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Hey everyone. So I have a 66 mustang that I put a 94' SN95 motor in. I am however using a DA1 (87 federal emissions) computer to run it on speed density. Now everything thus far is working except that I have a high idle. Now I have not been able to take the car out for a road test to see if the computer "learns" and adjusts the idle, so everything I have done is just running it in the driveway. KOEO I do not get any related codes. I get a few for emissions but I dont have them installed. KOER I just get the code telling me I have a high idle. I have set the base idle speed to 750 rpms and it will run like that all day until I plug the IAC valve back in and it takes over shooting the RPMS up to 1200. I am using the 94' TPS sensor, but with the throttle plate closed it is reading .95 volts. I originally had an IAC from a 87 speed density car thinking that the computer would be happiest with a same year sensor, but idle was high so I changed it out with a new one from the parts store, same thing. I took one out of a known working car, same thing high idle. So I tried a IAC from a 94 to match the motor and it ony made the difference in that my idle rpms would fluctuate like the computer was searching for the correct idle, whereas before they were stable but high. the fluctuation would be from 1200-1400 rpms. Same story, if unplugged it the RPM's would drop to 750. I have cleared the computer KAM each time and then letting the car idle for about 20 minutes for the computer to relearn the idle. Im at a bit of a loss of what to try next. I have checked and rechecked for vacuum leaks. Any ideas?
 

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Just some guy
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A faulty engine coolant sensor/connection can tell the the PCM it's cold all the time and the PCM will jack the idle up. Do you have some way to view live data or just codes?
 

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Discussion Starter #3
No unfortunately I’m using the paper clip method. I tested my ECT sensor. I have 4.7 volts at the plug and around 39.3 Kohm at 65.8° and 5.2 Kohm at 157°. So it’s in spec for both cold and hot temperatures.
 

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Just some guy
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It gets tricky without a datastream. Basically the computer is seeing some reason to tell the IAC to raise the idle. Next most common culprit I guess would be the TPS. Pretty easy to check one with a multimeter.
 

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65 Fastback 289 4 spd, 65 convertible 5.0L 5 spd. 3.73 8.8
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Hey everyone. So I have a 66 mustang that I put a 94' SN95 motor in. I am however using a DA1 (87 federal emissions) computer to run it on speed density. Now everything thus far is working except that I have a high idle. Now I have not been able to take the car out for a road test to see if the computer "learns" and adjusts the idle, so everything I have done is just running it in the driveway. KOEO I do not get any related codes. I get a few for emissions but I dont have them installed. KOER I just get the code telling me I have a high idle. I have set the base idle speed to 750 rpms and it will run like that all day until I plug the IAC valve back in and it takes over shooting the RPMS up to 1200. I am using the 94' TPS sensor, but with the throttle plate closed it is reading .95 volts. I originally had an IAC from a 87 speed density car thinking that the computer would be happiest with a same year sensor, but idle was high so I changed it out with a new one from the parts store, same thing. I took one out of a known working car, same thing high idle. So I tried a IAC from a 94 to match the motor and it ony made the difference in that my idle rpms would fluctuate like the computer was searching for the correct idle, whereas before they were stable but high. the fluctuation would be from 1200-1400 rpms. Same story, if unplugged it the RPM's would drop to 750. I have cleared the computer KAM each time and then letting the car idle for about 20 minutes for the computer to relearn the idle. Im at a bit of a loss of what to try next. I have checked and rechecked for vacuum leaks. Any ideas?
Usually is a vacuum leak with what you are describing. I luckily have a smoke machine that I use at my shop to ck. for vacuum leaks. I am not sure you can run that computer with a 94 SN95 engine. To ck. the IAC to see if it controls the idle just unplug it and see if idle changes. IAC usually doesn't cause drastic changes. Ck. to see if your idle stop screw has been messed with, if someone turned it in to open the throttle it will let a lot of air past throttle blade which will cause this.
 

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Just some guy
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We kind of hope that a full year on he's fixed this. Even though he never came back to say.
 
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