More questions and troubleshooting. Im having a weird idle issues. Whenever I start to slow down and let the RPMS drop to idle speed I get a hunting idle. I can be slowing down in gear and when RPMs get to 1k the idle jumps to 1200 several times. Same thing if I stop in Neutral. Voltage in TPS is in spec.

Does it a lot more when engine is cold. When engine is warm does it twice then idles fine. If im just idling in driveway it never does it. Only when coming to a stop when driving.

 

Does it happen when your lights and fan are on and stop when there off? Mine did that or similar and I cleaned up my grounds and stopped I also had vacuum leaks

 

Check the play and operation of your Dashpot per the FSM. It's the little round barrel on the throttle body. They wear commonly and can stick during motion.

Also check the play and adjustment of your TB butterflies per the FSM.

Does the car have a stock ECU?
Airpump?

 

No accessories are on at all.

Ill check that dashpot and the butterflies. Do I check the Double Throttle butterflies as well?

stock ECU
air pump
Completely stock car with fresh rebuilt, full premix, OMP delete.

 

Sounds like a sticky dashpot for sure. Best to replace it.

 

Yes, check the double throttles as well. They could be catching during decel. Go through the FSM and check all aspects of adjustment that are TB related.

No OMP on a stock ECU. I have little experience with the stock ECU, but doesn't this put it into limp mode or throw a CEL? I'm sure others can chime in.

Another possibility could be the clutch switch and neutral switch. The ECU uses these to enable the idle circuit. If you are stopped with the clutch pressed or in neutral the ECU enables the idle specific circuit. If one of these sensors fails, it can stumble around.

The neutral switch sensor is on the transmission. The clutch switch is attached to the clutch pedal assembly. Remember, the clutch assembly has two switches on it, one for the start disable, and the one for the ECU. The start disable is a small white switch closer to a visual glance. The ECU clutch switch is mounted higher to the clutch pivot point and is a larger sensor.

With a PFC, it would be easy to see if these sensors are working as it has a sensor screen on the Commander. With a stock ECU, you will have to pull them off and test them per the FSM.

 

Come to think of it it might be doing it mostly when I have the clutch pedal down. Ill check to make sure and ill check all the throttle controls.

Also I have my OMP plugged in while I have the stock ECU. Power FC is on my to do list after I take out the pre cat and get a new trans.

 

A simple test while driving, since you dont have a PFC.

As the car decels and rpm's drop, shift to neutral and release the clutch before 2500 rpm. See if the idle bucks. Then do the same thing but keep the car in gear with the pedal pressed. Whichever method causes the idle buck may need further investigation to its respective sensor and wiring.

 

I had no bucking driving it tonight at all. Couldnt get it to do anything. This morning however it was doing it. Ill test everything tomorrow morning thats on the TB.

 

I know im suppose to be doing the test while the car is warm but while its cold is anyones plunger this far in?

 

That plunger should stick out a good 3/4". That dash pot is bad. A new one is like $90 from Mazda. Grab yourself a new one.

 

Now it seems to be doing it a lot less haha. Heres another pic of the dashpot after I had been driving the car all day.

 

All the dash pot does is stop the throttle plates from slamming closed. If you rev the motor and instantly let off it slowly closes the plates to prevent an overly rich condition. If the dash pot plunger stick out as far as you show, there is not enough adjustment room left. You need a new one.

 

Okay just making sure. Never seen a new one or really knew what it does. Should I disconnect fast idle cam and doublethrottle while in there? I know thats something a lot of people do.

 

Because you're still on the stock ecu I would advise again removing those. I don't think the answer to problems is removing broken things. I believe it is fixing them. I have a new dash pot on my 7 but I'm out of town so I can't get you a picture. I am however 100% positive yours is bad. A new one from Mazda isn't too bad. I should have the actual price in my upkeep thread.

 

In agreement here. The fact that it is erratic does point to the dashpot as well. Sometimes sticking, and sometimes catching.