1987 Chevrolet Custom Deluxe v20 rough idle

1987 CHEVROLET CUSTOM DELUXE
123,000 MILES • 5.7L • V8 • 4WD • AUTOMATIC
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EKRAFT94
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When I first start the truck it idles roughly and I have to pump the gas petal to get the truck to move. Once going the truck runs fine under acceleration but when the gas pedal is backed off to maintain current speed the truck runs rough or misses.
I have recently replaced fuel pump and filter and it ran fine for several days then this started. It also seems like it is worsening.
I have a service engine soon light on but am waiting for my code reader to arrive to check the code.
Aug 7, 2015 at 5:48 AM
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HMAC300
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to read code you onlneed a paper clip and cross A&B then with key on read check engine light flashes. If this is tbi unit check for a blown gasket under the tbi soft hoses sucking together going to map sensor on firewall. and any vacuum ose tha tis soft replace it.
Aug 7, 2015 at 5:56 AM
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EKRAFT94
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so far ive replaced the plugs, and wires. ive also rebuilt the throttle body and replaced the cap and rotor.
i tried checking timing but when i unpluged the wire to do so the timing didnt change.
Also ive noticed it runs fine when cold but verly pulls itself down the road when it starts acting up. if its under full throttle it runs great but when i back off the throttle to maintain speed it labors to stay running.
my next part to "throw at it" is the destributor but i also wonder if its not the electrical timing advance thats not working?
Thanks for your help
When i did get the check engine light to come on it went away as soon as i turned the key off to insert the paper clip to check code
all hoses ok and gasket under tbi is now new
Aug 11, 2015 at 2:36 PM
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HMAC300
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did you check vacuum hoses and other thing I said in first reply?like a vacuum leak? check compression as it may be a valve problem.
Aug 11, 2015 at 4:39 PM