On a 92 LT1, using datamaster, why would my target idle RPM change while the car is running? Looking at the file, it changes 3 or 4 times in a matter of 5 minutes. It changes from 688 to 663 to 675 RPM. I thought this value was programmed into the chip as the idle speed and this is what idles speed the cengine trys to maintain. I know on my 96 Lt1, it was locked at 800 and never changed. Could this be a sign of a bad ECM or EPROM? It is a stock EPROM in there now with no tuning. It is also a remanufactured ECM. What is the target idle speed for a 6 speed car?

Thanks!

 

It will change only on startup.
When you start the car the coolant will be say... 25°C
the chip is programmed to be at 25°c at 700 Rpm
These are suppOsed value... not real...JUST FOR THE EXAPLE...
During the time the coolant progressively warms... the idle level programmed in the chip becomes lower.
When the car is fully warmed, the "Target idle" in the datamaster log should be stable.
-Beppe-

 

I figured that out after I posted this, but I am still not sure the target idle should be down around 650. I have read everywhere that a 6 speed should idle at 800 RPM.

 

I have datamaster too for my 90 L98.
And for sure what datamaster says as "target idle RPM" is what it read on the chip.
-Beppe-

 

That is a fairly low idle. Has the chip been reprogrammed? I believe it should never get any lower than 700 or 725.

 

The chip has never been programmed. It seemed kind of low to me too. I looked back on all the Datamaster logs I had and they all show 663 RPM when the car is warmed up. I looked at my last datalog and it showed 750 after it warmed up. I had unhooked the battery before the last datalog, but that shouldn't affect the target idle.

 

I don't understand...
you have 663 as target idle and then when the car is warm it idles at 750?
the 750 you are seeing is:
the reported actual RPM on datamaster?
the reported actual RPM16 on datamaster?
The reported target Idle rpm on datamaster?
the reported rpm sown on the tach?
With the car in Neutral you have different values from Target idle and reported RPM?
the IAC values?