: hard start, hi reving cadillac after storage

09-09-12, 08:58 PM
hello, i have been here along time, owned a couple Cadillac and i like to think i know my way around my engine, except for today.

2001 dts 185K miles

i put my car away for storage at the begin of the summer season, it would occasionally rev to 2500 ish but then idle down at a stop light, i just thought my iac was going and i would take care of it come fall when i pull it out ( now).
so now i am pulling it out of storage, well my problem is super bad now and no end in sight yet.

here is my delima.
my temp sensor doesn't appear to work any more!, pulled the sensor out and shorted it to ground to verified the wiring was OK ( needle went to 3 oclock)... great fine new sensor... well its in. but now it will register and then flip back to 9 oclock ( ice cold) every so often over bumps random time at idle etc etc... strange( yes i check the connector many times nothing loose )
next i borrowed a IAC off my perfectly working Eldorado to put it in my car, i installed it and immediately i noticed it was better. however now driving it for a while it would rev out to 3000 rpm slowly, WHEN it does idle it idles at 1200 rpm. ( all with a non working temp gauge)
I was driving and it would drive ok but once in N it would slowly climb to 3000 where it would stay, then id shut off the car and NO START, all my car would do was crank, crank and crank and crank with a huge smell of fuel. till i let it sit for 3-5 mins and i could get it started only if i flutter the gas peddle.
i realize my temp sensor not working doesn't help this out at all, and the reason it cranks probably because i shut it down at 3000 and the engine is likely flooded
so what i have now is a temperature sensor that doesn't register a car that wont start when hot, a iac motor that cant control where it idles and all with no codes.
there are no codes to speak of except P0118 ( tempo sensor circut hi)

so i start trouble shooting, i clean off both alternator grounds and the ground by the engine temp sensor, un hook the battery and re attach it make sure good connections there, unplug my sensors and re plug.
my temp sensor will not even get a signal. with it shorted to ground now it wont even go to 3 oclock,
and WHY is this thing reeving to 3000 rpm but when it does idle it idles at 1200 rpm.
car cold it seems to work fine
im baffled!
i think its all related to my engine temp and a bad wire... but where!!!!!
please help.

09-09-12, 09:36 PM
I'd start with a good TB cleaning.

09-10-12, 12:57 AM
:yeah: start with TB cleaning. Symptoms my Deville had with a super dirty gummed up throttle body.

09-11-12, 12:38 AM
Get your coolant temp sensor sorted first, then move on to the IAC.
This should help:

Engine Coolant Temperature Sensor
The Engine Coolant Temperature (ECT) sensor is a thermistor (temperature sensitive resistor) located in an engine coolant passage. The PCM supplies and monitors a 5-volt signal to ECT sensor through a resistor in PCM. This monitored 5-volt signal is then reduced by resistance of the engine coolant temperature. When coolant temperatures are low, ECT sensor resistance is high, and a high monitored voltage signal is seen by the PCM. When coolant temperatures are high, ECT sensor resistance is low, and a low monitored voltage is seen by the PCM. After engine start-up, temperature should rise steadily to about 194F (90C), then stabilize when thermostat opens.

Engine coolant temperature signal is used in the control of most systems the PCM controls (i.e., fuel delivery, ignition timing, idle speed, emission control devices). After a vehicle has been parked overnight, ECT and IAT sensor signals (resistance and temperature) should be close to same reading. An ECT sensor which is out of calibration will not set a diagnostic trouble code but will cause fuel delivery and driveability problems. Failure in ECT sensor circuit (open or short to ground) will cause monitored voltage to swing high or low and should set a related diagnostic trouble code.

Idle Air Control Valve
The Idle Air Control (IAC) valve controls engine idle speed during engine load changes to prevent stalling. The IAC valve is mounted on throttle body or on upper manifold assembly, and controls the amount of air by-passed around the throttle plate.
When engine is idling, PCM determines proper positioning of IAC valve based on battery voltage, engine coolant temperature, engine load and engine RPM. If engine RPM is too low, pintle is retracted and more air is by-passed around the throttle plate to increase engine RPM. If engine RPM is too high, pintle is extended and less air is by-passed around the throttle plate to decrease engine RPM.

If IAC valve is disconnected or connected with engine running, IAC loses its reference point and has to be reset. Resetting of IAC is accomplished on some models by turning ignition on and off. Problems in IAC circuit should set a related diagnostic trouble code.
The IAC valve affects only the idle system. If valve is stuck fully open, excessive airflow into the manifold creates a high idle speed. Valve stuck closed allows insufficient airflow, resulting in low idle speed. For calibration purposes, several different design IAC valves are used. Ensure proper design valve is used during replacement.