Cold weather starting trouble. Need help. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

doodah man · 12-03-2011, 11:42 AM

This morning went out to start the truck in ~27* temps. It starts right away but the idle is really rough. I made a video on my phone and I'll post it in this thread if I can figure out the YouTubes.

So it idled rough and slow for about 5 minutes. I gave it gas every now and then, but it didn't feel like it was going to die. When the needle on the temperature gauge got to the first line, it smoothed out but was more like a fast idle; pretty high rpms. I blipped the throttle but the rpms would not slow down. I put it in drive. Still high rpms. Then I just drove it. It would get up to about 15 mph without even pressing the gas and I had to really get on the brake to stop it. Once I got it down the road a ways and it was fully warmed up, the idle was back down to normal, and I drove it 80 miles home.

The fast idle worked the way it's supposed to, until this summer. I noticed sometime this summer that it wouldn't drop out of fast idle when I blipped the throttle, but the rpm would usually drop when I put it in gear.

Is this the choke sticking or not working properly? It's a Rochester Qjet. Based on the casting numbers (7045213) it's a 1975 for a manual trans. I've got an automatic.

I sprayed it down on the inside with carb cleaner when I got home, but won't know if that did any good until tomorrow morning. Any ideas what might be going on? Thanks in advance as always.

doodah man · 12-03-2011, 09:48 PM

Anybody got any ideas?
Posted via Mobile Device

mrein3 · 12-03-2011, 10:51 PM

Is the choke the style that is operated by a bi-metalic strip under a tin heat shield? If so, after the truck warms but is stuck on high idle, carefully touch the raised area on the intake manifold under the choke thermostat.
If it is not hot, that passage may be clogged with carbon from the combustion process.
In a properly working, stock system, that passage heats up from exhaust gas and operates the choke through that bimetallic strip heating up. When that passage is blocked by 40 years of carbon build up the bimetallic strip won't heat up and work properly.
If this is the problem, the fix is to remove the intake and chip that crud out of there.
Posted via Mobile Device

Aaron Burkemper · 12-04-2011, 12:58 AM

You may also want to check the choke pull off. That may sometimes cause a rough initial cold idle until the choke opens a little bit.

12-03-2011, 11:42 AM	#1
doodah man Registered User Join Date: Apr 2011 Location: Philadelphia, PA Posts: 173	Cold weather starting trouble. Need help. This morning went out to start the truck in ~27* temps. It starts right away but the idle is really rough. I made a video on my phone and I'll post it in this thread if I can figure out the YouTubes. So it idled rough and slow for about 5 minutes. I gave it gas every now and then, but it didn't feel like it was going to die. When the needle on the temperature gauge got to the first line, it smoothed out but was more like a fast idle; pretty high rpms. I blipped the throttle but the rpms would not slow down. I put it in drive. Still high rpms. Then I just drove it. It would get up to about 15 mph without even pressing the gas and I had to really get on the brake to stop it. Once I got it down the road a ways and it was fully warmed up, the idle was back down to normal, and I drove it 80 miles home. The fast idle worked the way it's supposed to, until this summer. I noticed sometime this summer that it wouldn't drop out of fast idle when I blipped the throttle, but the rpm would usually drop when I put it in gear. Is this the choke sticking or not working properly? It's a Rochester Qjet. Based on the casting numbers (7045213) it's a 1975 for a manual trans. I've got an automatic. I sprayed it down on the inside with carb cleaner when I got home, but won't know if that did any good until tomorrow morning. Any ideas what might be going on? Thanks in advance as always. __________________ 1972 C-10 Deluxe 350 V8 - 350TH ------------------------------ We're not the jet set We're the old Chevrolet set

12-03-2011, 09:48 PM	#2
doodah man Registered User Join Date: Apr 2011 Location: Philadelphia, PA Posts: 173	Re: Cold weather starting trouble. Need help. Anybody got any ideas? Posted via Mobile Device __________________ 1972 C-10 Deluxe 350 V8 - 350TH ------------------------------ We're not the jet set We're the old Chevrolet set

12-03-2011, 10:51 PM	#3
mrein3 Registered User Join Date: Feb 2000 Location: Center City, MN, USA Posts: 3,254	Re: Cold weather starting trouble. Need help. Is the choke the style that is operated by a bi-metalic strip under a tin heat shield? If so, after the truck warms but is stuck on high idle, carefully touch the raised area on the intake manifold under the choke thermostat. If it is not hot, that passage may be clogged with carbon from the combustion process. In a properly working, stock system, that passage heats up from exhaust gas and operates the choke through that bimetallic strip heating up. When that passage is blocked by 40 years of carbon build up the bimetallic strip won't heat up and work properly. If this is the problem, the fix is to remove the intake and chip that crud out of there. Posted via Mobile Device __________________ '70 cab, '71 chassis, 383, TH350, NP205. '71 Malibu convertible '72 Malibu hard top Center City, MN

12-04-2011, 12:58 AM	#4
Aaron Burkemper Registered User Join Date: Sep 2011 Location: New Melle, MO Posts: 104	Re: Cold weather starting trouble. Need help. You may also want to check the choke pull off. That may sometimes cause a rough initial cold idle until the choke opens a little bit.



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