Chevrolet Repair: lumina idle, coolant temperature sensor, throttle position sensor

Question
i was trying to contact you so many time before but you are all the time maxed aut .but anyway hi my name is enes im volvo mechanic i need some help on my car chevy lumina 3.1 91000 miles  i had itermittent  problem high idle  stays all the time around 2000rpm-2500rpm  sometimes it help if you cylcle the key off it goes to normal but it comes back to high idle .no dtc in car so i replace the idle air control valve it was good for 1 day than it came back again so know it is intermitten problem it run's good 4-5 day's than just when you drive the idle stays high or when you start the stays high until it stops 2-3 days. maybe it is the coolant sensor i thing or the pcm  or what do tyou thing to check thank you

Answer
Hello Enes,
First thing I would check for is a vacuum leak. The EGR valve could be sticking, which would be a leak to the engine.
If the O2 sensor reads lean, which that would do, then the ECM would try to richen the mix, and there you are.

That is just one possibility.
The Throttle position sensor could be bad, but not set a code.

I did a search, and came up with the following, which may or may not help.

SYSTEM OR COMPONENT TO CHECK ACTION
COMPUTER INPUTS/OUTPUTS CHECK: ^ OXYGEN SENSOR (O2) - Inspect sensor for

silicon contamination from fuel, or use of
improper RTV sealant. The sensor will have
a white, powdery coating, and will result
in a high but false signal voltage (rich
exhaust indication). The ECM/PCM will then
reduce the amount of fuel delivered to the
engine, causing a severe driveability
problem.


THROTTLE POSITION SENSOR (TPS) - If a sticking throttle shaft or binding linkage
causes a high TPS voltage.
A "Scan" tool and/or voltmeter should read
less than 1.25 volts with throttle closed.


COOLANT TEMPERATURE SENSOR (CTS) - Using a "Scan" tool compare coolant temperature
with ambient temperature on a cold engine.
If coolant temperature reads 5 degrees
greater than or less than ambient air
temperature. Check for high resistance
in coolant sensor circuit or sensor itself.
Compare resistance value to the chart in
DIAGNOSTIC CHARTS/TROUBLE CODE CHARTS/CODE 15.


MANIFOLD ABSOLUTE PRESSURE (MAP) Sensor response and accuracy. Refer to
MAP voltage output check in DIAGNOSTIC
CHARTS/COMPONENT TESTING (C-CHARTS).


ECM/PCM grounds for being clean, tight, and in their proper location.
IAC operation - See DIAGNOSTIC CHARTS/ COMPONENT TESTING (C-CHARTS) and A-CHARTS.
P/N switch circuit. See DIAGNOSTIC CHARTS /COMPONENT TESTING (C-CHARTS), or use
"Scan" tool, and be sure tool indicates
vehicle is in drive with gear selector in
drive or overdrive.


NOTE: ^ Use "Scan" tool to determine if ECM is

receiving A/C request signal.
Whenever A/C is selected, refer to DIAGNOSTIC
CHARTS/COMPONENT TESTING (C-CHARTS).
If problem exists with A/C "ON," check A/C
system operation.



FUEL NOTE: ^ To determine if the condition is caused

by a rich or lean system, the vehicle should be
driven at the speed of the complaint.
Monitoring block learn will help identify problem.
LEAN: Block learn more than 150. Refer to
"Diagnostic Aids" in DIAGNOSTIC CHARTS/
TROUBLE CODE CHARTS/CODE 44.
RICH: Block learn less than 115. Refer to
"Diagnostic Aids" in DIAGNOSTIC CHARTS/
TROUBLE CODE CHARTS/CODE 45.


CHECK: ^ FUEL PRESSURE: use CHART A-7 in

DIAGNOSTIC CHARTS/A-CHARTS


FUEL INJECTOR BALANCE TEST (PORT-FUEL)
IGNITION CHECK: ^ SECONDARY AND PRIMARY SYSTEM.
^ IGNITION TIMING (NON-DIS).
^ For DIS/EST operation or misfire,

see COMPONENT TESTING (C-CHARTS). Check
ignition wires for shorts or faulty insulation.



EMISSIONS CHECK: ^ EVAPORATIVE SYSTEM use CHART C-3 in

DIAGNOSTIC CHARTS/COMPONENT TESTING/C-CHARTS.


EGR SYSTEM "ON," while idling, will cause roughness, stalling and hard starting.
PCV VALVE for proper operation by placing finger over inlet hole in valve end several times.
Valve should snap back. If not, replace valve.


AIR MANAGEMENT SYSTEM.
NOTE: ^ Refer to EMISSION CONTROLS

for complete testing procedures.



ENGINE CHECK: ^ VACUUM LEAKS can cause higher

than normal idle and low IAC counts.


BATTERY cables and ground straps should be clean and secure.
Erratic voltage will cause IAC to change its
position, resulting in poor idle quality.
IAC valve will not move, if system voltage
is below 9 or greater than 16 volts.


A/C refrigerant pressure too high, overcharge or faulty high pressure switch.
MOTOR MOUNTS.
CYLINDER COMPRESSION.




Some of that is just interesting reading, but it came from a forum post about a similar problem.

I will send a link to that site.  Go check it out.
You can read through without joining, but if you join, you can search, and ask/answer questions. Even joining is free, so that is the way to go.  A TON of good info on that site.
It is:

www.chevytalk.org/

I am in there in places as Fixitfox. May see you there.
Good luck,
Van