Experiencing a frustrating bouncing idle or idle surge in your 1990 Honda CRX? You’re not alone. Many CRX owners encounter this issue, often indicated by a P0505 engine code (idle system malfunction). Before you start replacing sensors and spending hundreds of dollars, let’s explore a less obvious culprit and how a scan tool can play a role in diagnosing the problem.
Many mechanics, when faced with idle issues, might immediately suspect components like the Idle Air Control (IAC) valve, MAP sensor, EGR valve, or even oxygen and throttle position sensors. While these can indeed be the source of problems, sometimes the solution is far simpler and less expensive. One often overlooked cause of idle surge, especially after work has been done on the engine, is related to the throttle body itself.
The Hidden Issue: Throttle Body Paint
Here’s a crucial tip for 1990 CRX owners and mechanics working on these vehicles: avoid using carburetor cleaner aggressively inside the throttle body. Why? Because Honda, in their original design, applied a ring of paint to the back side of the throttle plate and the throttle body walls. This paint, often mistaken for dirt or carbon buildup, is essential for maintaining the correct idle by precisely controlling airflow around the throttle plate.
If this paint is inadvertently removed during cleaning, it creates excessive air leakage around the throttle plate. This extra air throws off the idle control system, leading to the dreaded idle surge and potentially triggering the P0505 code.
Fixing Idle Surge Caused by Paint Removal
So, what if the paint is already gone? Here are a few solutions, ranging in complexity:
- Minimum Air Screw Adjustment: Locate the minimum air screw on your throttle body. Carefully adjust this screw in small increments to reduce the extra airflow until the idle surge stops. However, this may not be effective if a significant amount of paint has been removed.
