Throttle body cleaning tips?

listen to mr. wong, he won't steer you wrong.

 

Page 7 of the attached Toyota Technical Service Bulletin provides instructions regarding how to clean the Prius throttle body. Although this was written for Classic Prius (which is more susceptible to engine no-start due to a dirty throttle body and throttle plate) the same procedure is applicable to 2G Prius, which has the same basic engine design.

This throttle body cleaning procedure assumes that the car is IG-OFF, and there is no problem rotating the spring-loaded throttle shaft for access to the throttle plate underside. You certainly would not want to be cleaning the throttle body when the car is either IG-ON or READY.

Further, note that the instructions specifically recommend against flooding the throttle body with cleaner, contrary to the instructions that you might find printed on the throttle body cleaner can. The manufacturer of the cleaner wants you to use as much chemical as possible, while the TSB points out the damage which that careless process can cause to the throttle motor.

 

This article provides a simple explanation of three computer controlled systems that manufactures may employ, and goes into further detail if wanted:
Brake-by-wire, drive-by-wire (electronic throttle control), and steer-by-wire.

Someone correct me, but I believe the Gen2 Prius use drive and brake by wire.

 

ALL Prius throttle systems are electronic, "by wire" if you like. A quick examination of the throttle body will show that there is no mechanical means to connect the throttle to the accelerator pedal. That is why a throttle motor is attached to the throttle body, to rotate the throttle shaft.

The Prius throttle is particularly subject to requiring periodic cleaning because of the gasoline engine operating on Atkinson cycle. That results in valve timing such that the compression stroke starts while the intake valves are still open. Hence unburnt HC is forced into the intake manifold and eventually gunks up the throttle body interior and throttle plate.

Many engine designs do not require this cleaning because 1) they use the normal Otto cycle, and 2) the throttle is located far enough away from the intake manifold so that there is no reason for the throttle to get particularly dirty - unless there is an engine air filter failure due to poor maintenance.

The Prius braking system is also "by wire". Brake pedal movement provides information to a sensor mounted at the brake pedal. That tells the hybrid vehicle ECU what braking force is desired by the driver.

The HV ECU then decides how much regen braking to extract via MG2, and how much friction braking is required. The brake actuator assembly then sends the necessary hydraulic force to the wheel cylinders to effect friction braking.

If the Prius braking system fails, there is supposed to be a manual override for the hydraulic system, but based upon owner reports it appears this override is not very good. Hence you should count on significantly increased braking distances if the skid control system decides to fail on you. My dad actually experienced that fun as the first owner of the 2007.

 

As kind of an aside:
Don't panic just yet.
My Prius does some strange things with the engine every once in a while.
It rev's higher than normal when at a stop and does not do the "auto shutdown" thing like normal.
It doesn't happen often and I assume it is due to low traction battery or cold engine or some other unusual combination of factors.

If you aren't experiencing any other symptoms, I would surely wait until spring to do any TB cleaning......unless you have a well heated garage.

 

Chris don't forget to lubricate the big wrapped around spring on the end of the butterfly axle. Spray it good.

Get long 2 inch strips of t shirt cloth DO NOT use paper towel. While holding the throttle/butterfly open by by hand (turn the spring) shove the strip in as deep as you can past the open butterfly then soak the shite out it with carb cleaner. Still holding it open and with nitrile gloves on scrubby dub dub with the strip. Scrub the wall of the throttle body till it shines. SCrub both sides of the butterfly good. Pull it out and throw it away and repeat with more strips till its clean.

Take a good look at how corroded the edges of the round butterfly flap is. Thats where it will stick. While rotating the throttle spring look at that closely for issues. The little tb motor will not power through a sticky butterfly.

I also spray lube a tiny bit on where the butterfly axle goes through the tb walls.

And lastly there's is a throat clamp on the underneath of the ac filter box where the box fits over the tb throat. Have to get a 10 mm socket under there. Pain. It clamps the box to the tb. Make sure you tighten it down when your done or air will sneak past the air cleaner system.

