If your engine speed signal drops out randomly right after installing a new crankshaft position sensor like the tachometer flickering, the car stalling at idle, or the check engine light flashing code P0335 or P0336 you’re not dealing with a faulty part right out of the box. You’re likely facing an installation-related issue that’s interrupting the signal path. This isn’t rare. It happens most often when the sensor isn’t seated correctly, the air gap is off, or something in the wiring wasn’t reconnected cleanly.

What does “intermittent engine speed signal missing after sensor installation” actually mean?

It means the engine control module (ECM) is receiving the crankshaft position sensor signal only sometimes not continuously. The ECM needs that steady pulse to time fuel injection and spark. When it drops out, even for a fraction of a second, the engine may hesitate, stall, or refuse to restart until the signal returns. Unlike a total failure (which usually sets a hard fault and won’t start), this one keeps running but unpredictably.

Why does this happen right after installation and not before?

Because the old sensor was likely failing gradually, and the ECM had adapted or masked some glitches. A new sensor exposes underlying issues the old one had been working around: a slightly damaged connector, a frayed wire near the harness grommet, or corrosion inside the mounting bore that changes the air gap when the new sensor is tightened. You can see this same pattern in vehicles with rough idle symptoms before replacement, where the problem seemed resolved until the new part went live.

What are the most common mistakes during installation?

  • Tightening the sensor too far, compressing the O-ring or shifting the air gap beyond spec (usually 0.020–0.060 in / 0.5–1.5 mm depending on make)
  • Forgetting to clean metal shavings or debris from the crankshaft reluctor wheel or sensor mounting surface
  • Using a non-OEM sensor with different internal resistance or output voltage, confusing the ECM’s signal interpretation
  • Leaving the connector partially seated or mistaking a secondary lock tab for fully engaged
  • Routing the new sensor’s wiring over hot or moving parts, causing chafing that only shows up after vibration builds

How do you test for this without guessing?

Start with a visual and physical check: unplug the sensor, inspect both sides of the connector for bent pins or moisture, then reconnect firmly listen for the double-click if it has a locking mechanism. Next, verify the air gap with a feeler gauge (not a coin or random shim). If the vehicle has high mileage, pay close attention to the wiring harness near the firewall or transmission bellhousing these are common wear points. A thorough wiring harness inspection procedure can catch insulation cracks or intermittent shorts that multimeters often miss.

Does mileage affect how this behaves after installation?

Yes especially on engines with over 150,000 miles. The reluctor wheel teeth can wear or crack, or the tone ring may have shifted on the crankshaft. That doesn’t always trigger a code with the old sensor, but a more sensitive new one will expose it. In those cases, replacing the sensor alone rarely fixes the intermittent signal. You’ll need to inspect the tone ring and consider whether the crankshaft itself needs attention. We’ve seen this repeatedly in older Honda K-series and GM LS engines, where the tone ring slips just enough to cause dropouts under load. That’s why replacing a crankshaft sensor on a high-mileage vehicle often requires extra steps beyond the standard swap.

What should you try first?

Before buying another sensor or scanning deeper: • Re-seat the connector and confirm full engagement • Measure and adjust the air gap using the factory spec not the old sensor’s position • Check for voltage at the sensor connector with the key on (should be ~5V reference, ~12V power, and a solid ground) • Wiggle the harness gently near the connector and along its route while watching live data for RPM signal dropout • Look for oil or coolant contamination on the sensor tip it can mimic electrical failure

If all those check out and the signal still drops, the issue is likely upstream: a failing ECM input circuit, damaged tone ring, or internal harness fault. But in most cases we see, it’s one of the first three items above especially the air gap or connector seating. Don’t assume the sensor is defective until you rule those out.