It all started when the motor would run at a higher rpm while backing off the throttle and when coming to a stop the motor would not drop to idle until the car completly stoped. It has a rich condition, but runs ok. When i stick my foot into it runs very good. I have a o2 gauge and it does not sweep very far into the lean. I have modify the engine and put a tune into it and it help the rich conditon to some extent but because of the response of the higher idle and dropping to the base idle when completly stoped, i am leaning on the speed sensor as the culprit

Did any of your modifications include changing the cam? If not, you might want to look into the Idle Air Control Valve on the throttle body. They can cause a problem like this.

Today i did check the speed sensor and it is good, so i checked the iac valve. The voltage going to it was fine and the carbon deposits were very thin, thats because of the milage. So my next thought would be that the solenoid may not be controling the pintle. The excessive amount of air if this is true would be telling the o2 sensors that there is abnormal amount of oxygen in the exhaust stream and it would be giving the pcm to enrichen the fuel. That may be why i am running rich, and at idle it smells and i did not as of yet change cams. I changed the heads,exhaust, plenum, throttle body, msd dis4. I checked the termanals on the iac and there was readings but i have no way to know what the readings should be if there is any. I do not like to throw money at replacing this with out more knowledge, but this makes sense

Is the check engine light on at any time?
There are many reasons for an engine to run rich. Among them is an inoperative/stuck O2 sensor, intake air restriction,incorrect inputs to the PCM, incorrect outputs from the PCM, misfires,bad injector(s) to name a few. It's time to get a scan tool on that engine and see what is happening with the engine data like fuel trim , O2 activity and IAC counts% . Can you get one and obtain some of that info?

The check engine light is not on and i do have a scan tool, since i changed the heads and so on that a tune was needed. Like i sayed the tune did help, so i thought it would be easy to diagnois it with out hooking it up but i guess i will hook it up and check it out once again

I found the culprit with the multimeter. The signal wire from the maf sensor had no voltage at idle or off idle, replaced the sensor and the fuel trim is responding like it should be

Good job ! Stay in touch, there are lots of folks on this site that could benefit from your knowledge.