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Cleaning the Throttle Body

Also read Dan Thompson's comments on idle and cleaning of the Throttle body

Why clean it?

red_triangle.gif (202 bytes) Comments by Allen Chan

I talked to my mechanic friend about the trick of cleaning the throttle body for better engine performance. He gave me an education about this topic.

The throttle body gets dirty from the engine gas recirculation. There is a small hose that sends post combustion gases into the intake, I think for emission reason. This post combustion gas dirties the throttle body and the rest of the intake manifold. So when you clean only the throttle body, you solve only part of the problem. He said the old fashion carburetor cleaners also cleans the throttle body, and the rest of the deposits on the intake manifold.

So we pumped most of a can of gumout carb cleaner into the intake manifold. I also filled the tank with 89 octane gas. I was cheap so I always used the 87 octane gas. The combination of the two did wonders. The car got 200 miles for half a tank of 89 octane gas. Previously, I would get 160-ish mile on half a tank. I can't say how much either contributed to this drastic increase in mileage.

I did not lead foot the car much with this tank. I was interested in finding how thing effected the mileage. The next tankful, I will lead foot things.

Moral of the story: a bottle of gumout carb cleaner cost $2.00, and it might save you the work of removing and cleaning the throttle body. When you send the carb cleaner into the air intake, maker certain the little red straw is firmly attached. Mine shot into the intake. luckily, it was caught by throttle body.

How to do it.

red_triangle.gif (202 bytes) Procedure by Jim Wright

I found that after cleaning my throttle body, my idle speed was no longer adjusted properly. I'm not sure why that was, but you might want to check yours after doing this.

You will first need to remove the large hose going from the intake to the throttle body.  (The Intake is where your air filter is.) There will be a large clamp at each end of this hose, and another near the intake, these can be loosened with a Phillips screwdriver.  There is a vacuum hose near the throttle body that must be removed from the hose, and there are also two other hoses that need removing from this one.  Use a pliers to spread the clamps, and work the hoses loose.  Once the two end clamps are loosened and the other three hoses removed, remove this hose assembly.

You now have access to the throttle body.  Take a broom stick and use this to push the gas pedal to the floor, keeping the throttle wide open.  If you can find Throttle Body Cleaner, use this, but Carb cleaner can work too.  Just hold onto that little straw to keep it from flying into your engine!  Since the cans normally don't spray well upside down, I managed to lower the can down between some hoses and get it at a good spraying angle.  Soak the throttle body well, then use an old toothbrush to brush against any metal surface you can reach.  You'll find the brush will quickly turn black.  Spray in more cleaner, and keep brushing.  This may take a while.  Get as far in with the brush as you can, but again, be very careful not to let the brush drop into the engine!

When you're done, fire up the engine, and spray a final burst of cleaner into the throttle body.  Ignore the white smoke pouring out of your tailpipe, it will go away once you have the hose reattached to the throttle body.  Shut down the engine, reinstall the hose, and you're all set!

This procedure should probably be done once a year as part of your spring tune-up ritual.

Some additional Info about Throttle Body Cleaning

red_triangle.gif (202 bytes) Comments by Thomas Moxey

This is one area where the Nissan engineers fumbled the ball. The throttle body and intake manifold "collector" accumulates thick black oil residue over time due to the engine gas recirculation scheme employed on the SR20DE. To really do the job right you must completely remove the throttle body. This is a task as the cooling system is plumbed into the bottle of the unit and is difficult to disconnect and reconnect. Coolant will freely flow from the hoses upon removal and drain your system quite quickly. It's there to keep the temp high at the throttle plate in order to 'melt ' that sludge, DO NOT BYPASS THIS CIRCUIT. I spotted an article somewhere on the web where the author detailed the bypass procedure. If you do, be prepared to repeat this cleaning process quarterly!.. Also, there's a vacuum line attached to the bottom of the unit. Don't forget the throttle position sensor connector.

Now the fun begins. Take a flashlight and take a peek into the collector. If this is the first time doing this, you will see about 1/4" of tar lining the collector walls. Where did all that sludge come from?? The culprits are all those gas recirculation connections on the top of the collector (out of the PCV mounted in the valve cover belt side) and on the connection hose between the MAF and throttle body. On my '91 Classic the collector is below the actual horns to each cylinder, so dumping a pint or so of solvent just sits there. But on the later SE-R's they flipped the configuration of the intake (collector on top), so you can't just dump solvent in there as it would freely flow into your engine. Either way, this stuff has got to go, on the '91 the solvent was allowed to soak over night then mopped up with a shop towel balled up and ty-rapped to a flexible piece of 3/8" dowel rod. The throttle body was ultrasonically cleaned. The other way to do it is soak the throttle body in a mild solvent overnight. Pick up a new gasket (your Nissan dealer will have to order it, as they wouldn't wanna stock that pricey $4 item) Lube the ball joint before reattaching. Nissan would have you replace this item (rod), but it should last a few cycles.

NEVER, NEVER blow this junk through your running engine with carb cleaner. This crud has a viscosity of over 600 centistokes (much like roofing tar) and will stick like glue to anything it contacts, like the tops of your intake valves, solvent or not! This tar is very difficult to COMPLETELY burn off. So, a nasty 'cooking' effect occurs on the tops of your pistons as well (great if you want to raise the compression ratio;)) This stuff continues to burn all the way through the catalytic converter and will do damage there as well. The problem we face doing the 'in the fuel tank' type of additive cleaning is the risk of damage to the injectors, so the only safe way to do the job is to remove to TB and manually clean it.

As far as preventing this problem in the future, forget it unless you plan to race your car full-time. If you do you can eliminate ALL that pollution equipment and free-up about ten square feet of under-hood real estate. My car retains all but a couple pollution items, and still passes emissions tests.

Repeat this process yearly as part of your tune-up routine, a pain to do... but noticeably improved throttle response. I have begun the process of re-engineering the crankcase ventilation scheme employed on the SR20DE in order to eliminate this ugly job, I'll share this info at a later date.