor to determine IAC pintle position, but uses a predicted number of counts, one count represents one change in polarity which equals one step of the stepper motor. The PCM counts the steps it has commanded to determine IAC pintle position. The PCM uses the IAC valve to control engine idle speed. It does this by changing the pintle position In the idle air passage of the throttle body. This varies the air flow around the throttle plate when the throttle is closed. To determine the desired position of the IAC pintle at idle or during deceleration, the PCM refers to the following inputs: Engine RPM, Battery voltage, Air temperature, Engine Coolant Temperature, Throttle Position Sensor angle, Engine load, and vehicle speed. When the ignition key is turned OFF after an ignition cycle, the PCM will first seat the IAC pintle in the air bypass bore and then retract it a predetermined amount of counts to allow the proper amount of air to bypass the throttle plate for engine start-up. This procedure is known as an IAC Reset.

Conditions For Running the DTC
DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0201, P0202, P0203, P0204, P0205, P0206, P0207, P0208, P0335, P0336, P0340, P0341, P0385, P0386, P0401, P0403, P0404, P0405, P0440, P0442, P0443, P0446, P0449, P1106, P1107, P1111, P1112, P1114, P1115, P1121, P1122, P1336, P1372, P1404, or P1441 are not set.
The engine coolant temperature (ECT) is greater than -40°C (-40°F).
The intake air temperature (IAT) is greater than -18°C (-1°F).
The ignition voltage is between 10.5-16 volts.
The barometric pressure (BARO) is greater than 65 kPa.
The engine run time greater than 40 seconds.
The transmission gear state has not changed for 3 seconds.
The torque converter clutch (TCC) state has not changed in 3 seconds.
The TPS less than 1.5 percent.
The spark advance is less than 12.39 degrees.
The spark retard is greater than -13.79°.
The vehicle speed sensor (VSS) is less than 3 km/h (1.9 mph).
The above conditions are present for 3 seconds.
Conditions for Setting the DTC
The actual engine speed is 100 RPM greater than the desired engine speed.
The above enabling criteria must be met and fail the diagnostic 3 consecutive times in order to set this DTC.
Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
Conditions for Clearing the MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.
Diagnostic Aids
Inspect for the following conditions:

The correct positive crankcase ventilation (PCV) valve, and installation and operation of the PCV valve
Proper operation and installation of all air intake components
Proper installation and operation of the mass air flow sensor, if equipped
A tampered with or damaged throttle stop screw
A tampered with or damaged throttle plate, throttle shaft, throttle linkage, or Cruise Control linkage, if equipped
A skewed high TP sensor
Excessive deposits in the IAC passage or on the IAC pintle
Excessive deposits in the throttle bore or on the throttle plate
Vacuum leaks
A high or unstable idle condition could be caused by a non-IAC system problem that cannot be overcome by the IAC valve. Refer to Symptoms - Engine Controls
If the problem is intermittent, refer to Intermittent Conditions in Symptoms.
Test Description
The numbers below refer to the step numbers on the diagnostic table.

This test will determine the ability of the engine controller and IAC valve circuits to control the IAC valve.

This test will determine the ability of the PCM to provide the IAC valve circuits with a ground. On a normally operating system, the test lamp should not flash while the IAC counts are incrementing.

Step
Action
Yes
No

Schematic Reference: MAF and IAC Signals

1
Did you perform the Diagnostic System Check-Engine Controls?
Go to Step 2
Go to Diagnostic System Check - Engine Controls

2

Important
Ensure engine speed stabilizes with each commanded RPM change to determine if engine speed stays within 100 RPM of the commanded RPM.


Set the parking brake and block the drive wheels.
Install a scan tool.
Start the engine.
Turn OFF all accessories.
With the scan tool RPM control function slowly increment engine speed to 1,700 RPM, then to 600 RPM, Then to 1,700 RPM.
Exit the RPM control function.
Does the engine speed stabilize within 100 RPM of the commanded RPM during the above test?
Go to Step 3
Go to Step 4

3
Observe the Freeze Frame and/or Failure records data for this DTC.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame and/or Failure Records data that you observed.
Does the DTC reset?
Go to Step 4
Go to Diagnostic Aids

4
Turn OFF the ignition.
Disconnect the IAC valve harness connector.
Connect an J 37027-A IAC motor driver to the IAC valve.
Start the engine.
With the IAC motor driver, command the IAC valve in until near 600 RPM is reached.
With the IAC motor driver, command the IAC valve out until near 1,700 RPM is reached.
Return engine speed to desired idle as indicated on the scan tool data list.
Did the engine speed steadily decrease to near 600 RPM and steadily increase to near 1,700 RPM when the IAC valve was commanded in and out?
Go to Step 5
Go to Step 11

