91 Miata is sluggish

My '91 Mazda Miata (stick) was running very sluggish. My Mechanic told me the timing does not seem to advance fast enough to drive at low speed. He checked the sensors… OK No trouble codes. He manually advanced the timing beyond specs and it runs pretty well (but won’t pass Calif smog). He thinks it is a possible computer problem. Any ideas why the timing isn’t advancing?

in the old days I would have said it was the vacume advance diaphram, but now-a-days I would be more inclined to tell you to go get the codes read. I would not be at all suprised to find that the crank position sensor was faulty.

I spoke to my mechanic about your answer. He said that the “Allday” program listed no test procedure to check the crank position/cam sensor. It said that if there were a malfunction trouble codes would show. There were no trouble codes. However, he got to thinking that even though it is all one unit the problem could be between the two sensors. He is going to check the price of the unit for me. If expensive I will have my son look for a junk yard one and a ECU computer as well. (I hope I communicated his response correctly) Thank you for your response

dont throw any money at parts until you are sure of the cause, that is trouble shooting is more than just a wild ass guess from me.

My guess would be for a MAF sensor that is getting ready to die.
The MAF sensor, combined with the Throttle Position Sensor is what tells the ECU that you have stomped on the gas, and want to accelerate.

The TPS tells the computer what ignition timing it should use.
The MAF tells the computer how much air is getting sucked into the engine, and then it decides how much fuel to add from that reading.

If you can get a scan tool that can display the MAF sensor readings, you would be able to tell if the sensor is is outside of specs, typically by comparing the reading at idle vs the reading at 2600 rpms.


My mechanic tried putting a good MAF sensor on. It did not do the trick. I guess I am ready to apply for the $1,000 Calif Vehicle retirement program and find another car. Thanks for everyone’s help.