On start up idles high and dosnt go down until drop it into gear hereing a big clang.When we take and select park the idle goes back up ,even after truck has been running for awhile please help.............

Sounds like it might be a vacuum leak. Hope you have better luck looking for it than you've had looking for a Chevy forum

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1989 300 SEL that mostly works, but needs TLC

Is the Check Engine light on ?
Some possible causes:
1. TPS = Throttle position sensor.
2. ACT = Air Charge Temperature Sensor.
3. IAC = Idle Air Control Valve.

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2007 C 230 Sport.

The clanking is probably a worn out universal joint on the driveshaft, or a worn out rear axle gears. All very common on these. I used to have a 95' Suburban SLT.

Try this Chevrolet/GMC truck forum for more help. This is the link to the 88-99 truck forum. Many other forums there covering ALL of the Chevrolet cars and trucks.

http://www.chevytalk.org/threads/postlist.php?Cat=0&Board=UBB70

Good luck!

Ditto.
CHEVY Forum will be more helpful

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1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified

try some carb cleaner,spray around bottom of throttle body,intake for pos broken vac hose. behind throttle body there is a nippel for brake booster made of plastic ? the intake is plastic ? crack.

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Do your backup lights work?
That would indicate the park neutral switch. this switch tells the ECM when you have selected a drive gear, and what to do with the idle control. A scan tool will show the switch function.