Truck runs terrible only when it rains

[wireman116]

My old 99 runs terrible only when it rains, but it runs great all the time?
Any suggestions? I would appreciate any help out there.Thanks

[bob harris]

Maybe get some sealant around your CPS ??

[atvrider93]

Does it still run bad if it's raining but the windshield wipers are off? If it's just with the wipers on change the cps

Sent from my DROID BIONIC against my will

[jesilvas]

Might have a windshield leaking onto the GEM or PCM.

[JJFLASH]

...don't drive it in the rain? just kidding.

You are gonna have a bad connection, cracked wire coating or something somewhere that is likely getting water in when it rains. Can you give some more detail? How does it run? Does it do it right from start up sitting in your driveway if it's raining or do you have to drive for a bit and get spray swirling around?

I agree that CPS/CPS wiring could be a likely culprit so I would put a new one in and inspect the wiring. After that, I would start your truck then use a garden hose to SLOWLY AND METHODICALLY pour water over your engine/wiring until the symptom starts, starting at your new CPS. Don't use a spray nozzle or something so the water blasts all over. Don't get excited and hurry. Soak a small portion then wait a minute cause it may take a bit for the water to penetrate. If nothing happens, move on to the next area and so on.

[NoRalPh]

The rain & CPS issue actually has Nothing to do with water, a wire, or a connection. IF you have this problem it's caused by the wiper motor that's generating something that interferes with the CPS's signal to the PCM. This only happens with certain wiper moters and certain CPSs in certain trucks. It's not Really common but not unheard of

Stumbles when it rains??

[JJFLASH]

Sorry, I should have said "if it's not the wiper motor issue then..." in my post.

[wireman116]

It starts stalling once I drive it down the road. It has died at a red light also. When it is dry without water it run great. I will try it without the wipers on next time it rains when I get going. Thanks guys I appreciate your time & help. Dave

[JJFLASH]

You can go try it with the wipers right now. If that's the issue water has zero to do with it and will act up.

[CT Performance, Inc.]

Its likely the IDM....check signs of water getting into the box or harness.