The first DIY project I wanted to post is an upgrade of my Jeep's throttle body.  The throttle body is a mechanical device that limits the amount of intake air that is provided to the engine based on the position of the throttle and various engine ignition parameters.  In short, when you put your foot into the gas pedal, the throttle body opens a plate to allow more air into the engine to match the increased amount of fuel, ultimately resulting in more power.

On my Jeep, the throttle body is somewhat restrictive.  It has lots of sharp corners and chamfers that restrict airflow.  This results in less-than-stellar throttle response (the time between mashing the gas pedal and the engine actually accelerating).  There's a shop in Minnesota ("The Fastman") that takes OEM Chrysler/Jeep/Dodge throttle bodies and bores them out and polishes the sharp corners to allow greater airflow.  They get excellent reviews, so I bought one.  The pictures below illustrate the process of removing various intake components to get to the throttle body, then replacing it.



The first step is to disconnect the positive battery terminal.  This allows the PCM (computer) to drain its capacitors and "forget" the air fuel ratio it's measured recently.  This way, the PCM will be forced to relearn the air fuel ratio when we're done, allowing the engine to immediately make the best use of the new throttle body.  The PCM would gradually relearn the air fuel mixture eventually, but why wait?



I'm too lazy to bust out MSPaint, so here's a picture of some other guy's (much cleaner) Grand Cherokee with all the parts already labeled.  The throttle body is hidden behind the resonator, so we need to remove the resonator first.  To get the resonator out, we also need to remove the air cleaner hose and the upper housing of the air cleaner box. 



Now we're ready to start tearing the intake apart.  The upper housing is held to the lower housing with thumb clips.  The cleaner hose is held on with a hose clamp, so all you need is a slotted screwdriver.



With the upper housing and the air cleaner hose removed, we can now pull out the resonator.  There are two 10mm bolts attaching the air cleaner to the intake manifold.  They are recessed underneath the resonator so I couldn't get good pictures of them.  There is another hose clamp attaching the rear of the resonator to the throttle body that also needs to be removed with a slotted screwdriver.  Finally, a vacuum hose is attached and can simply be pulled off.  The resonator then lifts out of the way.



Once the resonator is removed, the throttle body is now accessible.



Another vacuum hose is attached to the driver's side of the throttle body.  It can be a pain to work free.  Also, carefully remove the wire harness for the idle air controller (IAC) and throttle position sensor (TPS) using a T-20 Torx driver.  The idle air controller is a small electric actuator that controls airflow through the idle air bypass, which is the small "smiley face" opening at the bottom of the throttle body.  As the name suggests, this slot is used to allow minimal air intake into the engine while it idling and the main throttle body opening is fully closed.  It is easiest to leave the IAC and TPS attached to the throttle body for now and remove them once the TB has been removed from the intake manifold.




On the passenger side of the throttle body you'll see two cables.  The accelerator cable (attached to the gas pedal) is looped over a spring-loaded cam.  You can move the cam backward by hand, then pull the cable out of the slot.  The second cable, nearer the center of the TB body, is the speed control cable  The end loops over the top of a metal stud and might require some finesse to remove.  Once all cables and wires are detached, remove the three 8mm bolts holding the throttle body to the intake manifold.




The old throttle body was gunked up and filthy, but otherwise operational.



Here you can see the old and new throttle bodies side-by-side.  In addition to being much cleaner, the new throttle body has been bored out and machined to a very nice polish.  This is also a perfect time to move the idle air controller and throttle position sensor over to the new throttle body.



Here's the top of the intake manifold where the throttle body is mounted.  I really, really need to clean up my engine bay!  I was half-tempted to pull the intake manifold and clean it properly, but I decided to leave that for another day.



The new throttle body was so clean and shiny that I immediately regretted not scrubbing down the engine bay.  Mount the throttle body in the reverse order, bolting it down to 9 ft/lbs of torque.  Reattach the accelerator and speed control cables, the wiring harnesses for the IAC and TPS, and the vacuum hose.



Put the resonator back in place and reattach the hose clamp in the rear and the vacuum hose.  Curse yourself for forgetting to buy replacement vacuum line to replace the janky patched one you "fixed" two years ago.



Finally, reinstall the air cleaner hose and upper housing.  Curse again for forgetting to swap out spark plugs while you had the resonator off.  Remember to connect the positive battery terminal, fire 'er up, and go for a drive!


The only cost associated with this endeavor was the throttle body itself, which cost me $230 shipped.  The change in throttle response is really impressive, I can't believe how big a change was made with a little bit of boring and polishing.  It was definitely worth the money and I am still kicking myself for not doing this years ago!

I'm doing a complete brake overhaul this weekend (pads, rotors, calipers, brake lines, and wheel hub assemblies) this weekend which should prove to be an interesting experience.  I'll post those pictures sometime next week!


-b0b
(...POWER!)