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.

I just upgraded the rear brakes. Same purpose and reason as of the front upgrade.

A bit more braking capacity would be nicer… now I have that and now everything is all dandy.

Click here for the rear brakes’ 90-93 to 94-97 upgrade procedures.

I spent some time to produce the front brake upgrade procedure for a 90-93 to a 94-97 brake set-up.

Click here to go there.

I will be working on the rear procedures. Should be equally as easy because the calipers are interchangeable. That’s the big plus. Why go up to Brembo or Wilwood’s for $1500+ when you can do the entire thing for $300 and have approximately as good braking capability. The Wilwoods are up to about 11″ which isn’t that much different than the 10′s that the 94-97′s have.

The 90-93′s did well for my driving habits with this car which is a bit aggressive and beating on it a few times here and there. For a few times, the 90-93′s brakes weren’t adequate for some functions that resulted in a few close calls and scares which prompted the agenda to upgrade them.

Hello V8 Miata enthusiasts, I’ve been driving around the Miata quite a bit working on the tuning of the motor a bit. For some reason, no matter what I do, I would find a sweet spot, then lose it. Kept getting the runabout every now and then. The following are the problems I was having all at the same time, or a solution to one creates another:

• Idle issues.  Stalling idles at cold starts (150RPM to 1000RPM bounces).
• Idle smoothens out at around 140°F water temperature, but when cruising and at clutch let-go for braking, the engine stalls.
• Engine power loss at a set timing that demonstrated a sweet spot of an earlier drive.
• The list goes on…

The following have been verified to be working correctly:

• Throttle Position Sensor (TPS) shows .945 volts at idle stop and responding correctly to adjustments
• Throttle Body is clean and sealed
• Idle Air Control (IAC) valve works fine (brand new)
• Vacuum is all sealed and steady when idle is steady
• Thermostat is opening/closing as supposed to
• MAF works fine and clean

Knowing that I addressed the fuel pressure issue earlier with a new pump.  The one thing I forgot entirely about was the fuel filter.  Duh!

Today, I went to AutoZone and picked up a new fuel filter and installed it.  After taking a spin for a little while… oh my God.  All the above problems are gone.  I came back to time the motor again.  I set it to 42PSI fuel pressure, 14° BTDC (advanced), and using the existing -8° camshaft timing (retarded).  The car hauls ass now – opened a new can of whoopass.  It runs very steady now, idles at 800 RPMs steady too.  Cold starts are steady now.

The retardation of the camshaft was intended to push the torque curve a bit later so I can get traction first.

Apparently the fuel supply was being constricted by an old filter.  The previous owner probably used the cheapest fuel that one could find.

So, folks, if you ever have the above problems, get the fuel filter out of the way.  A $20 fix.  If you’ve already done the fuel filter swap then you have another problem.