2005 Pontiac Grand Prix Loss of MPG and Power Until Restart

DONLEMKE

MEMBER
2005 PONTIAC GRAND PRIX
6 CYL
FWD
AUTOMATIC
75,000 MILES

My 05 Pontiac GP from the day I bought it (2yrs ago with 32000 miles on it)I have had this intermittent problem (happens once or three times a month). Almost always with a cold engine (but happens when the ambient temp is above 70F) when the engine start you can notice a fluctuating tachometer (more than normal), under light acceleration there is a noticeable stumbling, under hard acceleration you can notice a loss of power. No trouble lights have come on or codes set in the computer. To make this go away all you have to do is pull over shut off the engine and wait 10 seconds and start the engine (no more fluctuating tachometer or loss of power). When this happens the instantaneous MPG on the trip computer shows 3/4 to 1/2 of what it does when the problem is not there. Once in a while I it will start and and then stall (this is unusual) but the next crank it will be fine. I have taken it in to the dealer and to my mechanic and neither can figure it out. The dealer said they re-calibrated the crank sensor but the next day it did it again.

5 Replies

MERLIN2021

MECHANIC
17,250 POSTS

There is a tech bulletin on your TPS(throttle position sensor), here's the bulletin:
Intermittent Chuggle or Fishbite on Light Acceleration or at Highway Speeds with No Diagnostic Trouble Codes (DTCs) (Replace Throttle Position (TPS) Sensor) TECHNICAL SERVICE BULLETIN Reference Number(s): 05-06-04-058, � Date of Issue: � September 07, 2005 Related Ref Number(s): 05-06-04-058 ARTICLE BEGINNING CONDITION Some customers may comment on an intermittent chuggle or fishbite on light acceleration or at steady-state highway speeds (typically 80-105 km/h [50-65 mph]) with no PCM DTCs set. This condition may lead the technician to suspect the TCC circuit or torque converter. CAUSE This condition may be caused by intermittent operation of the Throttle Position (TPS) Sensor. CORRECTION In observed cases, the Tech 2(R) is not fast enough to consistently detect this condition during a snapshot. It is recommended to use a DVOM set to the min/max recording mode. Connect the DVOM at the TPS connector (positive lead to TPS feedback signal pin and negative lead to TPS ground pin). Duplicate this condition by driving the vehicle. If the voltage dropout (less than 0.45 v) is recorded on the DVOM, replace the TPS sensor and re-evaluate the vehicle before continuing with other driveability or transmission diagnosis. PARTS INFORMATION Parts Information WARRANTY INFORMATION For vehicles repaired under warranty, use: Warranty Information Affected Model(s): 1995-1999 Buick Riviera; 1995-2004 Buick Regal; 1995-2005 Buick LeSabre, Park Avenue; 1997-2005 Buick Century; 1995-2001 Chevrolet Lumina; 1995-2002 Chevrolet Camaro; 1995-2005 Chevrolet Monte Carlo; 2000-2005 Chevrolet Impala; 1995-1997 Oldsmobile Cutlass Supreme, Ninety Eight; 1995-1999 Oldsmobile Eighty Eight; 1998- 2002 Oldsmobile Intrigue; 1995-2002 Pontiac Firebird; 1995-2003 Pontiac Grand Prix; 1995-2005 Pontiac Bonneville; with 3800 V6 Engine (VIN K - RPO L36) Part Number Description 24504798 Sensor, Throttle Position (TPS) Labor Operation Description Labor Time J6374 Sensor, Throttle Position - Replace Use Published Labor Operation Time

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Thursday, July 29th, 2010 AT 3:14 PM

DONLEMKE

MEMBER
3 POSTS

I read the answer you provided and noticed that my car is not one of the listed ('05 Pontiac Grand Prix with 3800 engine). I called the dealer's parts department and they told me that my car has a throttle actuator (dealer part only) and no TPS. To replace this throttle actuator you also have to replace the throttle body and thus the part is over $300.

I now know that this condition will happen after the engine is warm, hot, cool, and cold. Ambient temp makes no difference. I have also had it start in the middle of an ignition cycle and I have also had it not go away after cycling the ignition.

Have any other ideas?

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Monday, August 30th, 2010 AT 4:58 AM

MERLIN2021

MECHANIC
17,250 POSTS

You may need to have a shop scan for proper ignition switch function, especially when the problem occurs. These newer cars want everything scanned, and do not give any other means of testing. GM dealers are the ones with the Tech II tool that's required.

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Monday, August 30th, 2010 AT 4:35 PM

DONLEMKE

MEMBER
3 POSTS

I took my car into the dealer complaining of this issue on three occasions while under warranty and they could find nothing. No codes set no sensor out of bounds. I have access to a Tech II tool that I can borrow and plug in when I notice it doing this, what should I look for?

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Tuesday, August 31st, 2010 AT 4:34 AM

MERLIN2021

MECHANIC
17,250 POSTS

I do not have access and wouldn't know how to examine the ignition switch, do you have the manual for the scanner? Don't forget you might try to wiggle wire harnesses to get it to replicate the problem.