Chevy Prizm - Won't Accelerate Above 40mph in Heavy Rain/Snow

I drive a '98 Chevrolet Prizm with 205K miles on it. It drives perfectly fine except in heavy rain/snow. In those cases, I’ve noticed that as soon as I drive through a big puddle (i.e., get the undercarriage wet, it seems), my car won’t accelerate above 35 or 40 mph. If I attempt to push it faster, the engine (?) makes a terrible roaring sound, frankly like it’s going to die on me. Interestingly, if I pull over, turn off the car, let it “dry out” for a couple of minutes, and then restart it, it drives fine once again (assuming, of course, that I don’t hit anymore wet patches).

I first noticed this problem about 2 years ago during the winter when, on one occasion, it had just snowed heavily and I drove through a particularly sludgy patch on the highway. Since then, I’ve only had the problem recur a few times, typically during monsoon-like rains. However, more recently, I’ve noticed the problem wanting to occur even during medium-to-heavy rains. The car will start making growling noises in those wet conditions; however, if I keep pushing the car at highway speeds, eventually the sound goes away rather than crescendo-ing to the really scary roaring noise. I’m going to hazard a guess that by continuing to drive my car at highway speeds, even when it starts growling, it dries out whatever part is getting wet and thus getting “irritated”.

In sum, it sounds like my car is becoming more sensitive to and/or more exposed to moisture. Anyone have any ideas as to what’s going on?

More than likely, one or more splash shields are missing underneath the car, and this is allowing water to invade electrical/electronic components and also to cause the alternator’s drive belt to slip. I would suggest that you begin by replacing the spark plug wires, the distributor cap (assuming that it has a distributor), and the belt, and that you inspect the underside of the car on a lift in order to try to determine what might be missing.

However, you might have to compare your car to one w/o damage in order to see what is missing from your car.

Probably some ignition part. When it’s nice and dry and the car is running fine…then get a spray bottle of water and start spraying down ignition components one at a time til the car starts running badly. The last component you sprayed will be the problem.

I’d start with the plug wires, then the cap, and then coil.

When was the last time you had a tune-up?

Agree. Sounds like an electrical problem involving one plug. It gets worse before it gets better if left alone.

If under-the-hood spritzing with water doesn’t cause a problem, take a hose and spray the underside of the car slowly from front to back. It could be an O2 sensor plug that’s getting wet.

I agree with checking the splash guards since going through puddles causes it. Maybe soaking the alternator and belts.

Good advice above. Check for diagnostic trouble codes in ECM memory too. I might guess a crank sensor problem, since that sensor is often located where it can easily get splashed.

All great advice. Be sure to check the wheel well aprons too. The motor is transversely mounted, the belts and crank sensor just behind the right wheel well. If that apron is broken and water is splashing up onto the belt or the crank sensor, well…