Why Does Your Car Run Poorly in Moist Conditions?
Intermittent problems can be a challenge to diagnose even for experienced technicians. When you have an issue that seems to come and go, the first step is usually to ascertain under which conditions it appears. Moisture is a common trigger for many automotive problems, and you may experience poor running conditions on humid days or after a significant rainstorm.
While it's never fun to experience issues with your car, noting when the problem occurs can be a great way to understand the underlying cause. If the problem seems to center around moisture, then it may be the result of one of these three causes.
1. Cracked Wiring Harnesses
Your car relies on several essential sensors to run correctly, and each sensor uses a wiring harness to supply power and report readings back to the ECU. These harnesses are typically shrouded in plastic insulation, which can become brittle and crack over time. When the harness fails, water can reach the wires and cause shorts.
Shorts in a wiring harness can cause sensors to fail prematurely or report inaccurate readings, ultimately leading to rough idling, poor acceleration, or reduced fuel efficiency. Commonly affected sensors include the O2 sensors and cam or crankshaft position sensors. If you have an intermittent check engine light that only appears after rain or in damp conditions, then one of these parts is your most likely culprit.
2. Bad Spark Plug Wires
Depending on the configuration of your vehicle, you may have spark plug wires that carry voltage from your ignition coil to each spark plug. As with the wiring harnesses for your sensors, these wires can wear out over time. Because of their importance and tendency to wear out, many manufacturers recommend replacing spark plug wires at regular intervals, often once every 100,000 miles.
3. Ignition Coil Problems
Many newer cars use a coil-on-plug design, with each individual cylinder having its own ignition coil. These coils rely on making a tight seal with the top of the cylinder, and any failure can result in ignition problems. If the insulation on the coil has failed, then moisture can cause a short or even leak down to the spark plugs.
As a general rule, ignition problems are usually the cause of rough running in wet conditions. Although lousy spark plug wires and ignition coils are the two most common culprits, problems can also exist with the distributor or other components in the ignition system. Because these systems use high voltage and are essential to the proper operation of your vehicle, always have them diagnosed by a professional who can perform any needed car repair services.