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 throttle body problem

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yong88
post Sep 10 2010, 06:10 PM

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QUOTE(skyther @ Aug 19 2010, 01:21 AM)
Allright, I'm not a mechanic by trade, but I've worked on cars enough to know that some of the solutions offered here will do your car more harm than good.

That "FICD" posted above is a Vacuum Switched Valve (VSV) that opens up whenever +12V is applied to it. VSVs are used for EVAP and EGR control, *NOT* for idle control. All it does in this instance create an air bypass from your intake straight into the manifold. Wiring it up to your A/C compressor will cause your idle to go up to 1.5k - 2k RPM. There is no form of idle "control" here. In EFI engines, this will kill your fuel consumption and cause other issues like your car jerking/surging forward when you release your brake pedal, or even cause shifting issues if you have an auto transmission. This is because your ECU is no longer able to properly control the idle and will think you have a vacuum leak.I know some people are going to flame me for this, saying there are no issues with this setup, but trust me, this would cost manufacturers at most $5 to implement, and if it were this simple they would. Car manufacturers know more than you about their own engines. This "FICD" is not intended to supplement or replace your engine's idle control method. If your car wasn't designed with one, you shouldn't be using it.

user posted image

^ This is the device that Toyota uses to control idle. It's called an Idle Air Control (IAC) valve. It contains a stepper motor that is controlled by the ECU to vary the amount of air going into the engine to control idle. If you turn your A/C on, your ECU tells the IAC to open a little more to increase idle to compensate. Newer cars that have drive-by-wire/electronic throttle control may not have this as the ECU controls the idle by directly adjusting the throttle valve. This is also partially the reason why certain D-B-W cars accelerate very suddenly with slight movement of the throttle pedal - because the throttle butterfly is already partially open.

If you have an idle problem, fix the cause at the source.
Fluctuating idle can be caused by a plethora of problems from a dirty throttle body/IAC to electrical issues. I have a feeling you may have electrical issues on yours.

Most cars, when first started up, will idle slightly higher than normal for several minutes to warm the engine up. This is needed mainly to lower emissions, but also because every modern engine is designed with an optimum operating temperature range. Catalytic converters also require warming up to work efficiently, as does your engine oil as it's viscosity lowers as it warms up.

If your idle keeps fluctuating, you could have a faulty coolant temperature sensor. I would also check the AFM/MAF/MAP (whatever you have on your car - all does the same job, measure air volume) and the oxygen sensor (on your exhaust manifold/header pipe) in case one of them is causing your car to run in open loop. It can also be something as simple as a dirty throttle body to something nasty like a faulty ECU. I'd get the car checked by a mechanic who knows what he's doing.
For the love of God, do NOT seal your throttle body with silicone/RTV/FIPG, they are to be used as gaskets in oil pans and valve covers where hot oil is an issue, NOT throttle bodies. It is a b*tch to remove; your mechanic will hate you and will scratch the hell out of your throttle body trying to clean it all off.

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Throttle bodies / IACs / intake pipes will get dirty, this is normal. Your engine burns fuel, and carbon is a by product. This is also why your oil goes black, it's normal. Throttle bodies and IACs *should* be cleaned regularly, though most mechanics will not look at it until there is an issue with the car. It can be time consuming as to clean it properly requires removal of the TB, intake hose, disconnecting all the cables and hoses, etc etc. Some TBs also have coolant bypasses in them, and you need to top up the coolant after reinstalling the TB.

If your issue is caused by a dirty TB/IAC, clean it. Do not install the "FICD". If you're feeling poor, do it yourself. All you need is carby cleaner, a socket and ratchet set, a few old rags/t-shirts and patience. Alternatively if you're lazy, buy yourself a bottle of Seafoam and run it through a vacuum hose.
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..the symptom stated by ur posted i kena all..when release throttle pedal..car feel jerk a while..but installed a FICD is the only way to solve my idling problem..coz my ISC is melted..the only way is change throttle body? btw..i am driving an iswara convert to injeksen and i did not connected the ISC socket and use FICD.
yong88
post Jan 17 2011, 10:41 PM

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i will suggest u to repair ur throttle body or rather change a new one but not with FICD..
FICD cannot use with ISC..ue idling will become unstable...

 

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