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JOHN aka Eauto
JOHN aka Eauto, The Car Guy
Category: Chevy
Satisfied Customers: 15076
Experience:  ase tech
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Have a 2003 SS with 3.8 engine. Problem is Rpms are running

Customer Question

Have a 2003 Monte Carlo SS with 3.8 engine. Problem is Rpms are running high, usually after car warms up, to the point when I'm on highway car is speeding up by itself, not showing any codes, any help??
Submitted: 1 year ago.
Category: Chevy
Expert:  JOHN aka Eauto replied 1 year ago.

does it idle normal?

Customer: replied 1 year ago.
No when problem occurs idle is high, in gear maybe 1200 - 1500 rpm when normal about 7000
Customer: replied 1 year ago.
700 I meant
Customer: replied 1 year ago.
If I put in neutral when driving Rpms will spike to 3000 no load on
Expert:  JOHN aka Eauto replied 1 year ago.

have you cleaned the throttle plate and throttle body and iac?

Customer: replied 1 year ago.
Never got adequate reply or fix
Customer: replied 1 year ago.
I checked what you advised with no luck!! Found myself something telling valve to stick open, electronics you,
Think I deserve an idea for what I paid for
Customer: replied 1 year ago.
Not gonna accept phone when you charged me already for still open problem
Expert:  JOHN aka Eauto replied 1 year ago.

these are info requests we have not finished the question.. any pending or history codes?

Customer: replied 1 year ago.
No codes, it's like IAC is being told to open and does not close, and actually opening to far ...
Expert:  JOHN aka Eauto replied 1 year ago.

it sounds like a failed iac thats why I pointed you in that direction I don't want you just to throw parts at it

Customer: replied 1 year ago.
Well I changed the IAC, it worked fine for about a week, now back to same problem, IAC is staying open, what would be telling it to??
Expert:  JOHN aka Eauto replied 1 year ago.

CIRCUIT DESCRIPTION
The engine idle speed is controlled by the idle air control (IAC) valve. The IAC valve is on the throttle body The IAC valve pintle moves in and out of an idle air passage bore to control air flow around the throttle plate. The IAC valve consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation, or of movement, called steps. The stepper motor has 2 separate windings that are called coils. Each coil is supplied current by two circuits from the powertrain control module (PCM). When the PCM changes polarity of a coil, the stepper motor moves one step. The PCM uses a predetermined number of counts to determine the IAC pintle position. Observe IAC counts with a scan tool. The IAC counts will increment up or down as the PCM attempts to change the IAC valve pintle position. An IAC Reset will occur when the ignition key is turned OFF.
First, the PCM will seat the IAC pintle in the idle air passage bore. Second, the PCM will retract the pintle a predetermined number of counts to allow for efficient engine start-up. If the engine idle speed is out of range for a calibrated period of time, an idle speed diagnostic trouble code (DTC) sets.

DIAGNOSTIC AIDS
Inspect for the following conditions:

  • High resistance in an IAC valve control circuit
  • The correct positive crankcase ventilation (PCV) valve, properly installed and proper operation of the PCV valve
  • Proper operation and installation of all air intake components
  • Proper installation and operation of the mass air flow (MAF) 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 throttle position (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 can not be overcome by the IAC valve. Refer to Symptoms -
  • If the problem is determined to be intermittent, refer to Intermittent Conditions.

TEST DESCRIPTION