So wondering if anyone can help me out with my Mazda? I have ran the Diagnostics and codes P0507 & P0300 came up - the CEL comes on at start up. The RPM's start at over 2000 then as they are working there way back down at about 1500 or less, almost every time this happens the engine light comes on. The car runs perfectly fine and its been doing this now for about a month - I had it serviced and the throttle body cleaned out, and new spark plugs but that didn't effect it at all. Any ideas what this could be?? Thanks for any help!

 

Heres some information for you regarding both faults.

P0507, Idle higher than expected, The idle speed is controlled by fine tuning the idle speed control motor / or / throttle body motor (dependant on engine variant), to allow precise amounts of measured air into the engine, The most common causes below:

1. Vacuum leak allowing unmetered air into the engine
2. ISC / TB motor "actual" position not relative to "desired" position.

P0300, Multiple Cylinder misfire, The engine ECU, Monitors the engine speed throughout each revolution of the engine. It expects to see the engine speed either maintained or increased during specific crack shaft anges as each cylinder fires. When it sees : for example the engine speed drop throughout the range where Cylinder 2 should have fired - It determines that that cylinder "missed",

Multiple misfire fault codes means the ECU is unable to determine exactly what cylinder is "missing". This can be caused by (most commonly)

1. Multiple misfires (plugs, coils, mixture)
2. Multiple partial burns (plugs, coils, mixture)
3. Faulty Crank / Cam Angle Sensors (less commonly)
4. Corrupt engine speed signals (less commonly)

Given both codes are set it is likely that the issues are related.

-IE Unmetered air from a vacuum leak causing idle speed control issues and affecting combustion mixtures resulting in partial burns.

However, The first step i would undertake, is

Clear all fault codes and determine what conditions fault codes are set under
-Do fault codes set together ?
-Under what conditions ? (hot / cold)
-Do they reset immediately or only after a bit of driving ?


Regards,

Dayle Thomas OLCT
www.olct.co

 

Thanks for the response. That makes sense - i've had an issue with vacuum leaks in the past - after I replaced my transmission, however that was some time ago now. But the codes always come together and always when initially starting the vehicle. When it starts the RPM start at 2000 and while they are working down towards an idle of 1000 RPM or under, at about 1500 RPM - the codes will set. Very consistent.