Hey guys, I have a 91 S10 blazer, it has 127k on it, and ever since I've had it (about 3 years now) it has had a rough idle. On cold start up I can hear it misfire abit, after fully warmed up I would say it idles are maybe 600rpm? And it still has the rough idle while misfiring every few seconds.
I put a new timing chain on 2 years ago, upgraded to accel plug wires (stock wires were arcing everywhere) looked like a Christmas tree at night... Weirdest thing I've ever seen. Also replaced the coil. I reset and checked the timing after disconnecting under dash wire.
It got new plugs, cap and rotor about 2 years ago as well. Also usually has a little puff of Blue smoke on startup everyday, but otherwise doesn't burn oil.
I know one thing is that the exhaust stinks like crazy... Smells lean... Not rich or like oil at all. And every emissions test it passes with the Nox ppm at the exact limit every time. But I can literally smell the exhaust 100 feet away... Oh and recently my dash temp gauge stopped working. And I haven't replaced any sensors since I've had it.

 

have you checked and cleaned your IAC? does a 91 have a IAC? What engine do you have? as for the puff of blue smoke on startup could be valve seals, my Jimmy does the same thing, not ever start up however, but its the valve seals that causes it

 

I had that random light misfire at cold start too. I rebuilt my tbi throttle body and it eliminated that.

 

It's a 4.3, non vortec. It's getting pretty good mileage, I would say at least 18mpg, under load or cruising there's no misfiring or problems, though it seems like if I lug the engine around 45mph in over drive for a bit, then mash it, it really takes off, almost like it's loading up on fuel lugging it, and it has a ton of power. But other times is kinda sluggish? Maybe need a new fuel filter?
And I still have multiple lean misfires after its warmed up, which could account for the good gas mileage... Lol
I do believe it has also IAC I will check and clean it, though I have a memory of cleaning it a while back to no avail. Any other ideas?