3500 Engine RPM at Idle and Coasting

Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's, Olds 98 91-96, Buick Lesabres and Park Avenue 91-96. Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.
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'TilWheelsFallOff
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Joined: Sat May 23, 2015 1:19 pm
Year and Trim: 1994 SLE

3500 Engine RPM at Idle and Coasting

Post by 'TilWheelsFallOff »

Recently, when my wife started our '94 Bonneville SLE to leave a grocery store parking lot, the engine speed immediately went to 3500 rpm and stayed there. (This was the case in both Park and Drive with her foot off the gas pedal.)

The engine rpm stayed at 3500 coasting all the way to her 2nd stop, about 1 mile away. When she started the car to leave there, the engine speed was again 3500 rpm in Park (4000 rpm in Neutral). Turning the engine off and restarting it twice made no difference.

No service engine soon light was illuminated throughout this ordeal (though it has illuminated, but intermittently, in the past few months). This is the first occurrence of excessive rpm.

The vehicle has 88,000 miles.

Fortunately, the engine started normally when leaving her 3rd and final stop, and was also fine for the 4 mile trip home.

The engine has not been started since.

Please help. :helpsmilie: Thanks.
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RJolly87
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Joined: Tue May 27, 2008 8:53 am
Year and Trim: 1993 Buick Park Avenue
1994 Buick Regal Custom
Location: Las Cruces, NM

Re: 3500 Engine RPM at Idle and Coasting

Post by RJolly87 »

I would start with the basics, make sure the throttle is closing properly, linkages are not hanging up, etc.

I would also scan codes. I had a failed TPS that would trip codes some times, but also the issue you are describing as well.

Hopefully you have access to a compatible scanner, as '94 is during the dreaded OBD 1.5 era.
~Randall~
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1993 Buick Park Avenue - 197k - Some odds and ends done - Simply won't die
1994 Buick Regal - 78k - Bone stock - Always ready for a good kicking
1990 Oldsmobile 88 - Gone to a better place
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Evan0801
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Year and Trim: White 1994 Pontiac Bonneville SE, 3800 Series 1.
Location: Fort Madison Iowa

Re: 3500 Engine RPM at Idle and Coasting

Post by Evan0801 »

Possible Idle Air Control valve sensor (IAC), or Throttle Position Sensor (TPS)
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1994 Bonneville SE - Series one. L27
1998 Bonneville SE - Series Two. L36
2001 Bonneville SSEI - Series Two. L67
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