Hey guys/gals, I decided to register on this site because I've found a handful of helpful threads while doing some initial troubleshooting on my 720. For those who are curious, it's an '84 with the Z24 and automatic transmission. When I bought it, it ran fairly well, though it had a tendency to hesitate from a stop if you didn't feather the pedal. Regardless, it still got me home all right, so I was enthused. I did with this truck what I usually do with any vehicle I buy used. Do a little going over and tuning up/deferred maintenance. I'm not savvy regarding the correct lingo, so please be patient with me as I describe my issue. :)
When I bought it one of the thicker hoses coming from the air filter housing was plugged off by a screw and although there were a lot of OEM-looking rubber plugs on some of the carburetor hose barbs, there were still missing hoses that I couldn't identify the routing for and replace. It also looks like the two metal pipes that lead from some part on the exhaust to the air filter housing had been cut. It was also missing the pre-heater hose from the exhaust to the air filter housing. As I said when I drove it home, it was fine with the exception of needing the gas feathered when starting from a stop or it felt like it might die.
Anyway, I tried to use some carb cleaner and a toothbrush to clean the choke valve up top and I think it got misaligned or off track somehow, because that's when my high idle issues started (like 2k RPMs at idle). So I tried to fix the choke valve and must have corrected it somewhat because the idle went down to about 1200 RPMs. I then backed the throttle screw out a few turns or more, but it's still probably 800-900RPM. It seems like it won't go any lower no matter how far I continue to back that screw out. So as a result, even at idle, with the foot off the gas, I'm still cruising at 15-20 MPH. I'm suspecting a return spring might be stuck somewhere or possibly the throttle cable, since the gas pedal feels "soft" (doesn't have a lot of resistance).
Just last night I replaced the plugs, all wires, distributor cap and rotor (routed correctly and double checked) and buttoned everything back up just as I got it before, although I did replace the pre-heater hose. It was back to its previous high of about 2k RPMs and I'm absolutely puzzled. I tried turning the idle screw counterclockwise to absolutely zero effect - in fact, I backed it out so much it came out and I had to put it back in! At this time the screw that comes in contact with the dashpot has been backed off so that it is close but does not make contact. I'm not sure how to check the mechanism that controls the fast idle speed in park or neutral because the Haynes manual that came with the 720 is about as useful as a sack full of butt cheeks. I hate to be "that guy" who pops on right away with an issue, but I really need any help you can provide. I'm reaching the end of my rope. Thanks in advance, everyone!