I have an 87 RS with a 2.8L V6/5spd. I changed the thermostat to 180 and fan switch to 200/185. The problem is that the idle is running high all the time. The TPS and IAC are new and adjusted properly. I can set the idle in the driveway, but it resets itself once driven above 35mph so I know its not a vacuum leak. I finally got access to a scanner to check all the sensors and it seems as if the system doesn't go closed loop until the temp is around 180-185. I thought it was supposed to go closed loop at 120. Does anyone know what temp it is supposed to run closed loop? I know these cars were designed to run hot, but running above 230 most of the time is not what I call pleasant.

 

145 my friend.

 

I was under the impression that closed loop happened closer to 100F and that the oxygen sensor was the major component that determined when it went closed loop.

 

I thought it was supposed to be a lot lower than what i am seeing. Yes, the book does say that the O2 sensor must be active to go closed loop, but doesn't say any temp range. just says coolent temp must be high enough what ever that is. Since I have not changed the o2 sensor since I've had the car and it may be the original with 170K miles on it, I am going to change it.

 

You'd have to check in the chip programming but my understanding is it's only gotta be about 100*F. The O2 cross-counts are the major factor in the ECM deciding that the Ox Sensor is up to temp and ready to deliver reliable readings. i.e. it's ready to go into closed loop.

 

My 92 5.7 goes into closed loop at 116F.

 

How do I find out what the chip programming is set to? Do I need a programmer to see this?

Thank you all for all the information. I now have another problem I have to deal with. #5 cylinder is fouled badly and the radiator emptied itself with no visable signs of leaks. I hope its not a cracked head.

 

Ya it don't change until the oxygen sensor is up to temp where it can give a proper signal. The two wire ones don't work or signal right till at op temp.
engine temp is realtive but not an accurate gauge.

Out side temp is a bigger factor. 40+ it only takes my V6 5-6 revs. As you know the car will rev up to around 2000 n back down on its own until the sensor is warm. Its pre warming its self so its faster, yet its sort of annoying having your car rev up n down like that. but in temps of 30f n below I won't let it idle on its own for long as it takes forever. Easier to just drive. As it does get annoying hearing your car rev up n down for several mins.

easiest fix is just get a $15-$20 3 wire O2 off Ebay. It was darn near invented to cure that problem. The extra wire isa hot wire to pre warm the O2 so it work right, right away.

I actualy got a 3 wire here somewhere but haven't got around to it.
Got it by mistake when I needed a 4 wire for our Subaru.

 

You should be careful not to confuse "Closed Loop Mode" and the tempreature at which target idle RPOM is "normal." There is a table of idle RPM versus coolant temperature. With stock programming, the "normal" target idle RPM occurs around 172ºF and above.

There are a lot of other temperature-dependent parameters besides just having the fuel trim in closed loop. The ECM will not update the BLM tables below 158º. The evap won't purge below 176º. And there are many others.

 

Closed will be entered when "all" of the following conditions have been met:

1. The oxygen sensor has varying voltage output, indicating it is hot enough to operate properly.
2. The coolant sensor is above a specified temperature.
3. A specific amount of time has elapsed since the engine was started. The specified values for conditions mentioned above vary from model to model, and are stored in the ECM PROM.

I believe that with OBDI the CTS had authority over the O2 sensor because of the time it takes for the O2 to warn up. With OBDII the heated O2 sensor now has authority over the CTS, or ECT. Whic makes sense because emissions is OBD's priority, example:
My 1999 OBDII S-10 would chug when shifting gears (auto) when cold, but OK when hot.
My Scanner showed my ECT intermittent below 140°F, but the PCM was in closed loop at 76°F. Changed ECT, no more chug.


I have found an ECM constant for Closed Loop Temp in some ECM parameter lists, but not in the $6E bin file that I'm using in my '88.
Would I change the Desired Idle Speed VS. Coolant Temp to go closed loop sooner if I change to a heated O2?

I haven't been able to scan data, so would anyone care to post scan data that showing at what CTS temp their 3rdgen ECMs go into Closed Loop?

For OBDI if you can't change parameter(s) to allow it to go into closed loop sooner, the only advantage to a heated O2 is lower emissions during open loop.

 

Read what Vader & rgarcia63 posted. They are both correct.

rgarcia63, the Closed Loop Enable Temp on a couple bins (AJUL & ARAP) for the 6E bins is 40.25*C (104.5*F). The Closed Loop Enable Temp is defined in TunerCat's 6E TDF. If you are using TunerCat, then your TDF is too old and you need a new one.

If you are using something else and want to define it, the constant is located at x'C445

 

Oh yea we can get detailed but I think he is just trying to stop that typical V6 cold start rev. Only wayto stop that is to get the O2 up to temp asap.

3 wire mod is the easiest fix. That or just don't let it idleon its own.

 

Until the CTS gets to the proper temp (which is what the original poster asked), it will never go into closed loop regardless of the O2 sensor temp.

 

Thank you everyone for your replies. My last post mentioned a fouled plug with coolent loss. Well, the head gasket went and dumped into #5 cylindar. I am now back running and with a new O2 sensor, the idle is back to normal and running closed loop as it should. Since it was already hot when I put the scanner on, I'm not sure at what temp it went closed loop, but it was steady with all parameters reading normal.

So I believe it was the O2 sensor that was causing the original problem. All is well for now and the car just left on a long trip as my son is heading back to college.

thanks,
jeff