Me and my buddy decided to take out his old sr that had a rod knocking problem and replace it with a new one but the problem is now is that when the car starts to run it sounds like its about to die. just wonder that his old motor was tweaked alittle that the ecu would have a problem with the new motor being stock.

 

no, the ecu wouldnt be messed up from rod knock, thats a purely mechanical problem
did u have to do nething with the ignition?
maybe a spark plug is bad or there gapped wrong, or a plug wire is bad, or maybe the dizzy cap/rotor,
what rpm does it idle at?
it should be at least 700rpm for idle, on some cars thats even low
it could be a various number of things
id go through and check ALL of you vaccum lines, if those are all good, then go through electrical components, namely the wiring harness- make sure everything is plugged in an where it needs to be, its very easy to over look a single plug or sumthin an it makes ur car run like a big steamy pile of **** and stuff
if thats all good then itll get a little more complicated, ull have to bust out the allmighty multimeter an start testing out ur wiring harness, looking for shorts, opens or bad grounds
if the ECU was fine before the engine swap and u swapped with the same engine then that shouldnt be the problem
u gotta go through an trouble shoot everything till u find the problem, especially with it being a new engine


hopefully its just an idle adjustment haha, neway hope i could help ya, good luck! let us no what u find!

 

even tho the old ecu was tuned it wouldnt mess up the new one?