Author Topic: terrible idle at cold start up  (Read 10137 times)

Offline 1979C20

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terrible idle at cold start up
« on: December 06, 2010, 10:39:34 PM »
So winter rolled around and its finally getting cold. In the morning when I start up my truck, the right side of my exhaust dumps black smoke and the truck runs like its missfiring terribly. Its a 79 c20 with a 350 stock rochester qjet, headers, and true duals glasspacks. I have to rev up the engine to about 3k and hold it for like 15 seconds and it clears out and idles normal. What would cause this?
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline Irish_Alley

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Re: terrible idle at cold start up
« Reply #1 on: December 06, 2010, 11:59:56 PM »
a choke maybe. how cold is it and what do you have as far as emissions
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline 1979C20

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Re: terrible idle at cold start up
« Reply #2 on: December 07, 2010, 12:04:54 AM »
The choke works properly, after I get the engine to clear out, the choke keeps the idle at about 1100rpm and then when its warm, I crack the throttle and the idle drops back down to the normal 550rpm. All I have emissions wise now is the EGR. Removed emissions exhaust manifold, CAT converter, and AIR pump. Ive got headers and glasspacks now.
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline Irish_Alley

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Re: terrible idle at cold start up
« Reply #3 on: December 07, 2010, 12:14:32 AM »
i think not sure but i think a dirty egr can due that till it gets hot enough
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline 1979C20

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Re: terrible idle at cold start up
« Reply #4 on: December 07, 2010, 12:17:24 AM »
That sucks! Looks like its time to buy myself a EGR block off plate and just run no emissions. I forgot to mention, I pulled my vac canisters out too.
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline Irish_Alley

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Re: terrible idle at cold start up
« Reply #5 on: December 07, 2010, 12:49:15 AM »
Your idle is at 550? How you do that mine is at 900 it seams to run good there. I know if my choke is on at first its ok then it will load up and smoke and act like its missing till I give it gas to open the choke even with the choke on its only about 1100
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Irish_Alley

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Re: terrible idle at cold start up
« Reply #6 on: December 07, 2010, 12:55:13 AM »
just look at what other people said and 550 is about norm in park but even when I had my engine in my 86 with a th350 it would seam to only like to run 900 or higher in park so it wouldn’t stall in gear makes me wonder what I got in my engine lol
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline 1979C20

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Re: terrible idle at cold start up
« Reply #7 on: December 07, 2010, 12:57:02 AM »
Ive got a really large cam in it, so I can set the idle lower. Its got a nice grumbly rhythm to it. Runs fine. I ran it at about 7 or 8 for a while, but it seemed really high and I was burning a lot of fuel. But it runs smooth at 550. My truck is a manual also.
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline necromonger

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Re: terrible idle at cold start up
« Reply #8 on: December 07, 2010, 08:28:49 AM »
throw egr in trash.buy cover plate seal it good drive and be happy.
new build,1978 chevy 3/4 ton 2 wheel drive 350 4 speed trans.

Offline 1979C20

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Re: terrible idle at cold start up
« Reply #9 on: December 09, 2010, 11:13:22 AM »
where can I buy the cover plate, how much is it, and can I buy it locally or would it be from like summit or something? And, would unhooking the vacuum line from it work in the mean time?
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline Irish_Alley

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Re: terrible idle at cold start up
« Reply #10 on: December 09, 2010, 11:21:39 AM »
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline 1979C20

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Re: terrible idle at cold start up
« Reply #11 on: December 09, 2010, 11:37:14 AM »
What do you mean, irish?
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline screamin86

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Re: terrible idle at cold start up
« Reply #12 on: December 09, 2010, 12:01:56 PM »
I've always made the plates! I've got a couple of them I had on stock qjet manifolds laying around.I've got one on a cast intake and one on a aluminum factory intake.
86 k10 lwb 4x4:350 .040 214/224 444/466 112lsa performer rpm 1406 lt's summit racing th350 2800stall
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Offline 1979C20

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Re: terrible idle at cold start up
« Reply #13 on: December 09, 2010, 12:17:59 PM »
how do you make them? Pull the egr off, trace it on some sheet metal, cut it out and silicone it on?
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline Grim 82

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Re: terrible idle at cold start up
« Reply #14 on: December 09, 2010, 02:58:48 PM »
Pull the egr off, trace it on some sheet metal, cut it out and silicone it on?

Yes. Drill it before you cut it though.
Give a man a gun, and he might rob a bank. Give a man a bank, and he might rob the world.