I just bought a 94 touring and I noticed that the engine isn't running right. It revs just fine but as it falls back to idle it begins to stumble and at times it seems like it might die befor it stabalizes around 1000 rpm. Has actually died on 2 occasions. What could be a cause of this problem? I understand these arent interesting questions but the help is much appreciated, learning engines on a rotory engine can be difficult.

 

Could be 1 of 100 things mate ,Have u still got your air pump ,Some vac lines could be blocked , a sensor could be dirty , Rotary's are renouned for being rough idlers

 

When was the fuel filter last changed? If you don't know, start with that chore. It should be done much more often than Mazda suggests - I think 15k miles / 2 years is a good guideline.

If the filter doesn't fix it, check out things like the IACV, dashpot, and other little things near the throttle body. Section F of the Factory Service Manual has a troubleshooting chart that gives you a list of components to check depending on the idle symptoms.

Dave

 

Tps

 

Adjust the Idle Air Control located towards the bottom of the throttle body. You dont need to take off the elbow, all you do is take a small flat head screwdriver, feel around for an opening, stick the screwdriver in there rotate it until it catches on to the screw. Turn CC to bump idle up a bit.

Also, my FD used to die out because of it running rich at idle. You can adjust idle or decrease idle fuel a bit (if you have a Fuel Controller).

 

Does it seem to happen more when in gear at a stop? Could be the clutch switch (mine went out just recently, replacing it or fixing it solved 80% of the problems)

 

This seems to be a pretty common problem but no absolute fix. I had this happen to me and what I noticed is that the car will idle well but if you were to give her a quick rev in neutral the rpm would fall down a little bit too much, sometimes stalling. It may very well be your TPS adjustment but I didnt have to adjust mine, I cleaned out the TB, and changed my plugs and wires. People will say compression test your car (good idea) but my compression was/is fine.

 

Throttle position sensor (tps) out of adjustment, and/or replace clutch switch.

 

The standard "Miata" (forgive me please) idle speed adjustment seems to work well on our '94. Turn off the ignition, open the Diagnostic Connector. Locate the "TEN" and "GND" terminals using the label inside the DC's cover. Jumper the "TEN" terminal to the "GND" terminal (be sure to pick the "GND" location that actually has a terminal installed) and start the engine. (You can use a paper clip if no wires are handy.) If you can ever find the idle speed adjust screw (it took me about 15 minutes, but at least the engine was fully warmed up!), adjust it for an idle speed that does not change when you remove the jumper. That should be around 750 rpm.

The above is sort of basic, but it can frequently fix erratic idle speeds.