Your 2021 Mazda MX-5's engine idles roughly or higher than normal once warm, and P0507 confirms the Engine Control Module is detecting idle speed above expected range. An unsteady or elevated idle in the spirited Miata detracts from the driving experience. Let's find the cause and restore smooth operation.
Understanding P0507
P0507 sets when the idle speed exceeds expected values by more than a specified amount (typically 200+ RPM). The ECM controls idle speed through the electronic throttle body—when actual idle is higher than commanded despite the ECM's efforts to lower it, this code appears.
The "rough" part often comes from the ECM's attempts to correct the high idle. It closes the throttle further, causing the engine to stumble, then compensates—creating an unsteady hunting idle.
Common Causes
Vacuum leaks allow unmetered air into the intake, raising idle speed beyond the throttle's ability to compensate. The ECM can't reduce airflow below what's leaking in.
Dirty throttle body creates inconsistent airflow past the throttle plate. Carbon buildup around the bore prevents proper low-speed air control.
Idle air control issues in the electronic throttle system—worn throttle motor, position sensor problems, or throttle body malfunction—prevent accurate idle control.
PCV valve problems introduce extra air through the crankcase ventilation system. A stuck-open PCV allows too much airflow.
Intake manifold gasket leaks create large vacuum leaks that raise idle speed significantly.
Diagnostic Approach
Test for vacuum leaks first. Use a smoke machine or propane enrichment to find leaks in vacuum hoses, intake gaskets, PCV system, and brake booster line.
Clean the throttle body. Remove the intake tube and use throttle body cleaner on the throttle bore and plate. Carbon buildup here is common and affects idle control.
Check for additional codes. P0507 often appears with codes for MAF sensor, throttle position, or specific misfires that provide direction.
Monitor idle air learning parameters with a scan tool. The ECM's idle corrections reveal whether it's fighting extra air or struggling with throttle control.
MX-5 Specifics
The Skyactiv 2.0L in the MX-5 uses a relatively high idle (around 750-800 RPM) by modern standards for a sporty feel. However, P0507 indicates speeds significantly above even this baseline.
The engine bay is compact with limited service access. Vacuum lines and connections can be difficult to inspect thoroughly without removing covers.
Repair Costs
Throttle body cleaning: $100-$200 including labor, or DIY for $10-$20 in cleaner.
Vacuum leak repair: $50-$200 depending on which component leaks.
PCV valve replacement: $30-$100.
Throttle body replacement if internal failure: $300-$600 including labor.
Intake manifold gasket: $200-$400.