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This car has ran rough since I got it, its fine at driving rpms, but when you stop it idles rough, its died on my a couple times. there has never been a check engine light on unless I unplug the Intake Air Temp sensor. I used the key on/off sequence and It comes up with a P0113 code which means low IAT circuit input, I tested the two wires going to the sensor with a volt meter and it shows 76.x MV going into the sensor. From what Ive read theres supposed to be 5V. So i dont know what to look for next? it seems the sensor isnt even working with that low input but at the same time if I unplug it it sets the check engine light.. so it must be working right? any idea where to go from here?
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Let's clear things up a bit here. A code of P0113 means the computer is sensing a voltage from the sensor that is too high. (P0112 is the error code for voltage that is too low.) The way the sensor works is that it's a thermistor, that is, as temperature of the intake air changes, the resistance of the sensor changes. As temperature increases, the resistance decreases. The computer sends a 5v signal through the sensor, and reads the voltage of the return signal. It should fall in an expected range, based on the expected resistance of the sensor. If it falls outside of that range, either high or low, an error code will be set.
The return voltage is outside of the range if the resistance of the sensor is outside of its expected range. The long and short of all this is that your IAT sensor should be replaced. That should eliminate the error code and could very well clear up your rough idle as well, but I would very carefully check for vacuum leaks and would consider new spark plugs too.
But the code means there isnt enough power before the sensor doesnt it? no one has the sensor they have to order it from the manufacturer and I dont want to replace it if its not the problem you know..
The sensor gets its controlled voltage from the engine computer. If that's bad, you've got bigger problems. Check the wiring leading from the sensor to the computer. The wires will disappear into a wiring harness but the same wire color comes out at the end.
Remember, the computer is concerned with a voltage difference reflecting a drop across the thermistor, not an absolute value.
Check for a vacuum leak too, and check the spark plugs.
Alright im going to test it again with a volt meter this afternoon to be sure. when the cars running if i unplug the sensor and find a solid ground in the engine compartment and put the pos lead of the meter to the plug which has 2 prongs there should be nothing on one prong and 5v on the other right?
I changed the plugs last week.. I used autolite platinums which I know i shouldnt use but it didnt change the way it ran at all. the motor was rebuilt 6 months ago so all the tubing and everything is new also. Ill check tho
The Black/red wire should be the signal voltage from the computer. The black/light brown wire should be what's called "signal ground" which is not necessarily the same as engine ground. You could check the IAT sensor by measuring its resistance at different temperatures to see if it changes appropriately.
Alright Ive been busy so I havent had time to check it til yesterday night. I took the sensor out after the car was running for a while and it was hot. Resistance was 5k ohms. then I let it cool down a minute and checked again and it was at 8k ohms. I checked again about an hour later and it was at about 10k ohms at room temp. then I checked my codes again today and its reading out 112 and 113 i guess before i just didnt give it enough time to read both. SO im thinking the sensors good?