eliandzekespapa Posted March 28, 2013 Report Share Posted March 28, 2013 My truck is doing some crazy stuff...I cannot get it to Idle right. It idles high but when sitting still and running (idling high) I can hold the brake and slowly let out the clutch so that there is a load on the drivetrain and not enough to kill the engine, and the truck will idle lower without going back higher but as soon as I step on the throttle it returns to high idle . With all of the info about other peoples brakes and boosters I've been reading I seem to have alot of the same issues with mine. Could my booster be the cause of a vacum leak that is making the motor idle high? I've replaced all of the other vacum lines.I had intended to fix the rough idle before moving on to the brakes, but whatever gets it goin' you're right datzenmike...I should have started my own conversation... Quote Link to comment
metalmonkey47 Posted March 28, 2013 Report Share Posted March 28, 2013 Typically, you won't get a vacuum leak out of a booster unless your foot is on the brake, and the diaphragm is open (hence the leak.) Does it get worse when using the brake, even at idle? Is the truck new to you, and had this condition, or is this a new occurance after having it for a little while? Quote Link to comment
eliandzekespapa Posted March 28, 2013 Author Report Share Posted March 28, 2013 The truck is new to me by a few weeks so I'm still learning all of it's minor issues. Idling does get worse but not by much it actually falls lower in rpm when I step on the brake. I just got my haynes manual today so, that with you guys and my mechanic budy I should be able to figure it out...for now, I'm going to set the valve lash, disconnect all of the vacum lines and one by one reconnect them until something changes or all have been replaced and go from there. I have no front brakes and this could be just from a bad adjustment, air in the lines or a bad master, or a balloning soft line. I had planned on getting a simple tune going on the truck and moving on to the brake issue but as I read-- "vacum leak this and vacume leak that"-- in all that I read about the symptoms that I'm getting, I was just starting to think that my idle problems coud be related to the vacum on the booster. Quote Link to comment
datzenmike Posted March 29, 2013 Report Share Posted March 29, 2013 The biggest cause of bad brake performance on a '77 or older truck is not having the drum brakes adjusted properly. The further the shoes have to travel to make contact with the drum surface the further your peddle will travel. Lift the wheel and adjust the shoes in until they contact the drum. Spin the wheel by hand and when you feel the brake dragging you're there. Pump the brakes several times to center the sliding adjuster and check the drag again, adjust if necessary. Do all four. 1 Quote Link to comment
eliandzekespapa Posted March 30, 2013 Author Report Share Posted March 30, 2013 thank you ... I will do this tomorrow seems simple enough(brakes). Could anything electrical on the carb be causing a surge in idle? I hear a faint buzzing sound when I listen closely to the engine and the engine has, what seems like, a mind of its own when it comes to idling. It sounds like a sound little motor, no smoke, no ticking, no knocking...just won't idle RIGHT. Quote Link to comment
wayno Posted March 30, 2013 Report Share Posted March 30, 2013 thank you ... I will do this tomorrow seems simple enough(brakes). Could anything electrical on the carb be causing a surge in idle? I hear a faint buzzing sound when I listen closely to the engine and the engine has, what seems like, a mind of its own when it comes to idling. It sounds like a sound little motor, no smoke, no ticking, no knocking...just won't idle RIGHT. Check your PCV valve also, I had one go bad, and my idle went crazy. Quote Link to comment
datzenmike Posted March 30, 2013 Report Share Posted March 30, 2013 My truck is doing some crazy stuff...I cannot get it to Idle right. It idles high but when sitting still and running (idling high) I can hold the brake and slowly let out the clutch so that there is a load on the drivetrain and not enough to kill the engine, and the truck will idle lower without going back higher but as soon as I step on the throttle it returns to high idle . With all of the info about other peoples brakes and boosters I've been reading I seem to have alot of the same issues with mine. Could my booster be the cause of a vacum leak that is making the motor idle high? I've replaced all of the other vacum lines. If you want to eliminate the brake booster and it's hose, pull it off the intake and seal the hole. Still act the same way? Disconnect the vacuum advance hose to the dizzy. Still act the same way? Do you have an EGR valve still on it? Is the exhaust pipe still connected to it? Quote Link to comment
eliandzekespapa Posted April 1, 2013 Author Report Share Posted April 1, 2013 Please excuse the delay in response...I spent the day yesterday in BFN riding dirtbikes with my to kids... datzenmike : I have eliminated the booster as the culprit... using your technique. I do still have the egr control valve and yes it is still connected to the exhaust I'm going to take it off in a few minutes and check its operation and clean it why? What might it do to cause this issue? What should I look for? Quote Link to comment
datzenmike Posted April 1, 2013 Report Share Posted April 1, 2013 At idle it should be closed and off but they do get dirty and if so, may not close tight. If leaking it is reducing the amount of fuel and oxygen getting to the motor and the idle quality will suffer. Some 620s had a counter that turned an EGR light on on top of the dash every 30K, to remind to clean them Quote Link to comment
datsunaholic Posted April 1, 2013 Report Share Posted April 1, 2013 I had this symptom once. No matter what I tried, it wouldn't go away. I had to drag the idle down, or it'd climb all by itself. It would never return to idle on its own. What was happening was the carb's vacuum secondary was opening all by itself. Maybe the linkage was sticky, but I tried everything to make it go away, and the only solution was to replace the carb. Only that carb had that issue, and I put it in a different car just to verify, and it did the same thing. In the end, I went with a Weber and since Webers don't have vacuum secondaries the problem is gone. Quote Link to comment
datzenmike Posted April 1, 2013 Report Share Posted April 1, 2013 Could this be the BCDD set to a too low vacuum threshold? Too sensitive? Take the little rubber plug off the BCDD and turn the screw inside counter clockwise. This will raise the vacuum needed to turn the BCDD on and may then allow the engine to return to idle. This is the BCDD Quote Link to comment
eliandzekespapa Posted April 1, 2013 Author Report Share Posted April 1, 2013 once again datzenmike saves the day!!!! The BCDD wasn't allowing the truck's idle to fall. idle problem solved. thank you for the feedback and info. Quote Link to comment
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