5
With a test lamp connected to ground, probe one of the IAC valve circuits at the IAC valve harness connector using the J 36616 Connector Test Adaptor Kit .
Start the engine.
With the IAC motor driver, command low RPM while observing a scan tool until the IAC Counts start to increment.
With the IAC motor driver, command high RPM while observing a scan tool until the IAC Counts start to increment.
While the IAC Counts are incrementing observe the test lamp.
Return engine idle speed to desired idle as indicated on the scan tool data list.
Repeat the above procedure for the other three IAC valve circuits.
Did the test lamp remain ON (never flashing) while the IAC Counts where incrementing at any of the IAC valve circuits during the above test?
Go to Step 10
Go to Step 6

6
Did the test lamp remain OFF (never flashing) while the IAC Counts where incrementing at any of the IAC valve circuits during the above test?
Go to Step 9
Go to Step 7

7
Connect a test lamp between the IAC coil A low circuit and the IAC coil A high circuit at the IAC valve harness connector using the J 36616 Connector Test Adapter Kit.
With the IAC motor driver, command low RPM while observing a scan tool until the IAC counts start to increment.
With the IAC motor driver, command high RPM while observing a scan tool until the IAC Counts start to increment.
While the IAC counts are incrementing, observe the test lamp.
Return engine idle speed to desired idle as indicated on the scan tool data list.
Repeat the above procedure with the test lamp connected between the IAC coil B low circuit and the IAC coil B high circuit at the IAC valve harness connector.
Return engine speed to the desired idle as indicated on the scan tool data list.
Did the test lamp stay illuminated (never flashing) while the IAC counts where incrementing during the above test?
Go to Step 8
Go to Step 15

8
Inspect for a poor connection at the IAC valve harness connector. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 16
Go to Diagnostic Aids

9
Turn OFF the ignition.
Disconnect the PCM harness connectors.
With a DMM, test for an open or short to ground on the IAC valve circuit where the test lamp remained off. Refer to Testing for Continuity , Testing for Short to Ground , and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 16
Go to Step 12

10
Turn ON the ignition.
With a DMM, test for a short to voltage on the IAC valve circuit where the test lamp remained illuminated. Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 16
Go to Step 12

11
Inspect for the following:

Throttle body damage and tampering
Throttle lever screw tampering (if equipped)
Vacuum leaks
Faulty, incorrectly installed PCV valve and hose. (If equipped)
Throttle shaft binding
Throttle linkage or cruise control linkage binding (If equipped)
Remove the IAC Valve. Refer to Idle Air Control (IAC) Valve Replacement .
Inspect for debris in the IAC passage.
Excessive deposits on the throttle plate.
Excessive deposits in the throttle bore.
Excessive deposits on IAC Valve pintle.
Repair any of the above conditions as necessary. Refer to the appropriate repair procedure.

Did you find and correct the condition?
Go to Step 16
Go to Step 13

12
Inspect for a poor connection at the PCM harness connectors. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 16
Go to Step 15

13
Inspect for a poor connection at the IAC Valve harness connector. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 16
Go to Step 14

14
Replace the IAC valve. Refer to Idle Air Control (IAC) Valve Replacement .

Did you complete the replacement?
Go to Step 16
--

15
Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .

Did you complete the replacement?
Go to Step 16
--

16
Use the scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC run and pass?
Go to Step 17
Go to Step 2

17
With a scan tool observe the Stored information, Capture info.

Does the scan tool display any DTCs that you have not diagnosed?
Go to Diagnostic Trouble Code (DTC) List
System OK

[aurora2001tan]

I would like to hear from the OP what the status is but this was back in April

[killroypete]

Maybe, a gasket leak between the TB and the intake? had this problem, it generated a ton of error codes. I could hear the hiss at idle if i was close enough. If the mechanic relied on the error codes, he would have changed about every sensors on the engine.

[bigbubbah3]

I just had the random 3000 RPM idle in park and about 1200-1500 idle in drive which makes the car lurch forward after letting off the brake. I changed IACV, TPS, and PCV and the idle is purring at 550 RPM. I'm fairly confident that it was the IACV causing it because after removing it the plunger was loose and seemed to have too much play to me. The last time my TPS went bad it was stalling at idle. I figured I would just change the TPS while the IACV is out of the way. It amazes me that every time I change the TPS it feels like I'm driving a different car. Different throttle response every time. I used AcDelco for all the parts. Screws were T20 for both.

[AuroraGirlFromMars]

if it was loose it couldnt retract the plunger as its a stepper motor and those indents are the steps. like a worm gear clamp with broken links