Does anyone know at what point the pcm switches to "closed" loop, I don't have a problem changing parts but mine seems to do it mostly when warming up & before or just as the temp gauge starts to move. If it does not enter "closed" loop until the engine warms up & does not use the O2 sensor info until it is in closed loop then I do not think it would be the O2 sensor causing the problem, but I do not know at what point it switches from open loop to closed loop.

 

My truck does it whenever it wants. Sometimes after its warmed upsometimes when its cold, its all completely random. If the sensor is the problem what would the hissing/whining noise be coming from?

 

The link I posted has a very clear chart about when the engine is in open and closed loop. If I had any problem at all with the way my Magnum engine idled I would replace or at the very least clean the IAC valve and clean the TB like I stated above.If this hasn't been done on a truck from the 2nd gen ....it's very obvious by all the posts here that it should be.

 

I do not think I was clear & I am sorry for that. I was asking what decides when it switches from "idle "open" loop to "idle"closed" loop. Is it the coolant temp & if it is what temp decides this, if not does anyone know what decides this.

According to the chart provided (thank you very much for the link 982500Ram!) it says which sensors are used in which loop mode & most of them are self-explanatory, WOT etc. But when starting my truck & watching voltages & pressures I would like to know at what point it switches from open loop to closed loop at an idle because in open loop it does not use the O2 sensor input but in closed loop it does.

I am not trying to be difficult, I am a retired mechanic who no longer has his snap-on scanner or the information resources that I had a few years ago.

 

As far as I know it is coolant temp that determinesopen/closed at an idle. My truck took about 15 mins in the cool weather and the temp gauge would move about halfway to normal operating temp. The truck would then start to run very rough. My point in the post above was that I see many guys post here about idle problems and the "regulars" all tell them to clean the TB and IAC.

The first time I read this forum before I was even a member I got up removed the TB cleaned it in a bucket. It was filthy! Ibought a new IAC when I saw how black and crappy it looked. It just made sense to look at it after reading it so many times here.

 

Well I pulled the TB & cleaned everything out real well & had no change but while I had it off I also pulled the plug for the idle adjustment screw just as an after thought. So after letting it cool off again I started it up & brought the idle up about 75 rpm, it was idling cold at about 600 - 650 so it came up to about 725 & is no longer having this problem. Also with the slight increase in the TPS from adjusting the idle up the throttle response is better.

I did notice that the inside of the plenum has some oil in it so that would explain the P0308 cylinder #8 miss code that pops up once in a while so it will all be coming off again soon ;-(

Thanks a bunch for your help guys!

 

Adjusting the screw should not change the idle speed because the computer would adjust the IAC to get the idle back to 650rpm. Maybe the IAC is dirty or worn and not moving properly or sticking? Even though your truck is running better,I don't believe the idle screw was out of adjustment. It is possible there is still a problem.

 

Actually the throttle arm was dimpled in where it hits the throttle stop screw & the screw was flattened out as well. Judging by the wear on the gas pedal I think that after 160k of the PO sliding his foot off of the gas pedal instead of letting the pedal up so that it snapped the TB closed caused the damage. I only moved the screw .5-.75 of a turn, about .5 in actual movement & the TPS reading went from .64 up to .75 so that would explain some of the improved throttle response.

After 14 years being a mechanic & also doing smog checks in CA, the throttle screws on computer controlled TB's need adjustment more often than you may think ;-)

The #8 cylinder code was setting within 30-45 mins of normal driving after clearing the MIL & although I still need to do the plenum gasket The MIL light is no longer coming on. Eventhough the plug wires are new & routed perfectly to the TSB after changing the end on the dist end of the coil wire from a 90 degree boot to a straight boot so as to keep the coil wire away from the other wires, after a week of driving no more codes have been set for the #8 cyl or anything else.

 

That screw will adjust your iac counts. If you resolved any issues by adjusting it, then the iac valve might be your problem.

http://www.bionicdodge.com/Download/...a%20Magnum.pdf