I drove my 8 to my parents house in Michigan (I live in Nashville), and on my way back I lost amost all of my power and had to floor it in 6th to maintain 70 mph. I made it back, and had a new MAF shipped to me. When it came in, I swapped it in and it worked fine for about five minutes, and then the car completely stopped idling at all and stalled if I let off the gas. I took it home and towed it back to Michigan, and I swapped out the throttle body for a new one. That worked perfectly for about a day of just driving around to diffrent shops with my mom, but when I was going home the car didn't start right away, and struggled to maintain idle before outright stalling when it warmed up. The check engine light also came back on with the trouble code "engine too lean". Now it periodically stalls when at idle, and struggles to get itself in the correct place. It idles at about 700 rpm and vibrates the entire car. Other than that it drives perfectly fine. Any ideas?

 

When was the last time you switched out ignition? Do you have a cat converter? When was the last maintenance? Do you have any mods? Auto or manual?

 

Keeping the Engine at an Idle
• Ignition Coils
• Spark Plugs
• Spark Plug Wires
• Engine Compression
• E-Shaft Sensor (ESS)
• Mass Air Flow Sensor (MAF)
• Front O2 sensor
• Catalytic Converter (Cat)
• Intake Vaccum

 

I strongly urge you to take the car to a Mazda dealer (or any good rotary mechanic) and let them diagnose the problem. Otherwise you can easily end up with a still unfixed car and the bill for numerous, expensive replacement parts that didn't fix it. "Playing" mechanic by throwing replacement parts at your car is a common mistake.

 

fuel pump?

 

Possible bad MAF sensor, but that usually throws a code. I think you diagnose point by point on what can cause bad idle. Diagnose before throwing parts at it.

Keeping the Engine at an Idle
• Ignition Coils
• Spark Plugs
• Spark Plug Wires
• Engine Compression
• E-Shaft Sensor (ESS)
• Mass Air Flow Sensor (MAF)
• Front O2 sensor
• Catalytic Converter (Cat)
• Intake Vaccum

 

Could a stuck secondary shutter valve cause this?

 

The secondary valve comes into play at much higher rpm than you describe your problem. More likely the primary intake valve.

Engine Power Loss
• chokes as revs increase
o O2 sensor failure (too rich)
o MAF failure
o MAF disconnected
o e-shaft sensor fouled
o accessory belt fraying
• high end power loss (hard fuel cut)
o Rev limit reached
• high end power loss (jerky and stumbling)
o Ignition failure
o fuel pressure loss
o e-shaft sensor fouled
• high end power loss (smooth)
o Catalytic converter clog
o air filter clog
• low end power loss (smooth)
o Engine compression loss
• low end power loss (stumbles)
o Ignition failure
o front O2 sensor failure
• revs slowly but smoothly
o O2 sensor failure (too lean)
o catalytic converter clog
o air filter clog
• sudden power drop at a specific rpm********
o Intake valving actuation problem
• trouble getting to redline
o Ignition failure
o front O2 sensor failure
o catalytic converter clog
o air filter clog
o e-shaft sensor fouled
o fuel pressure loss
o MAF failure

 

Assuming O2 sensor readings are reliable, a lean mixture indicates there is too much air in the exhaust stream. You may have a vacuum leak somewhere or you may have a problem with fuel delivery.

I would first suggest getting the engine compression tested. If compression is good, consider going to a mechanic with a high end diagnosis computer which can test all of your electrical system components from inside the car. I was able to borrow one for my car and within minutes I discovered a bad ps module, passenger side air bag wire fault, and that my VDI valve solenoid was bad.