The electronic throttle body on a Prius is quite easy to service, without
opening the coolant path that helps heat the throttle throat. Thus, no
need to drain and refill any engine coolant. The aim here is to keep all
the parts of the motorized throttle body well lubricated so it doesn't
stick closed, a somewhat common pattern problem on older cars.
These illustrations are from a second-generation '04, but the first-gen cars are very similar and the throttle body is almost identical. For reference and some design discussion, see the throttle body teardown and compare that assembly from an '02. In general, these units are about as beautifully simple as a throttle body can get -- one butterfly valve, a position sensor, and a few easy hoses. And the coolant line, which is perhaps the oddest thing about it but a completely sensible approach to prevent icing up in the winter. Far cry from the ol' four-barrel carbs with numerous bypass passages, needles, gaskets, floats, jets, diaphragms, screens, and a hundred other fiddly bits that we used to rebuild. Small pictures are linked to larger versions. |
The MAF and intake temp-sensor cable [green arrows] must be disconnected.
If you spaced and left the car powered up during this you'll get an
immediate error code, so obviously all this has to be done with the car
powered down. Slipping a small screwdriver into the slot in the grey cable
clamp will allow it to open easily and release the harness.
If you still have your intake snorkel [pink arrow], loosen the ring clamp bolt and slide the hose off the airbox flange. I don't even know where my clamp is anymore because that whole snorkel assembly has been OUT of my car for about five years now and I had to go find it just for the picture. | |
It's not even necessary to take off the airbox cover to remove the entire
assembly, but if you do watch your fingers when opening the one side clip
[red arrow]. The lower hinge of it can give a nasty nip if your finger
is next to it when unclipping. If you haven't inspected the air filter
in a while and at least knocked the loose dirt out of it, now might be
a good time. With proper care and occasional application of a vacuum to
the dirty side, the filters can last a very long time. At almost 160K
I'm on my second one, and probably could have stayed on the original.
Remove the two top 10mm bolts [yellow arrows]. The bolt underneath [curved yellow arrow] loosens another band clamp around the bottom neck of the air box. Now the whole airbox unit just lifts up off the throttle body flange. Note the construction of the collar that connects the two -- the hose clamp is specific to this application, and has a little alignment hole matching a right-angle tit on the rubber collar. Now would be a good time to clean and lubricate the hose clamp screw, because it tends to become corroded and stiff. Might be a convenient time to clean the MAF, too! |
Interesting ... there appears to be a little bit of cruft inside my TPS
housing. Well, it doesn't have a perfect seal and the
prior winter had
my whole engine bay possibly the filthiest it's ever been before getting
its routine hosing-out in the spring. But none of that got into the sensor
pot bearing, which still turns freely. This wants a gentle wipe-out with a
rag or Q-tip. Spraying anything into here is probably a bad idea.
Note that the sensor has its own independent return spring inside. |
Once everything's back together, test startup. You may have to clear an
error code anyway, if the TPS rests in a slightly different place than it
did before. This isn't a problem; the condition will self-clear and turn
the check-engine light off after four reboots of the car just like with any
other transient error, so you don't need a scantool to do that.
Going to Neutral during that first-minute warmup phase should not significantly change engine idle level -- it might bump up or down a little, but it shouldn't start revving or stumbling too far from its 1000-RPM or so baseline. If it does, you'll probably want to pull things apart again enough to realign the TPS. If you have *just* the right length of phillips screwdriver you might be able to do it in-place, but it'll be by-feel guesswork in a mighty tight workspace. Bob Wilson also offers some throttle service advice, using commercial cleaning products. I'm personally a little leery about such things when there's just not that much dirt to deal with, and would rather have the satisfaction of up-close component inspection instead of a relatively blind "spray-n-pray" approach. |