new question, but a strange one! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jorgensensc · 11-20-2004, 11:15 PM

O.K. heres a strange one for you. When the truck is in park and idling at around 1200RPM, if I put my foot on the brake it idles up to around 1500 to 1600RPM. If I take my foot off the brake it idles back down. Any ideas??

nu2-72 · 11-20-2004, 11:19 PM

Power brakes? Vacuum leak somewhere?

Anything under the dash making contact with the acc. pedal?

cableguy0 · 11-20-2004, 11:21 PM

if its got power brakes the booster is probably leaking plug the line to the booster and see if that fixes it. 1200 is damn high for an idle though normal idle is around 700rpm

jorgensensc · 11-21-2004, 01:06 AM

It has power brakes. I will check that tomorrow. I know the idle seems high, but I was trying to adjust it based on the sticker in the engine bay. It actually says to adjust it to 1500 RPM in Park, and 600 in drive. IF I adjust the idle down to 800 in park I get like 350rpm in drive. For some reason I can't adjust the park idle and the drive idle seperately on the edelbrock 1406 I have. At least I haven't figured it out yet. When I adjust the idle screw it adjusts both park and drive idle. When I adjust the mixture screws I get the same results. Any suggestions?

cableguy0 · 11-21-2004, 01:18 AM

sounds like you have a major vaccum leak. it should be no higher than 800 in park drop to about 650 in drive or so

cableguy0 · 11-21-2004, 01:26 AM

there is no seperate adjustment for park idle and in gear idle it should never drop 500 rpm between the two. maybe 200rpm tops nothing more. the 1200 on the stick sounds like the high idle when the choke is engaged

66nova383 · 11-21-2004, 12:36 PM

My truck does the same,it idles at 700 in park apply the brake and it idles up to 800 pull it into gear and it idles at 600. I have a 670 holley and can't find any vacume leaks at all. And the brakes are real sensitive.

11-20-2004, 11:15 PM	#1
jorgensensc Registered User Join Date: Jul 2003 Location: Cypress, Tx Posts: 4,005	new question, but a strange one! O.K. heres a strange one for you. When the truck is in park and idling at around 1200RPM, if I put my foot on the brake it idles up to around 1500 to 1600RPM. If I take my foot off the brake it idles back down. Any ideas?? __________________ 1972 C20 Suburban- Big Blue Betty '56 Chevy Bel Air Sedan- Frame up Restoration -What would you attempt to achieve if you knew you could not fail?- -I Refuse To Tiptoe Through Life, Only To Arrive Safely At Death's Door- R.I.P. EAST SIDE LOW LIFE

11-20-2004, 11:19 PM	#2
nu2-72 Senior Member Join Date: Apr 2001 Location: Amazonia, Mo. USA Posts: 2,821	Power brakes? Vacuum leak somewhere? Anything under the dash making contact with the acc. pedal? __________________ 72 3/4 4x4 350 4spd 72 3/4 4x4 350 auto 2004 Duramax Silverado 4x4 2006 Duramax Crew cab 4x4 2010 Harley Ultra Limited 2011 Harley Street Glide

11-20-2004, 11:21 PM	#3
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	if its got power brakes the booster is probably leaking plug the line to the booster and see if that fixes it. 1200 is damn high for an idle though normal idle is around 700rpm __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

11-21-2004, 01:06 AM	#4
jorgensensc Registered User Join Date: Jul 2003 Location: Cypress, Tx Posts: 4,005	It has power brakes. I will check that tomorrow. I know the idle seems high, but I was trying to adjust it based on the sticker in the engine bay. It actually says to adjust it to 1500 RPM in Park, and 600 in drive. IF I adjust the idle down to 800 in park I get like 350rpm in drive. For some reason I can't adjust the park idle and the drive idle seperately on the edelbrock 1406 I have. At least I haven't figured it out yet. When I adjust the idle screw it adjusts both park and drive idle. When I adjust the mixture screws I get the same results. Any suggestions? __________________ 1972 C20 Suburban- Big Blue Betty '56 Chevy Bel Air Sedan- Frame up Restoration -What would you attempt to achieve if you knew you could not fail?- -I Refuse To Tiptoe Through Life, Only To Arrive Safely At Death's Door- R.I.P. EAST SIDE LOW LIFE

11-21-2004, 01:18 AM	#5
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	sounds like you have a major vaccum leak. it should be no higher than 800 in park drop to about 650 in drive or so __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

11-21-2004, 01:26 AM	#6
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	there is no seperate adjustment for park idle and in gear idle it should never drop 500 rpm between the two. maybe 200rpm tops nothing more. the 1200 on the stick sounds like the high idle when the choke is engaged __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

11-21-2004, 12:36 PM	#7
66nova383 Registered User Join Date: Jan 2004 Location: Albany Or Posts: 51	My truck does the same,it idles at 700 in park apply the brake and it idles up to 800 pull it into gear and it idles at 600. I have a 670 holley and can't find any vacume leaks at all. And the brakes are real sensitive.



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