Heres the deal... I made a log of a run and Kevin D. noticed a strange drop in my IAT reding while driving. As it turns out, it happens every once in a while when I have the throttle open. The readings hold nice and steady when the car is idling. I put a multimeter on the lead and noticed that the voltage would spike a few tenths of a volt at the same time the temps drop.

When I looked into it a little farther, I began to notice that my under 2K hesitation was always happening when the IAT reading would drop.

My question is - what would cause the IAT to get a voltage spike like it is?

It should hold nice and steady as it reads the air temp but I will have a reading of 90 F and once the throttle is opened, it will drop to as much as -40 F, then jump back up to 90 again.

I have the logs available to e-mail if needed and any help at all is greatly appreciated.

 

i wonder if that could be false readings and not actual sensor output. unplug the IAT and see what the temp defaults to.. if its -40* then you could have bad contact somewhere.

 

Seems like I read that someone on the board was having problems with their IAT giving funky readings only after it reached a certain temperature. Try replacing the sensor.

 

When its unplugged, it reads -40

The sensor was replaced in hopes of fixing the hesitation and it made it quite a bit better but it didnt solve it all - hence the datamaster runs.

Keep the ideas flowing


One thought - would it be possible to get a resistor that would simulate the ambient temp and install it between the 2 pins and see if the spike still happens? Im not sure if it would help or what resistance to try. The air temps here now are still in the 90's.

 

Back to the top for the day crew guys. Someone else is bound to have a idea about this...

 

If you replaced it with a new sensor and you are still having problems, its 10:1 that its a wiring problem. To eliminate the IAT sensor as the problem, use a resistor in the range of 3.5Kohms (68degF) to 2.2Kohms (86degF).

 

I will try to isolate it to either the sensor or the wiring with the resistor but do you know where the wiring for the IAT sensor leads to or a place where I can see a wiring diagram to start shooting the wires?

There might be a break in the wire somewhere but I dont really think so. I am almost leaning toward a PCM problem due to the spike in woltage. If it was a wiring problem, it would most likely drop in voltage, not raise.

Thanks for the input on the resistor

 

Rob/Shoebox has the wiring diagrams for a 95 on his website, including the PCM pinouts. The IAT part of the diagram will be the same for all years from 94-97.

Shoebox's Tech Pages

 

Good deal... thanks!

 

Fred -

I tried the 2.2K ohm resistor to bypass the sensor and it worked like a charm. The datamaster log was nice and flat and I didnt get any hesitation at all. It still needs a little more field testing with a new IAT sensor but at least I know what it was. Thank you for all your help... you da man!