Rough Idle - The 1947 - Present Chevrolet & GMC Truck Message Board Network

cdub · 08-24-2005, 08:19 PM

When I stop at a redlight, my truck's rpms go way down, and the oil light flickers, and it eventually...dies, if I don't give it a little gas. I believe there is a high lift cam in it, and I read that that may be the reason for the rough idle, but I don't think it should be dying at stoplights.

red86chevy · 08-24-2005, 10:20 PM

The lift of the cam would not cause a rough idle... duration and a low Lobe seperation angle will. If you do have a big cam, sounds like you may need more stall. Maybe it needs to run a little leaner? Does it chop at idle in park or only in drive?

you need to know what cam you have. It could be the cam, carb, or timing.

JMO,
Jeremy

*rage'nrat638* · 08-24-2005, 10:39 PM

vacuum leak.....

ureckme · 08-24-2005, 11:31 PM

Vacume leak or running to rich, can you smell unburned fuel, check vacume hoses, but I think a vacume leak would make it idol high. One thing I have seen is the bolts holding the carb down loosening up. With out enough info it could be any thing. Matt

Nolowrider · 08-25-2005, 07:47 AM

Is this something that just started? If it just staarted I would check all of your vacuum lines and check for a leak somewhere, like mentioned above. If it has always done this, since you had it anyway, I would hook a vacuum gage up to it and see what you have. A "high lift cam" will rob you of vacuum. How do your brakes feel? If the vacuum is good, I would look at the idle setting. I would start over by checking the timming first, then adjust the idle and eliminate that. Do you have the kickdown cable hooked up?

Slonaker · 08-25-2005, 10:35 AM

I had a rough idle on a car once that turned out to be a leak in the power brake booster. It was enough of a leak to cause a bad idle, but the brakes still worked pretty well. Weird.

Slonaker

cdub · 08-25-2005, 01:28 PM

It has always had a rough idle, it kinda sounds like a dragster. If you can imagine that. My father in law said he put a performance cam in it long ago. The carb is a 650 edelbrock, almost new. I do smell the fuel at redlights when it is ideling in drive. But...when it idles in neutral or park, it kinda smothes out, and doesn't sound like it wants to die. The brakes weren't working very well, I just had a brake booster put in the other day along with the headers and flowmasters. And now the brakes work well. I have tried everything to fix this problem. I believe it is too rich, how would I go about fixing that? I really have no idea how to set the fuel/air ratio on the carb, and I don't think it has ever been calibrated since I put it in. Anyone have any ideas? Thanks

Nolowrider · 08-25-2005, 02:24 PM

I would start here
It def sounds like you may be running rich. The reason I was asking about the brakes is because they use vacuum from the engine. When you are at idle and in park there is really no strain on the engine, thus should have good vacuum. When you drop it into drive, the vacuum will also drop and if you are already low not you are even lower. The power valve system works on vacuum. I would through a vacuum gage on it and see what you have. High lift cams will rob you of vacuum. Alot of people with big cams have to use a vacuum canister for the brakes to work good.

cdub · 08-25-2005, 09:22 PM

Well, I appreciate all the replys I have been getting, hopefully I will have time soon to work on it. hey nolowrider, that chart must have been written in like chinese or something, because I have no idea how to set the carb so she will run leaner. I know there are two knobs on the front of it, which is I believe the air and fuel mixture knobs. I dunno, if someone could break it down for me and really dummy proof it for me, that would be great, cuz I feel like a retard when I look at that chart. Thanks Chris

cdub · 08-28-2005, 10:30 PM

Well, after a quick inspection under the hood, I found what seemed to be the problem with my idle. The vaccum hose that connected right onto the vaccum advance was almost in two, not to mention the carberator bolts needed to be tightened as well. thank everyone for their advice, and knowledge. Chris

08-24-2005, 08:19 PM	#1
cdub Registered User Join Date: Aug 2005 Location: Fayetteville, NC Posts: 6	Rough Idle When I stop at a redlight, my truck's rpms go way down, and the oil light flickers, and it eventually...dies, if I don't give it a little gas. I believe there is a high lift cam in it, and I read that that may be the reason for the rough idle, but I don't think it should be dying at stoplights. __________________ 1976 K-10 1975 Silverado

08-24-2005, 10:20 PM	#2
red86chevy Registered User Join Date: Jun 2005 Location: sc Posts: 77	The lift of the cam would not cause a rough idle... duration and a low Lobe seperation angle will. If you do have a big cam, sounds like you may need more stall. Maybe it needs to run a little leaner? Does it chop at idle in park or only in drive? you need to know what cam you have. It could be the cam, carb, or timing. JMO, Jeremy __________________ 86 c-10 383 w/ sportsman II heads comp 286h cam Edlbrock RPM Performer intake Holley 750 th350 w/2400 stall 3.73 gears with powertrax No-Slip posi unit. Just broken in good. Will get a 1/4 time this week.

