Idle Woes

[jhstatts]

OK. Yesterday I did (almost) a complete tune-up: new fuel filter, new spark plugs, new wires, new distributor cap, new distributor rotor... and also did a chemical flush and refill of the radiator and a SeaFoam treatment through the carb. I need to change the PCV and change out the air filter, but I don't think my problems are coming from those two sources.

More background: recently put in new water pump, new fan clutch, all rad. hoses, all oil cooler hoses, new thermo.

Right after doing the work to the rad. and water pump, the truck started doing a little idle dance: when clutch was depressed, RPMs would drop down as normal, but then shoot back up to 1200 RPMs or so. I could get the RPMs down to normal by pulling up on the accel. pedal. Annoying, but workable.

So I thought a tune-up might be a good idea (and it was time). Yesterday and last evening, the truck ran pretty well, but was VERY sluggish on start-up... the choke didn't seem to do much either. I drove it around after it had warmed up and it drove very smoothly. The RPM dance was still there, but the pedal-thing worked again.

This morning I start the truck, Choke had no effect on start-up. Ran very rough and seemed like it wanted to die on me. Once warmed up, I start down the road... at the first light I stop, the RPMs then start shooting up and down, from 1200 to 1500 RPM in perfect "bursts" (vrooom, vrooom, vrooom). They kept doing it, so I drove back home.

Visible fuel in carb sight glass is normal.

Just started her up again and she idles high at 1500 RPM. Once warmed up the pulsing idle jump starts again (1200-1800 RPM).

Would the SeaFoam have caused this? What can I try to do? I am baffled.

Thanks for reading.

 

[jhstatts]

PS. I really need to get to work, so ANY help would be appreciated.

Thanks, all.

 

[jhstatts]

Wow... this is the first time one of my posts has gone more than 5 hours without an answer. You guys are slipping. Kidding, of course. I do need help, however.

 

[billmc]

OK I'll bite. Fluctuating idle like that makes me think vacuum leak. Did you knock a hose loose while you were doing all that? Seafoam won't hace caused those symptoms.

Bill

 

[Mr. Toad]

OK I'll bite. Fluctuating idle like that makes me think vacuum leak. Did you knock a hose loose while you were doing all that?

. . . or maybe hook up hoses in the wrong place. For instance, hooking the AC idle kick-up to the fast idle diaphram?

 

[jhstatts]

I don't think I crossed any lines or have anything loose. I checked them over yesterday. If it is a vac leak, it has to be a big one... and it kind of showed up overnight.

 

[bigbertha]

vacuum gauge my friend

Dude-

did you hook up a vac gauge yet? I feel your pain. Get a vacuum reading to rule out a leak, then go back and recheck your lines. also, you might re-check your timing. we just did that and it seemed to help a lot.

 

[jhstatts]

Dude-

did you hook up a vac gauge yet? I feel your pain. Get a vacuum reading to rule out a leak, then go back and recheck your lines. also, you might re-check your timing. we just did that and it seemed to help a lot.

Yeah, I read your saga. Well, here's an update... I went out and checked a few basics. Turns out my oil was pretty low. I put in a quart and a half, restarted and let her warm up. MUCH improvement in the sluggishness... and the choke seems to be operational again. I changed my oil about two and a half months ago (but I was thinking it had only been a month). Duh. Guess I will be more on top of the oil level from now on.

So, now I am back to the "idle dance." The one where pulling up on the pedal helps bring the idle back to normal. It is late now, but tomorrow I will check my idle mixture and idle speed screws. If that doesn't help, then it is on to tracking down a vac leak.

At least I can drive to work in the a.m.

Thanks for the posts thus far.

 

[Gordo]

Crazy!!!

I'm right there with you Man... I rebuilt my carb this weekend and have the exact same cyclic idle fluctuation problem. Mine also stumbles/stutters through 2k RPM.

My truck is desmogged BTW; it was prior to the carb rebuild and ran great (now wondering why I went and rebuild the carb…)

My carb has very few remaining vacuum ports that I still use, the rest are capped off. Due to this fact I doubt that my idle fluctuation is vacuum leak related. However, I am confident that it is carburetor related as opposed to ignition (though I guess it could be due to vacuum advance on mine).

Oddly enough I've noticed that the RPM fluctuation goes away when I unplug my fuel cut off/deceleration solenoid. If I unplug it without raising the idle speed prior, the engine will die.

When I raise the idle speed and then unplug, it idles without the cyclic fluctuation, but the RPMs end up rising and not coming back down as I drive it.

Will continue to troubleshoot mine and feedback what I find; let me know if you figure yours out and I’ll give it a shot as well.

Best of luck,
Gordo

 

[jhstatts]

Gordo,

I kind of figured mine out, but have to check on my idle mixture and idle speed tomorrow. I will report back at some point tomorrow night.

Good luck with yours. Idle issues suck.

 

[zmontgomery]

if you adjusted your idle at all, did you adjust the correct screw on the backside of the carb?? Or did you adjust the A/C idle up screw on the front, thinking it was the idle adjustment? I did exactly this when I first bought my cruiser, and it responded exactly as yours is doing......idle would jump from 1200 to 1500 almost all the time. Once I found where the real idle screw (and choke adjustment screw) were, I backed off the A/C screw and everything ran great. If it's not that, have you checked the vent hoses that come off the top of your distributor cap? one of mine fell off and the truck ran a little funky with it just hanging there. When I plugged it with my finger, the truck ran like s***......so maybe one of those hoses could be clogged?

 

[jhstatts]

z... thanks for the reply. I will check the A/C screw tomorrow as well. As it stands, I have not messed with the screws on the carb much at all.