99 Mazda 626 2.0 has two codes, P0400 & P1506

I have a 1999 Mazda 626 with 2.0 4cyl auto trans. It drives good, but has a check engine light. I had it scanned and retrived the following codes P0400 (EGR flow) and P1506 (Idle Air Control System Overspeed Detected). For the EGR problem I plan on taking the EGR valve off and cleaning the carbon out of the EGR port and trying that before I replace the EGR valve.

When I bought the car last year the A/C wasn't working and I replaced the compressor. Running the A/C made the car idle really low and sometimes die, so I adjusted the idle at the throttle body. It has been running fine for a year, but could that of led to the P1506 code?

Any help appreciated.

The egr could be causing the idle speed code, so could the tampering with the throttle body though! You need to rest the minimum airflow to correct the throttle body or look for a used one that hasn't been tampered with! Be sure the egr is flowing properly through the ports before condemming the valve

Thanks Jeff,
The EGR was causing both codes. I removed it and inspected it. The valve was a little carboned up and wasn't moving smoothly. I cleaned it up and it moved really easy. I installed it, erased both my codes and drove around with my reader attached until all of the tests completed. It was good and I passed emissions.

is your idle speed to spec now?

Yes it is.

cool, congrats, glad I could help!