My girlfriend just got this "used" blazer and I'm "trying" to fix it up for her but now I have this problem with the truck stalling at idle which it didn't do before until I replaced a bad O2 sensor. When she first got the truck it appeared to be running rich with stinking exhaust and black smoke coming out of the tail pipe when revving it. I did a tune up changing the cap, rotor, wires, plugs (old ones were covered with black soot) air filter. Got a code 44 with a "Service Engine Soon" light coming on so replaced the O2 sensor which was also black with soot andnoticed a new cat had been installed.After I replaced the O2 sensor the engine would sometimes idle rough after revving it a couple of times then stall at idle. I forgot to disconnect battery to clear all codes thinking maybe that was the problem for the stallingbut after clearing codes truck still stalling at idle.After the engine stallsit does not want to restart until I spray some starting fluid which then starts right up. The truck makes good power under full throttlebut I didn't check the fuel pressure as yet.I'mthinking maybea bad fuel pressure regulator or IAC but the truck didn'thave problem with stalling until after I replaced the O2 sensor WTF. Any help would be appreciated!!! Thanks

 

Update, I filled it up with BP Ultimate and added some fuel injection cleaner and took it on the highway for a half hour blast punching it a lot and now it idles OK with no stalling. This truck was sitting for a year with occasional 2 mile trips to the local stores so I guess it was pretty loaded up with carbon deposits and needed a good blow out. NEW PROBLEM now so if anyone can give me a pointer thanks.While on the highway I noticed the speedo is reading too fast for what I'm really doing. This blazer is a 4X4 with a 4 speed auto trans which looks like a 700R4. There's no speedo cable and I think I read it has a speed sensor instead. Any ideas on what is wrong? Thanks Again