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92 chevy k1500 4.3 runs rough at idle rpm goes up and down…

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92 chevy k1500 4.3 runs...
92 chevy k1500 4.3 runs rough at idle rpm goes up and down sometimes dies no codes here is the weird thing is, when i hook up my scan tool and go into data display it runs fine when i exit data display it runs bad again
Submitted: 3 years ago.Category: Chevy
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Answered in 18 hours by:
6/25/2015
Chevy Mechanic: Lou P., ASE Certified Technician replied 2 years ago
Lou P.
Lou P., ASE Certified Technician
Category: Chevy
Satisfied Customers: 6,018
Experience: Building and driving Chevy's since I was in the womb!!!! Camaro and Corvette enthusiast, access to factory diagrams and tsb's
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ok, first , the ecm runs off the scan tool when the tool is hooked up so yes the idle will smooth out, so if there are no codes then you are going to have to go after common issues, throttle body leaks, fuel injectors dripping, idle air control valve sticking, throttle body base gasket, egr sticking, heres what happens, the engine starts , the ecm sees low idle or excessive air, so adds fuel, then the engine smooths out and the o2 sensors see to much fuel, so it lessons the fuel with gives lower rpms, and it keeps doing this trying to find the proper air fuel ratio, so the issue is with fuel or air. hope this helps,Please take a second and click the box and rate my service GOOD OR EXCELLENT SERVICE if you feel I have been helpful and please request me in the future. If you feel I have not been helpful please DO NOT RATE BAD OR POOR AND WASTE YOUR MONEY , I will opt out to see if another expert can provide more or better assistance so you're not wasting your money!!. Thanks for choosing just answer. Lou. also , if you feel i deserve one , BONUSES are GREATLY APPRECIATED ! 😉Keep in mind that rating me does not end the chat, it simply credits me for assisting, i will still be here to help if follow up information is needed , Lou.
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Customer reply replied 2 years ago
customer already throttle body, 02 sensor, map sensor, ecm, temp sensor, distributor and egr valve, can't get good data when it run right with scan tool hooked up. this one is kicking are butts!!!
Chevy Mechanic: Lou P., ASE Certified Technician replied 2 years ago
well the scan tool should do its own tests, there should be a option to test the system, i can t remember the exact verbalige. but how does the spray from the injectors look? nice mist? any drips?>
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Customer reply replied 2 years ago
NO DRIPS SPRAY LOOKS FINE RPM GOES UP AND DOWN UNTIL IT FINALLY DIES
Chevy Mechanic: Lou P., ASE Certified Technician replied 2 years ago
ok, how is the tune up how many miles on the truck?
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Customer reply replied 2 years ago
JUST TUNED UP NEW PLUGS, WIRES, CAP, ROTOR, AND DISTRIBUTOR COMP 160PSI ON ALL CYLS. 192000 MILES
Chevy Mechanic: Lou P., ASE Certified Technician replied 2 years ago
Ok try this. Take off the distributor cap, turn the engine by hand until you see the rotor move , then mark the crank to the engine. Now turn the engine back and see how far it moved before the rotor starts to turn. That will check the timing chain
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Customer reply replied 2 years ago
I WILL CHECK THAT BUT REMEMBER WITH SCAN TOOL HOOKED UP IT RUNS FINE
Chevy Mechanic: Lou P., ASE Certified Technician replied 2 years ago
I understand. With the scan tool like I said the car will Always run fine. I wish I had remembered why. I'll see if I can find out why. But I do know that the scanner controls the car at a baseline.
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Customer reply replied 2 years ago
NO PLAY IN CHAIN
Chevy Mechanic: Lou P., ASE Certified Technician replied 2 years ago
ok, i will opt out to see if another expert can help. sorry.
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Chevy Mechanic: Lou P., ASE Certified Technician replied 2 years ago
i have released your question so other experts can assist. hope it works out for you.
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Customer reply replied 2 years ago
THANK YOU
Chevy Mechanic: Lou P., ASE Certified Technician replied 2 years ago
no problem
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Customer reply replied 2 years ago
?????? any info yet?
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