Hello, I'm a newbie here. Just bought my first Toyota ever, a 1985 pickup with 146K miles. The engine starts readily and pulls well. The idle is smooth, but that's the problem. The truck failed state inspection because the idle is too high. How does one adjust the idle? The engine has a two-barrel carburetor. I don't see any idle stop screw or idle mixture screws. All the vacuum hoses look good... no cracks, no breaks, nothing mysteriously disconnected or blocked off. Please advise.
You can find repair information for that model, including carburetor diagrams, at
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but
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and
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may also be of help. Factory or Mitchell manuals are much better than anything else, especially for fuel and emissions systems. Toyota specifies many carburetor settings in degrees, but if you need them in inches or millimeters, check a Chevy Nova manual or a Mitchell for the Nova. Also if you ever have to disassemble the carburetor, beware that most diagrams, including Toyota's own, have the
2 fuel-cut solonoids mixed up.
The idle speed screw is unusually long, about 2", and sticks up about
45 degrees and is made to be turned even without a screwdriver. There are probably 3 idle speeds: base, fast, and idle-up, the latter set by adjusting the throttle positioner dashpot (do not confuse with the choke pull-off or choke opener dashpots). Adjusting the throttle positioner may require removing some hoses and plugging one fitting. Next to its adjustment screw may be another one for the throttle position switch, and it's very sensitive and if set wrong may cause the vehicle to fail an emissions test since it tells the computer when to read the oxygen sensor.
Success! The idle mixture screw was hidden behind a factory-installed no-tamper plug. I drilled out the plug, turned the screw, and the idle is now much lower. Thanks to all who offered suggestions.
I'm glad it's running better, but did you really adjust the idle _mixture_ screw to set the idle _speed_? On the 1985 Toyota Corolla (same basic carb), you adjust the mixture screw for maximum RPM, the idle speed screw for 650 RPM, then retweak the mixture screw for max RPM and the idle speed screw for 650 RPM. Finally you lean the mixture for a 50 RPM drop, and then turn the speed screw for the correct idle speed.
Yes, but only because I cannot find an idle stop adjustment. I found mention of the hidden idle mixture screw in an old Chilton manual. Keep in mind that my objective is to pass the state inspection. Once that hurdle is cleared I can restore the idle mixture to its former setting.
Did you check the exploded diagrams of the carb at
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The following may be your carburetor (there are 3 shown for that model):
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It appears the mixture and speed adjustment screws are on the passenger side, or 90 degrees clockwise from the side with the float level sight glass.
Try not to use a Chilton manual, especially for fuel, emissions, and electronics systems. About the only decent manuals for those systems are the manufacturer's and Mitchell's.
You should restore the mixture screw to its original setting, unless that setting is wrong, because running too lean isn't good for your engine and can make it overheat or ping and consume more gas. For the
1985 Corolla version, with the engine fully warmed up and in neutral or park, adjust the idle speed screw for 700 RPM and turn the mixture screw for maximum RPM, then readjust the speed screw as needed to maintain 700 RPM. Turn the mixture adjustment slightly again to verify the engine is at maximum RPM, and again turn the speed screw as needed to maintain 700 RPM. Then lean out the mixture by turning the mixture screw clockwise until the engine drops to 650 RPM. Finally set the idle speed screw for correct idle, probably 650 RPM for manual transmission, 750 RPM for automatic.
Did you check the exploded diagrams of the carb at
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The following may be your carburetor (there are 3 shown for that model):
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It appears the mixture and speed adjustment screws are on the passenger side, or 90 degrees clockwise from the side with the float level sight glass.
Try not to use a Chilton manual, especially for fuel, emissions, and electronics systems. About the only decent manuals for those systems are the manufacturer's and Mitchell's.
You should restore the mixture screw to its original setting, unless that setting is wrong, because running too lean isn't good for your engine and can make it overheat or ping and consume more gas. For the
1985 Corolla version, with the engine fully warmed up and in neutral or park, adjust the idle speed screw for 700 RPM and turn the mixture screw for maximum RPM, then readjust the speed screw as needed to maintain 700 RPM. Turn the mixture adjustment slightly again to verify the engine is at maximum RPM, and again turn the speed screw as needed to maintain 700 RPM. Then lean out the mixture by turning the mixture screw clockwise until the engine drops to 650 RPM. Finally set the idle speed screw for correct idle, probably 650 RPM for manual transmission, 750 RPM for automatic.
I had no trouble accessing the AutoZone home page or doing parts lookups. However, I did not discover the way to find technical information such as the exploded view diagram. Your guidance would be appreciated.
I agree. Chilton is a last resort. I own the factory service manual for all my vehicles except this newly-acquired Toyota. I tried to buy a FSM for the Toyota on eBay but was out-bid. I'll try again.
Done. That raised the idle speed and also smoothed the idle. I'm happy with this higher idle speed.
Thank you for your interest and useful information.
I believe you have to register and log in. Then click on "Repair Info" and then "Vehicle Repair Guides," which will take you to a large list of vehicles. Choose yours, and you'll be taken to a page where you can select the area of interest for that vehicle (brakes, electrical, fuel system, etc.). Click on "fuel system" and then "carburetor." Scroll down to the diagrams and click to enlarge, which will open a new window. Right-click on the enlarged picture to save to disk.
I don't know if you're familiar with Toyota factory manuals, but they're unusually detailed, even compared to other factory manuals, with a separate illustration for almost each step of every repair procedure. But it seems that many of them have a misprint for the diagrams of the carburetor: The 2 fuel cut solonoids may be mixed up. One solonoid has 2 wires, the other just 1, and it is possible to install them backwards, so take note before removing the carb.
If the engine bogs down when you use the high beams or A/C, you may want to check the idle-up. You have to first disconnect the 2nd hose from the end on a thermostatic valve with 4 houses going to it and plug the nipple. Start the engine (turn off all accessories) and unplug the hose at the end of the throttle positioner dashpot (has 3 hoses; leave the 2 on the side alone) to make the dashpot press on the throttle. The adjustment screw is at the end of its pushrod and is facing the dashpot (the other screw is for the throttle position electrical switch and should be left alone; its adjustment is touchy and affects when the fuel system runs in closed loop mode). With the engine in neutral or park the idle-up should be around 800-900 RPM.
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