08-24-2005, 11:31 PM	#4
ureckme ureckmefixit2@cox.net Join Date: Dec 2004 Location: Mesa AZ. (Phoenix) Posts: 1,284	Vacume leak or running to rich, can you smell unburned fuel, check vacume hoses, but I think a vacume leak would make it idol high. One thing I have seen is the bolts holding the carb down loosening up. With out enough info it could be any thing. Matt __________________ That's U RECK ME FIX it 2 74 Chevy Short Bed 355ci Sportsman II 64cc Angle Plug Crower Custom Grind .462in .486ex Dyno Test 422hp @ 5600 And it's got a Holley 3.73 Gears 12 Bolt 3.73 w/Posi 700R4 Going In I'm a Body Man So There! That's why it's not painted

08-25-2005, 10:35 AM	#6
Slonaker Insert Witty Text Here Join Date: Oct 2002 Location: San Antonio, TX Posts: 3,415	I had a rough idle on a car once that turned out to be a leak in the power brake booster. It was enough of a leak to cause a bad idle, but the brakes still worked pretty well. Weird. Slonaker __________________ '86 Chevy C10 (Sold 04/19/13 ) Stock '01 Silverado

08-25-2005, 01:28 PM	#7
cdub Registered User Join Date: Aug 2005 Location: Fayetteville, NC Posts: 6	thanks It has always had a rough idle, it kinda sounds like a dragster. If you can imagine that. My father in law said he put a performance cam in it long ago. The carb is a 650 edelbrock, almost new. I do smell the fuel at redlights when it is ideling in drive. But...when it idles in neutral or park, it kinda smothes out, and doesn't sound like it wants to die. The brakes weren't working very well, I just had a brake booster put in the other day along with the headers and flowmasters. And now the brakes work well. I have tried everything to fix this problem. I believe it is too rich, how would I go about fixing that? I really have no idea how to set the fuel/air ratio on the carb, and I don't think it has ever been calibrated since I put it in. Anyone have any ideas? Thanks __________________ 1976 K-10 1975 Silverado

08-24-2005, 10:39 PM	#3
rage'nrat638 Account Suspended Join Date: Mar 2003 Location: THE FALL GUY CHICAGO IL Posts: 5,883	vacuum leak.....

08-25-2005, 07:47 AM	#5
Nolowrider Senior Member Join Date: Jan 2005 Location: New Orleans Posts: 1,365	Is this something that just started? If it just staarted I would check all of your vacuum lines and check for a leak somewhere, like mentioned above. If it has always done this, since you had it anyway, I would hook a vacuum gage up to it and see what you have. A "high lift cam" will rob you of vacuum. How do your brakes feel? If the vacuum is good, I would look at the idle setting. I would start over by checking the timming first, then adjust the idle and eliminate that. Do you have the kickdown cable hooked up?

08-25-2005, 02:24 PM	#8
Nolowrider Senior Member Join Date: Jan 2005 Location: New Orleans Posts: 1,365	I would start here It def sounds like you may be running rich. The reason I was asking about the brakes is because they use vacuum from the engine. When you are at idle and in park there is really no strain on the engine, thus should have good vacuum. When you drop it into drive, the vacuum will also drop and if you are already low not you are even lower. The power valve system works on vacuum. I would through a vacuum gage on it and see what you have. High lift cams will rob you of vacuum. Alot of people with big cams have to use a vacuum canister for the brakes to work good.

08-25-2005, 09:22 PM	#9
cdub Registered User Join Date: Aug 2005 Location: Fayetteville, NC Posts: 6	Well, I appreciate all the replys I have been getting, hopefully I will have time soon to work on it. hey nolowrider, that chart must have been written in like chinese or something, because I have no idea how to set the carb so she will run leaner. I know there are two knobs on the front of it, which is I believe the air and fuel mixture knobs. I dunno, if someone could break it down for me and really dummy proof it for me, that would be great, cuz I feel like a retard when I look at that chart. Thanks Chris __________________ 1976 K-10 1975 Silverado

08-28-2005, 10:30 PM	#10
cdub Registered User Join Date: Aug 2005 Location: Fayetteville, NC Posts: 6	Well, after a quick inspection under the hood, I found what seemed to be the problem with my idle. The vaccum hose that connected right onto the vaccum advance was almost in two, not to mention the carberator bolts needed to be tightened as well. thank everyone for their advice, and knowledge. Chris __________________ 1976 K-10 1975 Silverado



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