Frankenstein car high idle issue - Vintage Mustang Forums
 
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post #1 of 4 (permalink) Old 02-27-2019, 06:12 PM Thread Starter
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Frankenstein car high idle issue

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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post #2 of 4 (permalink) Old 02-27-2019, 07:35 PM
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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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post #3 of 4 (permalink) Old 02-28-2019, 02:10 PM Thread Starter
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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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post #4 of 4 (permalink) Old 02-28-2019, 07:24 PM
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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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