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Hesitation and sputtering


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77gmc454's Avatar
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May 4th, 2012, 10:45 AM   #1  
Hesitation and sputtering

I have a 90 Chevy 1500 with a fuel injected 350 that hesitates when accelerating from a stop. Replaced fuel pump, coolant sensor, oxygen sensor, throttle positioning sensor, I even had an extra set of injectors I tried and nothing works. Runs ok after it gets going but is about to drive me crazy. Any suggestions and could it be the computer-no codes??

 
Allan In NE's Avatar
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May 4th, 2012, 10:59 AM   #2  
Fuel filter? Possible IAC motor.

Allan

 
77gmc454's Avatar
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May 4th, 2012, 11:01 AM   #3  
Done the filter. What is IAC.

 
Allan In NE's Avatar
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May 5th, 2012, 6:57 AM   #4  
Idle Air Control step motor; screws into the right side of the throttle body. Big fat thing, takes an 1" wrench to loosen if I remembr right.

A 'bog' or hesitation is caused by the mixture being way too lean.

The IAC's function is to set the mixture when the engine is cold and before it goes into closed loop. However, if this thing is 'mechanically' stuck in the open position, it would act must like a vacuum leak in closed loop.

Not saying this is your issue, just trying to help you eleminate another possibility. Does the engine idle too fast? Higher than about 600 rpm ?

Allan

 
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May 5th, 2012, 9:41 AM   #5  
I will give it a try. Thanks for your help.

 
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May 7th, 2012, 9:48 AM   #6  
Allan- You are the man! Had an extra injector housing and swapped controls and runs great again. Can't thank you enough, talked to many people and that was the first time I was told about the IAC. Thanks again.

 
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May 7th, 2012, 5:10 PM   #7  
could this be the same problem on a 97 k1500 350? i have only i bought the truck about 5k miles ago, and the only fuel part i have changed is the filter.
i only have the hesitation on my first takeoff after the truck starts

 
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