Ok so I have just finished replacing the heater core (for the second time in a year) put the truck all back together and refilled it with Distilled water and motor craft brand antifreeze..... blah blah blah ..... anyway it will Idle just fine but in drive;It has a "miss" from about 1300 to 2000 rpm range... the last time I did this repair I plugged it in and got a lean on bank 1 code and a misfire on #7 code I swapped out #7 and another coil to see if the misfire would move and it did NOT. NO CEL or any other warnig lights were on last time or this time....Friend of my Dad Who works at a local chevy dealer says if the battery has been disconnected for any "length of time" The computer will have to "relearn" the engine..... I assume this may be correct because after a few hundred miles,the anoying problem went away.... So is there some truth to this "relearning"process or is there some "reset" proceedure I can perform? any help would be appreciated ..... thank you

 

Relearning.......yes.
Here is why.
All modern vehichles that run on computer also run on a base program.
In the program are many 'tables of data' the program references for controlling 'dynamic' operation over temperature ranges, rpm ranges, throttle openings, controlling shift points etc.
As the vehichle is used, these tables get added to and subtracted from over time.
It's these changes that get lost leaving the base tables left to run the motor after a power down event has been done 'called a reboot'.
When the motor is started and run on the base tables, it may be precieved that the motor will act differently until the tables are altered again per the driving the motor has been put to, over some time.
.
If there is a specific fault such as a cylinder missfire or a program initiated test has failed, this does not wait for a table to be rebuilt because it's not a rebuildable table that runs the engine but a maintaince table that never changes.
Good luck.

 

thnks Bluegrass..... for the info and response.....
I dont think if the dealer does this job that they would let the vehicle out with it running rough like that but I am Not a dealer ... I refuse to pay the rediculous amount of money they want for this repair.Also I doubt that they would go to the extent that I have with draining the block and using Distilled water to refill it and so on. I wonder if there is some "well kept" secret procedure they use to get it running right again when the customer picks it up and drives away ..... maybe not.... I just find it to be frustrating and annoying to drive it like this..... Last time I did this I went through the same thing with the poor performance for a few hundred miles and it just straightened itself out eventually.... grrrrrrr .... also the computer is Not giving any codes when I plug it in this time .... So I guess I will just give it a little time to do it's thing.
Thanks again for the info Bluegrass

 

You may have some preventative maintenance to do - you have some issues that only show up before it adapts. I'd be looking at spark plugs and cops (assuming V-8) to start with.

 

After my recent spark plug issue, i discovered part of my problem to be coolant leaking on a plug. This issue that i had was much like yours but went away in a much shorter time. This led me to believe the coolant had evaporated off, eliminating the problem. (this may be an incorrect assumption, but i am not sure) Since you just relplaced your heater core, what are the chances you may have gotten coolant on one or more of your plugs? Just something else to think about as you deal with this problem

 

I have been wondering about that posibilty of the coolant and or water getting into the plug wells during the flush or the hose replacement part of changing out the core,but I am not getting any misfire codes or any other codes for that matter..... The 2 times I have plugged it in I get a message about "IM tests Incomplete" so I dont know what to do after this point besides check for fluid in the plug wells .....
thanks for your input on this one guys....

 

So um uh er um yeah I am a drooling #!@*+@ vegetable sometimes.... And yeah I got A LOT of coolant in the plug wells .... Checked 1 through 4... a couple had quite a bit of "wet paste-like crud" in them. So I blew them out with an air nozzle,sprayed the hole with brake cleaner,blew it out again,reapplied the grease to the boots and had to change one coil. Put it all back together and everything is fine now.....