I've been having a few issues with my 1993 civic SI, and up until recently I've had nothing to really point me in the right direction. The check engine light came on today for a vague code of 43, which is just something with the fuel system as far as I can tell. I have already replaced the fuel filter, pressure regulator, and o2 sensor. The injectors were taken off and cleaned, they all sound fine when I put a screwdriver up to them and the resistance is consistent across all of them. When I checked the fuel pressure a while back prior to the engine light coming on, it seemed fine but my symptoms were the same so its likely that something else is at play here as well as whatever is causing the CEL to come on.

A few other things I have done include replacing the TPS sensor, PCV system, vacuum lines, valve adjustment, and new distributor cap, rotor, spark plugs, and wires. Something else I have noticed is that when I go to set the idle, it doesnt drop at all when the IACV is disconnected, and when I set the screw as low as it can go it will only go down to 1000 rpm or so. Sometimes, when im shifting the rpms can also either drop really quickly or extremely slow, taking up to 15 seconds to go from 3000 to 1500 (or wherever im trying to rev match really). Other times, it runs almost perfect and none of this happens. Its quite confusing to me and I am pretty inexperienced with diagnosis in general, and having a vehicle like this where I can't just plug in an obd scanner and get things like the fuel trims makes this significantly more difficult for me to figure out. Any help would be appreciated.

 

Based on what you’ve done, it sounds likely an IACV issue to me.

 

Its definitely possible, it looks like it was replaced in 2013 with an off brand one and I dont know the quality of it. But would the IACV affect acceleration or anything? Thats the part im unsure about. It could be something else completely or both.

 

If the IACV is not functioning, acceleration will be affected up to about 2500 RPM... causing sputtering and bucking.