Hey how’s it going - I have an 88bronco ii with the 2.9l & 4wd . Went to smog my car (California) n I passed everything but hydrocarbons (hc). My hc were fine at run speed but at idle the were between 300-700 . Mechanic said he noticed a misfire , although It doesn’t seem underpowered. Engine does seem to have a hiccup tho , you can see it shake every few seconds . He recommended just replacing the bigger catalytic converter instead of chasing this misfire around. While I will still replace them since they’re the 30year old stock ones I still wanna fix the misfire .

My engine runs between 850-900 rpm at idle

replaced spark plugs , rotor , intake and valve gaskets and all fluids with past 3 months.

Im thinking vacuum leak , or fuel issue

mabie a bad oring on fuel injector idk

im going to spray around for a vacuum leak, and use a thermometer to check for difference in cylinder temps . Anything else I should check /do ?

Wouldn’t advance timing cause a rough idle?

And I could see spark and cap , I’ll see what I can find out. Is there any way to check them?

I’ll check the timing just Incase but with the engine hiccups, my rpm never drops , stays between 850-900 almost always. Is there anyway to check wires and see what they’re output voltage is ?

Checked timing it’s fine as far as I can tell , I new to the timing portion of my car , used a stethoscope and injectors all match , however I did notice when I pulled my cats off the first cat has small pieces missing around the edges - could back pressure cause a misfire or slight hiccup? Seems slightly better after washing the cats out (haven’t gotten new one on yet , need to make a custom adapter for new cat) .