Misfire after using automated car wash

[JRD]

I took my new to me 05 Chevy ecsb 4x4 through the automated car wash, and shortly after I passed over the underbody spray it began to run very rough, and check engine light began flashing. On way home it smoothed out. The code it throws is P0300. Random misfire. I looked under the engine and all around engine bay for loose sensors or to see if the wires or coils looked like they had breaks to allow water in easily.

Question is has anyone else had this happen, or what would most likely to be getting wet and causing this? I have always washed my trucks this way in winter and never had that happen. Could be a fluke.
Thanks in advance.

 

[Longshot270]

Water shorting the coils out. I've heard of the Fords doing it also when people power wash the engine.

 

[Draenor]

How old are the ignition wires? I'd change them out first. Sometimes they get brittle and get cracks, enough to let water in.

 

[OldCracker29]

If you live in Ohio, chances are you have some brittle wires and the under body spray was just enough to screw shit up. I'd bet you could clear the code and it wouldn't come back on after the wires had a chance to dry out. I'd still recommend changing the wires like John mentioned.

 

[Zembonez]

I agree with the others. Age has eroded a watertight wire or plug to the point that it allowed water in. Hopefully it will dry out and fix itself.

 

[JRD]

Thanks for all the input guys. Turns out my wires were extremely brittle. They all broke as I removed them. New plugs, new wires, just need to clear code.

 

[Black02Silverado]

Glad you figured it out. Spark chasing can be a nightmare!

 

[stealthperf]

Might not hurt to put a little dielectric grease on the inside of the wires... It helps to seal the boots to the plugs and coils and make things even more water tight.