Casper’s IAT Resistor Mod

by Scott Brock

Copyright 1998





This modification is cheap and easy. I use it often in bracket racing to tune the car to a given dial-in. During a dyno session test we pulled a max of 7 rwhp extra with the mod, with the average between 4 and 5. The car at that time was a 98 Cobra with a B&B tri-flow cat-back, K&N replacement filter in the stock airbox (minus the snorkel), NGK TR5 plugs gapped at .054 and a bottle of 104+ black label in a full tank of premium. Each run was preceded with a 30 minute cooldown with the battery disconnected. The only dyno scan currently available was not the best run of the day (we made 12) but it does show the little "blip" of extra power around 4800 rpm. Maybe some of you dyno junkies can come up with some more data:

A sample dyno run with the mod:




As you can see it was hot and humid. We tried it also on a 97 that day but it kept losing power. He also showed some strange dips on the dyno graph in random locations which we assumed were fuel related. He had several thousand miles on the fuel filter, and he had ram air, BBK throttle body and pullies. More data is needed to say this is a 98 only mod, but it seems to work well on mine. I always run it at the track with race gas or octane booster, and a 30 minute battery disconnect. I feel it gives me just enough to pull a really difficult dial, and keep it in my bag of tricks. I consider it worth 0.5 – 1.0 mph in the mile. I don’t see any need for it on the street, as the computer "learns" your trick in a very short time, and adjusts accordingly, often hurting performance until the next battery reset.


To begin, you need a roll of electrical tape. Every stanger has some in the glovebox, right? You also need some resistors. I use 100k ohm watt resistors from Radio shack.

Casper’s choice of resistors



The IAT is a thermocouple which increases in resistance as it gets colder. We want to fool the compets colder. We want to fool the computer into thinking the IAT is reading 100k ohms, and adjust the timing and fuel for a very cold intake air temperature, like on a 10 degree winter day.

Locate the IAT sensor. It is in the air intake tube, near the passenger fender and behind the MAF. It lookes like a little plug with two wires coming out of it.

Casper points out the IAT location

Closeup of the IAT location


You will need to grasp the edge and squeeze the clips as you pull on the plug. It should pop right out of the IAT. If the whole thing comes out of the tube, just disconnect the IAT from the plug and stick it back into the hole. You must keep this hole covered or you will have a vacuum leak. You will be inserting the dummy load (the resistor) into the yellow plug end.


The plug end where the resistor goes


Now get your resistor ready. I find it easiest to bend the resistor in a ‘U’ shape, especially if I plan on re-using the resistor.

plan on re-using the resistor.


Casper bends the resistor leads


Now carefully stick the resistor leads into the two holes in the end of the plug. Push them in so they make good contact with the metal but don’t jam them. And don’t use a bent up old resistor, as the leads may break off. At 10 cents apiece, why take a chance?

Inserting the resistor


Once you have it in, bend it over and cover it with a couple pieces of electrical tape.

Cover the ends with tape



And then just leave it hanging loose. Don’t forget to reset your battery. I often wait till I get it over to the staging lanes to do all this, so that I get a fresh computer at the staging line.

Just leave it hanging loose


You may not get anything out of this, but I have plenty of faith in it. hing out of this, but I have plenty of faith in it. So much so I always keep a few resistors in my hat. You never know….

Casper’s racing hat


Later gator, Cya at the Plex!