i have been having problems with my idling on my truck. I will idle fast sometimes and idle so slow it dies sometimes. This evening it went out and when i left the house the truck was idling just fine. When i got to a red light about 15 minutes later it was idling so slow it was about to die. when i got where i was going about 2 minutes later, it was idling fine again. its manual choke and i have the fast idle cam disconnected so i know its not it. any ideas??

 

Hey,

What year truck? FI or carb? Power breaks? Any engine modifications? Let me know so I can take a shot at it.

 

[updated:LAST EDITED ON 23-Nov-02 AT 06:28 PM (EST)]its a 1970, no modifications. 1bbl carb. manual everything. 240. just been rebuilt(new gaskets, bearings, head job, lifters) Also, it has a hesitation in it.

 

Sounds like a vacuum leak. The intermittent behaviour makes me think you may have some crude in the carb or filter.

 

dont think its crud in the carb or filter because i checked that. what would be the best way to go about checking for a vaccumm leak. Also, ive asked this before and no no one knew, my truck has a little canister thing with a spring at the bottom if it that the vaccum hoses all come together at, kinda like a junction block. two of the lines go toward the carb and the other goes to the vaccum advance. it looks like it has an adjustment on the spring. do you have any idea what this is and how it could be adjusted???

 

If I'm reading this correct: you have a some sort of union box that has three hoses. Two go to ports off the carb, one goes to the vacuum advance on the dizzy. I'm not sure, but my guess is that the spring loaded union is some sort of thermostatic (temperature controlled) valve that switches between ported vacuum siganls off the carb to the dizzy. You could try testing it out by hooking up a vacuum gage to the outlet and seeing what (if any) difference there is between warm and cold PORTED vacuum (if this doesn't work pull the whole valve assembly and try pulling a vacuum on the two outlets that go to the carb, then try heating it up with a hair dryer (carefully) and trying again.) - What other vacuum lines are connected to the carb or manifold? I recommend going to an auto part store and buying some plugs to cap off any superflous vacuum connections. Get the truck good and warm and disconnect as much as possible. I assume all you have that's vacuum controlled would be the tranny (if you have AT), maybe a brake booster (if you've got power brakes), maybe a heated air intake door on the air cleaner (usually not vacuum controlled on your age truck)..anything else? Try to disconnect as much as possible - keep your brake booster and tranny connected (if you have them), but remove anything else (cap them off). Time the dizzy without any vacuum lines on the advance, check for what kind of vacuum difference there is between the two ports off the carb - reconnect the advance to the carb port that has no vac at idle & take it for a test drive. The intermittent part about the idle makes it seem like your getting too much advance some times and not enough at other times. I wish I knew more about the older vintages, you may want to try the appropriate year forum. Good Luck & keep us posted.

 

nothing on the truck is vaccum controled except the vaccum advance. everything else is capped off. Would maybe just running the lines straight to the dizzy and not go through the union help it??