Quick run through on what I'm experiencing... Hoping for some advice on this:
I've always had some lag when switching HVAC controls from dash vents to defrost and what-not, i know this is normally a vacuum pump issue or blendoor. Never thought twice about, never really cared. Window is normally down in the summer anyways and it basically stays on Defrost in the winter. No problems there.
The truck has 240K miles on it now and still has factory original injectors. (Verified with last 2 owners
Got into a pretty serious accident a some time ago and got it repainted and the whole shibang. When I got it back, come to find out, when they painted all the new fenders, fender supports, and coated the frame, they attached all the grounds to the new painted surfaces which didn't help my already corroded, old, weak battery cables and grounds. This made the truck have a hard time stay running, starting, and when it would run, it would run really rough and through all kinds of codes. A few weeks of diagnosing and help from you guys, I replaced all of the battery cables and grounds from Custombatterycables.com and it seems to have solved all my problems.
Now on to the problem - After I replaced all the cables and paid more attention to my RPM making sure it wasn't surging like it was when I was having electrical issues I noticed that it had this really really slight surge at idle both hot and cold idle. Voltage stays at 14V the whole time (unless the grid heater is cycling). It's just enough for me to notice even outside the truck.
According to my Edge Insight - It drops ~50 - 100 RPM every minute or so. Then, just to throw me off, it will spike ~50 - 100RPM. Which leads me to believe it's a slight misfire caused by a failing injector. They're old... So I wouldn't be surprised.
Here's the kicker: It only does it when I have the blower motor on. Doesn't matter where it's blowing, hot or cold, A/C on or off. But if I turn the fan completely off. It doesn't do it at all.
The truck runs great though. To be completely honest, it could have been this way for as long as I've owned it and only noticed it because I was paying super close attention to it, looking for any kind of symptom after replacing the battery cables and grounds.
No Blow-by, no voltage drops, no smoke. The only other thing I can possibly think of that would lead me to injectors is that my fuel mileage has dropped by about 1MPG in the last few months. Since I'm in Utah and we switched to winter diesel before I got the truck back and most fuel stations still haven't switched back to "Summer Diesel", I feel that will account for the decrease.
I am known to over think things and be a worry-wart when it comes to this truck so there's that...