Why does the throttle cut out and not go past half-throttle after driving a few miles in a Mazda RX-7 FC?

Difficulty: Moderate

When an FC RX-7 runs fine cold but chokes, breaks up, or limits you to half-throttle after driving a few miles, you are usually dealing with a sensor issue that manifests once the car warms up (entering closed-loop fueling), a severe vacuum leak, or a failing electrical component heat-soaking.

Based on typical FC behavior and community consensus, here is how you should diagnose this:

1. Check for Post-MAF Air Leaks

The FC's engine management relies heavily on the Mass Air Flow (MAF / AFM) sensor. If unmetered air enters the intake tract after the MAF, the car will run extremely poorly and can cut throttle or stall out, especially under load ¹.

• Action: Inspect the corrugated intake boot between the MAF and the throttle body for cracks. These often split in the accordion folds where it's hard to see. Check all vacuum lines routing to the intake manifold.

2. Test or Swap the MAF (AFM) Sensor

A failing MAF sensor is a known culprit for partial-throttle fuel cuts on this platform. In a very similar case where an FC would cut fuel anytime the pedal went past 1/4 throttle, the issue was ultimately resolved by replacing the MAF sensor ⁴.

• Action: If you have access to a known-good FC MAF from a buddy's car, swap it in and take a test drive. If not, you will need to test the resistance values of your current AFM with a multimeter per the factory service manual.

3. Test the Throttle Position Sensor (TPS)

A bad, unplugged, or out-of-calibration TPS is notorious for causing mid-throttle hesitation and fuel cut on the FC ⁴. If the internal wiper in the sensor wears out at the halfway mark, the ECU suddenly loses the throttle signal and cuts fueling.

You need to perform a sweep test to verify the sensor's health.

• Action: Gradually depress the throttle pedal and watch the voltage change on a multimeter. You are looking for the numbers to climb smoothly. If they skip around, drop to zero, or spike, you either have a bad TPS or a wiring issue ³. It is also good practice to remove the throttle cable during this check to ensure it isn't influencing the reading, and physically inspect the throttle plate and linkage to ensure nothing is sticking ³.
• Note on specs: I don't have the verified factory voltage range for the FC TPS closed/open positions in front of me, so don't take a hard number from me on the exact calibration limits—check your Factory Service Manual for the specific baseline voltage. The sweep procedure itself remains the same regardless.

4. General Fuel & Spark (Heat Soak)

If the intake and sensors check out, standard diagnostic practice for a car that dies after 3-5 miles points to heat-soak.

• Fuel Pump: As fuel pumps fail, they overheat. Once hot, pressure drops, and the car will choke under load. (Note: Replacing the fuel filter is a good maintenance step, but it rarely cures this specific symptom on its own).
• Ignition Coils / Igniter: Coils commonly break down internally as they heat up in the engine bay, leading to weak spark that blows out at higher RPMs or wider throttle openings.

Start with the TPS sweep test and a thorough hunt for vacuum leaks, as those are free and cover the most common FC-specific failure points for this symptom.