recently, I found a small note about engine temperature sensors for Chrysler vehicles.
found it here
http://www.aa1car.com/library/coolant_sensors.htm
and it says:
When working on 1985 and up Chrysler products, watch out for a sudden voltage increase as the engine warms up. This is normal and is produced by a 1000 ohm resistor that switches into the coolant sensor circuit when the sensor's voltage drops to about 1.25 volts. This causes the voltage to jump back up to about 3.7 volts, where it again continues to drop until it reaches a fully warmed up value of about 2.0 volts.

does that apply for my engine (2,4 liter gasoline from '97)?
is that resistor a part of PCM or it can be foud elsewhere on the car body? where?
does anybody know what is the set temperature for resistor to switch in and out of the loop?

thanks

 

the resistor is in the sensor its called a NTC system

ENGINE COOLANT TEMPERATURE SENSOR - PCM INPUT
DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is used to sense engine coolant temperature. The sensor protrudes into an engine water jacket.

The ECT sensor is a two-wire Negative Thermal Coefficient (NTC) sensor. Meaning, as engine coolant temperature increases, resistance (voltage) in the sensor decreases. As temperature decreases, resistance (voltage) in the sensor increases.

OPERATION
At key-on, the Powertrain Control Module (PCM) sends out a regulated 5 volt signal to the ECT sensor. The PCM then monitors the signal as it passes through the ECT sensor to the sensor ground (sensor return)

When the engine is cold, the PCM will operate in Open Loop cycle. It will demand slightly richer air-fuel mixtures and higher idle speeds. This is done until normal operating temperatures are reached.

 

so, the resistor is inside the sensor?
great. thanks. I thought that might be the problem, but...

well, it's like this.
slightly tipping the accelerator when the car is stationary, rpm's are rising to about 2 000, then they hang at 2 000 for a few seconds, and then slowly, slowly droping down to idle.
even when driving, rpm's stay where they were after I remove my foot off the pedal. for example, I drive 4th gear at about 1700 rpm, I release the accelerator and press the clutch pedal. vehicle continues to roll, but the engine stays on 1700 rpm.

now, that wouldn't be the problem, but I checked most of the sensors, and they all look fine to me.
when the engine is hot, I read steady 2,56 Volts on temp. sensor (it also gives about 1,4 kOhms of resistance).
MAP sensor is changing the voltage in accordance with the throttle movement.
TPS sensor shows no sudden drops of resistance while the throttle is pulled.
IAC has been checked, replaced with good used one, cleaned.
O2 sensor is few months old, and is from Mopar.
there are no air leaks on intake manifold.

it is not the fuel problem, becouse the car runs on petrol and on LPG, and it shows the same problem on both fuels.

every once in a while, every few days, the car runs completly normal for a few minuites (usually when the engine is still not hot, but I can't provoke that at my will). it starts normaly (when it's bad, the rpm jumps to 2200 on start up, doesn' matter hot or cold) and revs drop imidiatly after I release the throttle. but then something happens, and it all goes bad again.

it does sound like the problem with MAP sensor, but I checked the voltage and it's OK. I checked it for a leak, but MAP is not leaking air.

anything else you can think of?
shouldn't there be a hole on the MAP for reference pressure?

I also tried to measure resistance on one of the temp sensor connectors (making sure the wires are not touching the ground). I connected one probe (digital voltmeter) to accu +, other to temp sensor connector. when I do that, I can hear 6 or 7 clicks from the intake manifold. when I disconnect, clicks can be heard again. and it can go all over again, every time I do that.
any idea what's making the clicks?
and it's not EVAP, it's not IAC. it's comming from intake manifold.

sorry for the long post, but I suspect you need a lot of information before any reasonable answer.

 

update

I got sick of that. can't normally drive, I was embarrased, people around me must thought that I cant drive, it sounded that bad.

quick solution, i disconnected MAP sensor.
check engine light came on, engine is just slightly lazier on start, but revs are dropping like a brick. smack down to 1 000 rpm when I release the throttle, and then slower to about 750.

problem solved untill I find new MAP sensor
tomorrow I'll just make sure it's not a bad conector or wiring.

new question (forget the previous ones)
-it seems that all 2,4 engines are the same. they are all slow on bringing engine revs down to idle.
is it possible to mount a MAP sensor from some newer engine? the one that would be faster?
which model?