Miss fire when it rains

Hey so i have a 2005 Colorado 5 cylinder, with the xtreme package.

When it rains i was getting a heavy rattle and a misfire. So i took a look had it in cylinder 5, and a gunked up throttle body. So i replaced all 5 boots and spark plugs, took the throttle body off and cleaned. It was aorking fine for 3 days, then it rained last night, i hit some real deep puddles, and how as soon as i turn it on it dies. Its not the battery, it starts runs at low rpm, clunks and shakes, then just straight up shuts off. I tried throttling it got it up to 3k rpm and it misfired again andbshut off. I have no idea whats wrong, the only other problem im having is the fuel cap light which is just the vent or valve (what ever its called) in the gas tank, was told its not a huge deal. Anyone have any ideas whats going on?

Edit: also i need to do an oil change but i did add oil and ik its got plenty of oil, just needs the oil changed

Welcome aboard, Mark!
You don’t say… How about that Check Engine Light… has that come on or come on and stayed on?
If so, it could hold a clue.


From what you describe about the trouble it makes me think the valve timing is off. Doing a compression test should help verify that. If the pressures are low that would be pretty good confirmation in my book.

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The check engine was on and is on. It has had the codes checked with a computer. Thats how we found the misfire, and the check engine will be on anyways since the gas tank has a problem.

Ill have to take a look at that, luckily my family are mechanics so i can see if what they think aswell. They were all busy or wasnt sure without getting a closer look at it.

If possible, it could help folks help you, if you’d post all codes in a P0xxx format.


Id have to go back and look thnx!

It’s difficult to diagnose some of these type problems with the vehicle at hand, but from cyber-space the codes would no doubt help.

There are a number of Chevrolet TSBs (Technical Service Bulletins) dealing with symptoms you describe, published by the manufacturer for use by Chevrolet technicians in solving tricky vehicle issues. That’s where the DTCs (Diagnostic Trouble Codes) come in to help match a TSB or TSBs with your DTCs and symptoms.

It possibly won’t solve your problem, but could point you in a more accurate direction to solving it.


Also, some of the 04-06 Colorado 5 cylinders had problems with the intake valve seats wearing and causing compression leakage resulting in misfire and eventual idle roughness, illuminating the Service Engine Soon light.

GM extended “special” coverage for some of these vehicles to 100,000 miles/7 years. That ship has already sailed.

There are other possibly pertinent TSBs.
Agree that a compression test should be part of a diagnosis.

Since new spark plugs and plug boots fixed the problem for 3 days, then w/rain the problem returned, I think you still have some sort of problem with the high voltage components in the ignition system. I presume you have coil-over-plug configuration, so likely a problem with the coils. Could possibly be a problem with the ignition module or crank position sensor too. If you post the actual diagnostic code numbers the scan tool reads from computer memory you’ll get more ideas here.

If this engine has a standard distributor with spark plug wires, I’d start by replacing the plug wires, the ignition rotor, and the distributor cap.

Since you seem to have a problem with the evap system too, good idea to experiment (as a test only) w/running the engine with the cap loosened. If that helps, perhaps a vacuum is developing in the tank, preventing the fuel from flowing to the engine.

If this trouble only happens during damp weather days I am going to have to rethink my thought of the valve timing being off. Like @George_San_Jose1 stated, I think the ignition system needs to be checked out further. Using a water spray bottle may help locate a weak point in the ignition wiring.