so all my vacuum lines are < 3 months old.. and since i was doing other work on stuff tonight i happened to come across this.. i've known for a while that my inside temp vacuum line was not hooked up.. and i've messed with the nipple for it on the intake manifold before with no change in engine operation.. my idle is a little rough but has been around the 700 range with a slight fluctuation lately but nothing that really has concerned me.. tonight I put my finger over the nipple and the engine dropped RPM to a point where it was starting to stumble a bit but was still running.. thats usually a vacuum leak characteristic.. but i'm plugging the only leak I know of and it does that.. I've recently installed 19lb mustang injectors and new FPR with no other mods to allow for more air for the additional fuel the mustang injectors provide in our system (~21.5 or so lb/hr I believe)..
could the problem I'm seeing be that the "leak" caused by my not having that line hooked up is giving the engine the extra air needed and thats why it seems to be running fine? and by me plugging the hole with my finger is making the engine run too rich and stumble? if so would my best solution be to fix the vacuum line and then tighten the spring on the AFM a couple knotches so that more air is coming in with the signal to the ECU about the air flow staying the same?
If that made sense to anyone feel free to give me your input on my situation
IMO, it's never a good idea to "tune" an engine by allowing vacuum leaks. Yes, you should plug it and adjust the AFM as per Icehaus' instructions (which are available in the archives of the old site). Don't forget to check the intake boot and the vent tube that goes from the valve cover to the intake boot.
i wasnt "tuning" it that way.. thats why i'm asking my question.. i just didnt know if it couldve been something else that was making it drop in RPM when i plugged that hole..
