1998 Pontiac Grand Prix Engines Dies At An Idle

Tiny
CMIL5991
  • MEMBER
  • 1998 PONTIAC GRAND PRIX
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 80,000 MILES
The car will crank over and start but when you let off the pedal and bring the engine to an idle. The car dies. If I keep the RPM's up around 2500 the engine runs just fine. But when the pedal is released the engine dies.

And yes there is a half a tank of gas!
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Monday, November 16th, 2009 AT 2:40 AM

3 Replies

Tiny
MATHIASO
  • MEMBER
Pull code if there is engine light. That could really help.
The problem may be a weak fuel pump, problem with the IAC.
Is there engine light?
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Monday, November 16th, 2009 AT 4:21 AM
Tiny
CMIL5991
  • MEMBER
No engine light at all.
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Monday, November 16th, 2009 AT 6:30 PM
Tiny
MATHIASO
  • MEMBER
My first suspect is the IAC.
The purpose of the IAC valve is to control engine idle speed, while preventing stalls due to changes in the engine load. The IAC valve, mounted in the throttle body, controls bypass air around the throttle plate. The PCM controls engine idle speed by adjusting the position of the IAC motor pintle. The PCM pulses current to the IAC coils in small steps (counts) to extend the pintle into a passage in the throttle body to decrease air flow. The PCM reverses the current pulses to retract the pintle, increasing air flow. This method allows highly accurate control of idle speed and quick response to changes in engine load. If RPM is too low, the PCM will retract the IAC pintle, resulting in more air being bypassed around the throttle plate to increase RPM. If the RPM is too high, the PCM will extend the IAC pintle, allowing less air to be bypassed around the throttle plate, decreasing RPM.


http://www.2carpros.com/forum/automotive_pictures/46384_0900c15280217cd2_1.jpg


TESTING
Check for a poor connection at the PCM or IAC motor. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connection. Inspect for a damaged wiring harness, especially if heavy work has recently been performed (intake manifold removal, engine removal, etc.) where the throttle body has been disturbed. Inspect for a restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element or foreign objects blocking the air intake system. Inspect the throttle body. Check for objects blocking the IAC passage or throttle bore. Excessive deposits, especially on high-mileage engines, can build up in the IAC passage and on the IAC pintle. Excessive deposits can also build up on the throttle plate, so check for a sticking throttle plate.


http://www.2carpros.com/forum/automotive_pictures/46384_0900c15280217cd3_1.jpg

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Tuesday, November 17th, 2009 AT 1:15 AM

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