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1990 GMC s-15 idles up and down
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crkresen
New User
Mar 30, 2014, 12:41 PM
Post #1 of 10
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1990 GMC s-15 idles up and down
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I have a 1990 GMC S-15 4.3 motor, When you start up the idle goes up and down to where sometimes it stalls out. have replaced tps, iss , and ecm. have checked for vacuum leaks. don't know what to look for next. any suggestions?
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kev2
Veteran
Mar 30, 2014, 1:22 PM
Post #2 of 10
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Re: 1990 GMC s-15 idles up and down
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check for codes, clean TB esp the bleed hole for the IAC- double ck for Vac leaks- use spray trick- be sure EGR is seating sometimes carbon binds pintel.
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crkresen
New User
Mar 30, 2014, 4:04 PM
Post #3 of 10
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Re: 1990 GMC s-15 idles up and down
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thank you for your reply. have cleaned throttle body, do i need to take out EGR valve and clean?
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 30, 2014, 10:50 PM
Post #4 of 10
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Re: 1990 GMC s-15 idles up and down
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EGR: Pintle as mentioned by DS could be not seating and to get a real clue take it out and look - carb cleaner thru it pushing pintle on block of wood or similar. Have a new gasket if removed as it will probably tear it up,
T
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crkresen
New User
Apr 7, 2014, 12:41 PM
Post #5 of 10
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Re: 1990 GMC s-15 idles up and down
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Thank you for your reply. took off egr valve and cleaned with carb. cleaner, still same idle pattern. any other suggestions?
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Apr 7, 2014, 2:32 PM
Post #6 of 10
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Re: 1990 GMC s-15 idles up and down
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How are you checking for vacuum leaks? Un-metered air is going to confuse the thing especially at idle which is why it was mentioned early here. PCV system and all hoses. Right up to vacuum hose to brake booster - all possible places of throttle body, housing to manifold, manifold to heads etc.,
T
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Discretesignals
Ultimate Carjunky
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Apr 7, 2014, 3:28 PM
Post #7 of 10
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Re: 1990 GMC s-15 idles up and down
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Also make sure your EGR valve isn't getting a vacuum signal at idle.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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car1104
User
Apr 13, 2014, 8:19 PM
Post #8 of 10
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Re: 1990 GMC s-15 idles up and down
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I had a 4.3 that idled up and down. Never stalled but does the problem clear out after running for a while? I suspected the alcohol --gas mix needed time to mix better. I changed gas stations for a while and stayed on premium gas, my problem when away.
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crkresen
New User
Apr 22, 2014, 8:47 AM
Post #9 of 10
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Re: 1990 GMC s-15 idles up and down
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how do you check to see if egr valve is getting vacuum signal
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Hammer Time
Ultimate Carjunky
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Apr 22, 2014, 8:51 AM
Post #10 of 10
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Re: 1990 GMC s-15 idles up and down
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Just pull the hose off when it's idling and you will feel the vacuum. You will also hear the engine clear up if there was vacuum.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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