High idle/rpm

I have a 1985 firebird V6 2.8l. Lately the car has had a high idle problem. The tach will jump as hgh as 15-25.Sometimes it will idle down to the 7500rpm it's supposed to idle at. After the car is driven and the vehicle is
put in "park" the rpms jump to 25, but if you shut down the engine and restart, it's OK. Starts OK on park only when the transmission is put in park while the engine is running will the rpms jump. Any ideas on the high idle? TPS, O2??? thanx for any info.....JeffVB
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Check your info. "Sometimes it will idle down to the 7500rpm it's supposed to idle at." Do you mean 750rpm ? "The tach will jump as hgh as 15-25" is that 1500-2500rpm ?
Chuck
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Tach says RPM X1000

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If your tach reads, 10-20-30-40-50-60-70 then it is RPMx100. If it reads 1-2-3-4-5-6-7-8. then it is RPMx1000. 7,500 RPM is in excess of the mechanicals of a STOCK 2.8 V6. Charles
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Dirty fuel injectors, dirty intake, bad sensors, bad electric cooling fan sensor & relay. ISC system mulfunction. ISC= Idle Speed Controll. Charles
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