Recently, my alternator died on me and I replaced it. I took it to this shop my mom had taken her Truck to get some work done on it. I would have gone to my normal shop but my ol girl had taken it upon herself to call this place and strike a deal They put the new one in, and I had to remind them to charge my dead optima battery before installing the new alt. Well everything was cool afterwards, the car has the best throttle response I've ever experienced in it. The only problem is, when I'm downshifting from 3rd into 2nd, if I keep my foot on the clutch too long, the RPM's drop to like 200 and the car threatens to stall (it shut off and turned right back on, by itself lastnight). It idles perfectly (900-950rpm), and that is the only problem I've come across since the new alt was put in. My cousin who's a mechanic says it can be my on board cpu, my clutch not engaging correctly or a problem with my battery connnections. Any idea what it could be?
Could be the clutch, but if it started acting up like that it would be one helluva coincidence. You might bleed it just in case. (Never hurts and probably been awhile anyways...)
I would think it could be your IAC perhaps taking a dump on you. Target idle is 750rpm. If you're idle is aroun 900-950, your butterfly in the TB could be misadjusted or your IAC could be hanging up. If the ECU is trying to use the IAC motor to adjust idle and it can't, things like this happen.
It used to be around 750rpm before I put the new alternator in. Now like I said its at 900-950rpm. But I did a few experiments. My RPMs only drop when I used my AC. Before the Alt problem they used to rise. But if I'm at lets say a light and rev the engine, the engine responds but instead of going back down to normal, it falls and almost shuts off... This on top of a minor vaccum somewhere, my idle isnt the best. And without my occasional AC things can get very unpleasent living in South Florida.
They put the new one in, and I had to remind them to charge my dead optima battery before installing the new alt. Well everything was cool afterwards, the car has the best throttle response I've ever experienced in it. The only problem is, when I'm downshifting from 3rd into 2nd, if I keep my foot on the clutch too long, the RPM's drop to like 200 and the car threatens to stall (it shut off and turned right back on, by itself lastnight). It idles perfectly (900-950rpm), and that is the only problem I've come across since the new alt was put in. My cousin who's a mechanic says it can be my on board cpu, my clutch not engaging correctly or a problem with my battery connnections. Any idea what it could be? 
