I started out this morning to try and troubleshoot the high NOx on my 92 740 B230F, Regina. I had already put on a new cat. Otherwise it has been running great. I figured there were 2 things to do - check timing and the O2 sensor. Today was the timing and I resolved to swap the belt while at it. I spent a good hour removing the small retaining bolt whose head the PO had rounded off. This involved use of a MIG welder. However, the timing was good and the belt looked good and I decided to leave the swap for another day. I merely reset the tensioner. The only other actions were to clean the engine ground at the firewall and wire up one new and one old horn.
Both horns hardly worked at all. I started the motor and it now has a 1300-1400 idle, vs 750 previously. It almost stalls when I engage D or R, and drives a bit nervously.
The other thing that is going on is that my 2-3 year old battery has now twice run down gradually over several days and needed a recharge to start. Charging voltage is 14.0

There is also an exhaust manifold leak, rear cyl I think.
HELP!