How to Clean the Throttle Body
1990-1994 Lexus LS400
Cleaning your throttle body may help solve a rough idle problem. Normal idle without the A/C on is 650 RPM, + or - 50 RPM. Cleaning should also gain back some lost horsepower. The hardest part about doing this is getting the throttle body off. You NEED to take it off entirely if you want to completely clean it. My throttle body had a carbon build up around 1-2mm thick! You can't get it completely clean unless you take the throttle body off.
Someone recently told me that throttle body cleaning helped get rid of a diagnostic code 71. If you get a check engine code 71 (EGR system malfunction) you may want to try this first since it doesn't cost much. After doing the cleaning, remember to reset your ECU by disconnecting the battery for a minute.
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1) If you want to be official you can drain some engine coolant; steps 1-4. I have found this step can be bypassed since the coolant hose that goes through the TB is one of the highest points in the cooling system. You may get a few coolant drips when you disconnect the bypass hose in step 9 but it can plugged with a cheap plastic pen.
2) Remove air intake and engine covers . Steps 3-10.
3) Disconnect the throttle position sensor.
4) Disconnect the 3 cables and then loosen the cruise control cable bolt.
5) Remove this hose so you have some room to work.
6) Disconnect these three vacuum hoses.
7) Undo the 4 12mm bolts that hold the throttle body on.
8) Disconnect this coolant hose here. This one was a real pain, it took forever!
9) Unclamp the other two hoses on the throttle body and then pull the throttle body off. This is where you'll have to do whatever works best for you. It's a really tight fit, which makes it hard to take off. I unclamped the big coolant by-pass hose first and then pulled the throttle body off. After that I disconnected the smaller coolant hose and then the throttle body was completely off.
Here's a look into my air intake chamber with the throttle body off.
Here's what the main side of the throttle body looked like closed, not so bad....
...however the side that faces the air intake chamber was horrible! There was about 1-2mm of carbon build up on it.
10) Clean the throttle body. I used STP throttle body and air intake cleaner. I started by spraying the cleaner on, letting it sit a while, and then wiping it off with a rag. There was just too much on there to do it that way, it needed to be scraped off with a screwdriver. Using a flat screwdriver I was able to get most of the carbon off fairly quickly. Once the bulk of it was off I used the cleaner and rags to finish it up.
11) Clean up the air intake chamber as much as you can. I scraped off as much as I could and then used the STP cleaner. When it was clean I replaced the throttle body gasket (part # 22271-50010) with a new one.
12) Connect the small coolant hose and then put the throttle body back on. Torque the 4 12mm bolts to 13 ft-lbs (185 kg-cm, 18 N-m). Finish connecting the other hoses.
13) Put everything back in reverse order of removal.
14) Follow steps 16-23 for filling the coolant, if you drained any.
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