Open/Closed Loop?

[IceWhite]

I would like to understand what is open loop and closed loop.
(What is it?, and how does it work?)
I have read it in a lot of threads and I think it has something to do
with o2 sensor and/or blue temp sensor, but not quite sure.
Could someone please explain.

Sorry for the noob question, but I am assuming this is what is
causing a problem in my car.

[mpowerful]

In open loop the computer is giving the motor preset commands to fuel based on how much you press the throttle. This set of parameters does not change.

In closed loop the o2 sensor feeds back to the controller and changes those parameters to adjust the air and fuel ratio of the output to stoichemetric efficiency, or afr of 14.X (usually around 14.5-14.7).

[digger]

the TPS and blue coolant temp sensor is an important part of the system as closed loop only happens after a certain coolant temperature is reached and the TPS WOT switch "turns off" the closed loop.

the purpose of closed loop is for catalytic converter efficiency and life

[IceWhite]

Thank you for the speedy responses guys.

So, for cars that do not have Catalytic converter and obviously no o2 sensor, does that mean open/closed loop do not exist
or
does it now mean that the Blue Temp Sensor [Quote "feeds back to the controller and changes those parameters to adjust the air and fuel ratio of the output to stoichemetric efficiency, or afr of 14.X (usually around 14.5-14.7)."].

[digger]

Thank you for the speedy responses guys.

So, for cars that do not have Catalytic converter and obviously no o2 sensor, does that mean open/closed loop do not exist
or
does it now mean that the Blue Temp Sensor [Quote "feeds back to the controller and changes those parameters to adjust the air and fuel ratio of the output to stoichemetric efficiency, or afr of 14.X (usually around 14.5-14.7)."].

no O2 = no closed loop

the bmw cars with no CAT have no O2 as there is no reason for it.

with regard to the closed loop system the blue temp sensor just relays the engine temp to the ECU so it knows that the engine has warmed up enough.

[IceWhite]

Thank You again for your informative and logical explanation.
Ok, so here is the real problem.
I have a constant high idle at anywhere between 1000 to 1100 rpm
Think its running rich and got poor gas mileage.

Before anybody says: Vacuun Leaks, it started out like this.

Brief History:
Car ran perfect, and the only non functioning item was the temp gauge on cluster,
which started out as SI Light problems, thereafter econo gauge stop functioning, dead rev counter, twitching/bouncing and
then dead temp gauge..
Replaced batteries and everything back to normal with the exception of temp gauge.
Started tracing and found that the fault was at the dreaded C191 connector. (Temp. Gauge was not getting signal from Brown
Temp. Sender. (Brown/Violet wire))
After unpluging it and cleaning it out and pluggin it together again, the car could not start. (We all know the C191 plug has the
temp sender/sensor wires and injection wires running through it.) Unplugged it and plugged it again car starts and temp gauge perfect.
Dead still at proper temp. Cluster function is Perfect.

Now the problem is this high idle. If the car stands for a while the idle will slowly drop to about +- 900rpm or even +-850rpm.
This car used to idle at +-750rpm.
Coming to a stop or traffic light is not long enough for it to drop a bit so it stays constant at 1000rpm
or sometimes 1100rpm.

I have noticed that when the car is idling high at around 1100 or 1000 rpm and I disconnect the electrical connector on the ICV,
nothing happens, but upon reconnection, the Idle drops to THE MAGICAL +-750rpm. and stays there. The sound of the engine is
quieter and engine seems relaxed. I can then drive the car and it would behave perfectly. It will always idle at +-750rpm, until I switch
the car off and when I restart it, I have to again unplug and replug the electrical connector on the ICV.

My questions are:
1a. Could by any chance my Blue Temp. Sensor now have the same problem as I was experiencing
with the Brown Temp. Sender (Temp Gauge on Cluster.) at the C191?
1b. Is the problem I am having now, is how the car would behave if the Blue Temp. Sensor was non functional. (High Idle)?

2. I don't want to mess again with the C191 plug, is there anything else that could cause this type of behaviour?

[dude8383]

Clean the ICV, check resistance at the blue temp sender AND check your TPS resistances as well.

[IceWhite]

^^ I agree and understand with what you say. I am going to check those that you mentioned above.

But... the real curve ball is when I unplug the electrical connector on the ICV and reconnect it again immediately the car drives normally.

[dude8383]

I had the same problem with my vert. Clean out the ICV and try again :up:

[ScottySbk]

hey quick question, im tracking down this rough idle/power loss at low speeds but once my cars warmed up it drives and idles great. Im quickly trying to understand what temp related could cause this and im now think my temp sensor is faulty ? i’ve unplugged my o2 sensor and it still runs rough. im trying to think about open and closed loops and try and understand what could cause this when cold.

[IceWhite]

Ooh Damn, Sorry for a very very late update to this thread. But, it was the cleaning of the ICV and making sure all attached hoses were properly clamped tight, is what solved the issue.