high idle and over heating

Asked by Jan 21, 2017 at 12:04 AM about the 2003 Pontiac Grand Prix GT

Question type: General

need some help here.
It's scary to drive this thing, need this fixed ASAP.
In Park and Neutral, my RPM goes up to 3900 and
sits there. Happens right at start up and RPMs
never go down even when engine is hot.
In Drive it goes down to 1800 and sits there.
In Drive, if I let go of the brakes - the car takes off
like a bat, due to unusually high RPM.
When I drive this car, my foot is constantly on the
BRAKES! .. not good at all.

WTH is the matter with this thing?
Is it an idle issue?
A vacuum issue?
Something else?
Please help. It now started to over heat to.

1 Answer

76,335

First thing you want to do is get the codes read. This will point you in the direction for repairs, but I suspect it is the Throttle Positioning Sensor, or the Air Idle Control Valve. Either they are unplugged, or it and the plugin are bad. Check over the engine all the plugins to make sure everything is connected, might get lucky and find something. Another problem on these is the intake manifold may be loose or bad gasket. Take a bottle of water and squirt it around the intake gasket, around the throttle body checking for air leaks. The rpm's should hesitate if there is a vacuum leak.

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