2000 Pontiac Grand Prix Engine stumbles, tach surges

Tiny
BIG_AL
  • MEMBER
  • 2000 PONTIAC GRAND PRIX
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 55,000 MILES
My 55,000 mi. 2000 3.8 Grand Prix stumbles quite a bit under acceleration then smoothes out and runs okay with an occasional stumble. At highway speeds the tach consistently surges about 100 RPM for a second before falling back. I've noticed it also does this at city speeds with just a flicker of tach movement. The engine speed is easily heard slightly rising and falling when this happens. Around the same time this started I noticed the antifreeze level was falling with no sign of leakage anywhere. At 44,000 miles I had transmission work performed and replaced the channel plate, torque signal valve, pressure control solenoid, and fourth clutch hub so I’m thinking it’s not the transmission. Could this be more transmission trouble or engine related? I’ve heard horror stories about GM’s pink antifreeze causing intake problems; could this be the cause of the surging tach and engine stumble? No codes show when hooked to a computer.

Any help would be greatly appreciated,

Al
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Friday, August 21st, 2009 AT 9:44 AM

1 Reply

Tiny
MMPRINCE4000
  • EXPERT
Yes the DexCool has caused a lot of problems, including intake manifold gasket failure.

I think GM has warranted them to 80,000 miles, so you may be able to have them repair it.

If not, first perform a compression test to verify head gaskets are OK, then a cooling system test to find leak.

Check engine oil, for chocolate color, which would indicate coolant in oil.
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Saturday, August 22nd, 2009 AT 10:24 AM

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