New Datsun 720 Owner With Fast Idle Cam Issue

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mphilleo
Posts: 1
Joined: Sun Oct 13, 2013 5:09 pm
Car: 1984 Datsun 720

New Datsun 720 Owner With Fast Idle Cam Issue

Postby mphilleo » Sun Oct 13, 2013 5:25 pm

Hey guys/gals, I decided to register here 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 (although it was warmed up), but 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 of 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.

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 1800-2k RPMs and I was absolutely puzzled. So I verified that as the truck warmed up and the choke opened, the fast idle cam moved out of the way as it would. After adjusting the idle screw and fuel/air mixture screw, the idle in drive and reverse was set to around the 650-700 RPM area that was advised by the EPA sticker under the hood. Even the idle in park and neutral is at a seemingly correct level. My issue is that when it's started cold again, the adjustor screw is holding on the part of the fast idle cam that what would be called the "third step" or largest section in the Haynes manual. When it's this high, the truck pulls pretty hard and will go to about 20-25 mph on its own in drive and rev pretty darn high again in park. I'm sure it's less obvious for guys who are driving a manual transmission truck but with this automatic, it's definitely revving high and I have to fight the speed with my brakes because I live in a 15 mph area. Is this normal and I should wait for it to warm up before driving? Or is there anything else I can do? If I have to rebuild the carb, I suppose that's what I'll have to do. ;)

Of course, it might be related to vacuum hosing being missing from these items, though I'm not sure where they go. 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!

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PEZi
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Re: New Datsun 720 Owner With Fast Idle Cam Issue

Postby PEZi » Thu Nov 14, 2013 11:45 pm

All sounds lead to a vac problem. Everything on that intake manifold, first off, needs a cap. If there is a vac line that used to run to something, the hole needs to be capped off. That should help on its own, but if not, just check and make sure there are no other vac leaks anywhere on the intake. If that doesn't fix it, report back and we can go from there! Hope that helps.

kbk67
Posts: 2
Joined: Thu Mar 26, 2020 10:16 am
Car: 1983 Nissan 720 long bed 4X4 2.4

Re: New Datsun 720 Owner With Fast Idle Cam Issue

Postby kbk67 » Fri Jun 19, 2020 11:50 am

I have been dealing with a idle problem on my 83 720 2.4 for a couple of months now and can tell you that it is like chasing a ghost around! One thing that I would do first is check the choke relay under the dash on the right (passenger) side wall. Put your hand on the relay and turn on the ignition switch and see if you can feel a click. If not then replace it.


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