MAP manifold absolute pressure sensor may be bad .
SOURCE: Fast Idle
Hello two major culprits off this is your TPS sensor wich controls the idle what you need to look at is when you start the car does the Rpm needle stay in a semi fixed position give or take a couple of lines or does it idle erratic it should be at a semi fixed if erratic it probaly is out of range you can test with a ohm meter if not autozone offers free testing on sensors The second problem wich sometimes can not be detected by a scanner and doesnt always set a hard code is your IAC motor IDLE AIR CONTROL VALVE wich is inserted internal into your throttle body on the end of this has a top shaped piece wich plugs a bore hole internaly inside if this is built up with carbon or varnish it binds internally causing higher idles, lower idles ,stalling, nostarts ,hesitation,rough idle, etc this mounts with usually to torx shaped screws also can be tested with scanner but dont rule this one out it can retract and extend register fine to the computer but bind internal with out ever setting a code goodluck please rate thanks
SOURCE: 2001 Oldsmobile Silhouette surging
sounds like the idle air control motor is sticking , not sure what engine you have 3.4 litre ?? also you can ck the throttle plate right on top where the throttle cable bracket assembly part of that bracket holds down a vaccum line that has a rubber gromnet that after time leaks causing idle surge , hope this helps
SOURCE: How to I set idle speed?
Before performing any on-vehicle adjustments to fuel or ignition systems, ensure engine mechanical condition is okay. CAUTION: When battery is disconnected, vehicle computer and memory systems may lose memory data. Drive ability problems may exist until computer systems have completed a relearn cycle.
IDLE SPEED & MIXTURE
NOTE: Idle mixture is controlled by Powertrain Control Module (PCM). Adjustment is not possible. After replacement of Idle Air Control (IAC) valve, system must be cycled as identified for PCM to properly control idle speed. If idle speed is not okay after cycling system, problem is usually caused by a dirty throttle plate or vacuum leaks. Ensure all vacuum components are functioning properly.
IDLE SPEED (4-CYLINDER)
Turn ignition on with engine off for 10 seconds. Turn ignition off for 10 seconds. Start engine and idle for 30 seconds. Slowly vary engine speed between idle and 3500 RPM 5 times. Return engine to idle. PCM will now properly control idle speed. 2.2L (Cavalier & Sunfire) & 2.4L (Alero, Cavalier, Grand Am & Sunfire) Good luck and hope this helps. If it still has the high idle problem, your going to have to buy a can if not two cans ot THROTTLE BODY CLEANER NOT CARBURATOR CLEANER. Just follow the instruction on the can and try to get the Idle Air Control Valve cleaned also which is on the sdie of the throttle body so go to town when cleaning the throttle body and then do the Idle speed relearn again. The other thing to is since your doing house cleaning, buy a MAF sensor cleaner and spray down your MAF sensor and IAT sensor also, this will help with your fuell consumption.
Good luck and keep me posted, be glad to help.
Too fast an idle speed. If an engine without
computerized idle speed control is idling too fast and refuses to
come down to a normal idle speed despite your best efforts to back off the
carburetor idle speed screw or air bypass adjustment screw (fuel injection),
air is getting past the throttle somewhere. Common leak paths include the
carburetor and throttle body gaskets, carburetor insulator spacers, intake
manifold gaskets, and of course, any of the engine's vacuum fittings, hoses and
accessories. It is even possible that leaky O-rings around the fuel injectors
are allowing air to leak past the seals. Another overlooked item can be a worn
throttle shaft and a defective idle speed speed control motor/valve stuck in
the extended (high idle speed) position/throttle position sensor. Also the
throttle plate could be binding in its bore and kinked accelerator cable,
coolant temperature sensor might not be operating properly misleading the computer
that the engine is still cold and computer throwing fuel at it raising the idle
speed.----------
Getting this possibilities checked will help.Thanks.Helpmech.
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