If you guys have V8 miatas and wonder why the engine occasionally tries to stall while coasting or at clutch disengage (especially when engine braking is done), the likelihood that your ECU is not receiving speed data from the speed sensor that the speedometer cable is connected to. The Vehicle Speed Sensor (VSS) has two connections: mechanical and electrical. The mechanical goes to the speedometer on your dash. The electrical goes to the pin 3 (+) and 6 (-) of your ECU. The lacking of the VSS contributes to the ECU depending on other sensors to compensate for return-to-idle RPM/load tables and when to re-open injectors. The complications is a result of emission directives set forth by the U.S. Government.

Eliminate idle issues by making sure your VSS is connected.

A good guideline to help fix your idling issues on Stangnet.

I made my own harness by using the ECH EC139 vehicle speed sensor pigtail acquired from NAPA for $9 and some 16 gauge green/orange wires and some wire loom. Be sure to ground the harness to pin 6 wire in between.

When doing this, be sure to have the base idle set at 600 RPMs (IAC disconnected) and adjusting the idle screw until the RPM reaches 600. Then disconnect battery and leave disconnected for 15+ seconds to reset the ECU. Reconnect the IAC valve then reconnect battery. Start motor. See how it idles then.

This entry was posted on Sunday, November 29th, 2009 at 8:39 pm and is filed under Main, Modifications. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.