 

Air will also be sneaking past the MAF, which will cause a lean mixture and performance problems. The two times I cleaned the old TB on my 2008 I used paper towel strips. I know, living dangerously. It's just that they are more maneuverable when way down there laying on the floor of the intake manifold. I have an extra long forceps to place and retrieve the strips and it gets rid of that curious liquid that accumulates down there.
A word on cleaning the throttle plate and spindle (or butterfly). Patrick has wisely cautioned any aggressive soaking of these parts. Solvent with a full load of carbon from your wash down can seep along the spindle into either the throttle motor or the throttle position sensor and gum things up there. Not good. But again, me living dangerously, I have used a folded piece of paper towel to act as a wick. I placed this on the underside of the spindle near the wall of the TB to draw the dirty solvent out of the joint. I only use small amounts of solvent and cycle the throttle a couple of times between extractions until clean solvent comes out. I know, extra cleaning of those parts was probably not worth the chance I took possibly fouling the electronics or causing a seized throttle. Dangerous stuff.

 

Yeah air leak past MAF is bad car will be very unhappy.
Paper towels are disaster. With cloth T shirt don't need forceps and can soak away.

Its very easy.

 

Would you guys recommend cleaning the MAF while in there?

 

Yes, remove the mass air flow sensor from the air cleaner housing, and spray out the sense wires and amber bulb with MAF cleaner.

My personal method to clean the throttle body is to use 91% isopropyl alcohol and Q-tips to swab out the throttle body interior and throttle plate. No worries about debris left behind or excess cleaning fluid going where it should not. Since my method is not recommended by Toyota, use it while applying your judgment and at your risk.

 

Unnecessary at 62K miles. Wait until you get to 120K miles, then you can replace the PCV valve at the same time as the iridium spark plugs.

 

Agree with Patrick. When you're doing the plugs at 120K you have the wiring harness over the valve cover loosened and this will allow pretty good access to the hidden PCV valve on the right (facing) side of the engine. That is when I did mine on my '08. Even then, the PCV sounded (rattle-rattle) clean. Of course you will be using MAF cleaner to clean your MAF. It is easier to clean when it is removed (two phillips screws) and then you can check the integrity of the O-ring around the MAF-to-air cleaner assembly fitting. A rough idle might be due to air incursion either at this seal or lower down where the air cleaner assembly clamps to the top of the throttle body. Hope you can angle the vehicle so you're working down-wind behind the hood.

 

I assume that is sweet corn.
I have inlaws scattered around Iowa but don't get up that way very often.

 

Giving this thread new life for the third time! How did cleaning your throttle body and MAF go, cyberpriusII?

I took my Prius to the dealer yesterday and they said "BG THROTTLE BODY SERVICE" and "CLEAN MASS AIR FLOW METER" were "recommended" but not necessary right now. (My car has about 47,500 miles.) I told them I am planning to drive cross country in a few months (moving from DC to the Bay Area, wooo!) and they said I probably wouldn't even need to have it done before then... I guess I appreciate their honesty and the fact that they aren't unnecessarily draining my wallet, but I think I'd like to take care of it if it would improve my cross country performance and save me money down the road!

So, question: I assume Throttle Body Service is just a cleaning? Should I contact them and make sure? If so, someone linked to these instructions in another thread: Cleaning Prius Throttle Would instructions for DIY on a Gen III be pretty similar? Also, I think somewhere on PC people said cleaning the MAF is pretty easy, too. Could a novice like me reasonably be able to perform both of these DIY? Thanks in advance!

 

If you have wrenches and a little patience, a can of throttle body cleaner and a can of MAF cleaner, you can do it. The hard part is gaining access to the parts you need to clean. The actual cleaning is almost as easy as spraying from the can. The throttle body can take some "polishing" but you don't want to touch the MAF at all.

So, if you follow the directions from this site, you can do it...but it appears you can wait another 50k miles with no worries. Might as well change out the air filter while you've got the pieces apart.