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Hello I am having a strange problem with my 1999 Chevy Silverado 1500 4.3 base model.

I have replaced the PCV valve cap rotor plugs and wires and have cleaned the mass airflow sensor tested the AIT sensor, TPS and cleaned the EGR.

The problem I am having is either after a rain or on a humid morning the truck idles fine and starts fine but at light throttle it misses and throws no code after a the truck is fully warm and has sat at my first job it is fine for the rest of the day. The truck always feels like it is being held back a little and the missing is worst at maintaining speed throttle.

Any help would be greatly appreciated I have been fighting with this for a while.

Gunnar

PS I have also sprayed carb cleaner all over to check for either a vacuum leak or a bad intake manifold gasket but no change in idle.

Thanks again

Sorry to ask when I am so new here
 

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Welcome to the club Gunnar. Since this only does it when it's raining or humid out, I think it might be getting moisture on your plug wires & causing the miss. Next time it's humid & dark out, pop your hood & start it up & look for a light blue glowing or arcing around your plug wires & dist cap.
 

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Welcome to the club Gunnar. Since this only does it when it's raining or humid out, I think it might be getting moisture on your plug wires & causing the miss. Next time it's humid & dark out, pop your hood & start it up & look for a light blue glowing or arcing around your plug wires & dist cap.
Thank you for the reply Stephan I did that 2 nights ago and it was arcing, today I replaced the plugs and wires with OEM and the problem is still there (those plugs and wires were pricey from Chevy) Any other ideas?

Thanks

Gunnar
 

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The new ones shouldn't be arcing unless you got a little oil on them. Try cleaning them off with some alcohol & recheck them to see if they're still arcing. Also if they're arcing at the either end, then make sure your boots & caps are clean & the elect portion of the connectors are pushed in & on all the way. Same with the boots & caps. Anywhere you see an arc, there's a problem.

* Smth else, pull your dist cap & look inside. If the moisture & humidity is affecting your wires like this it could be getting inside the cap too.
 

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The new ones shouldn't be arcing unless you got a little oil on them. Try cleaning them off with some alcohol & recheck them to see if they're still arcing. Also if they're arcing at the either end, then make sure your boots & caps are clean & the elect portion of the connectors are pushed in & on all the way. Same with the boots & caps. Anywhere you see an arc, there's a problem.

* Smth else, pull your dist cap & look inside. If the moisture & humidity is affecting your wires like this it could be getting inside the cap too.
Sorry Stephen the new wires are fine and the cap shows no signs of moisture.

Thank you for the reply
 
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