What is the RIGHT way to adjust idle speed on a 90 240sx?
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QuinGarcia
- Posts: 119
- Joined: Fri Oct 18, 2002 11:43 am
What is the RIGHT way to adjust idle speed on a 90 240sx?
The car runs good except the idle speed is up around 825 ever since I fixed a vacuum hose leading to the BPT valve. The idle was around 775 before I fixed this, now it's too high. I saw that on my ECU it says "idle speed adjustment". I tried turning that adjustment screw while the car was running but it had no impact. The idle might have changed speed for a second but it definitely remained at 825rpm. When I made this adjustment I did not remove the throttle sensor harness connector( the connector with the wires that come out of the top of the TPS that terminate in a weatherproof connector.) Since then I have tried adjusting the idle speed screw on the throttle body. I was nervous doing this as I saw some red paint on the adjustment screw and set screw denoting where it should be (I am not sure if this was a factory mark or a mark left by a mechanic). Before adjusting it this way I made sure to disconnect the throttle sensor harness connector(as mentioned above). After disconnecting, the speed remained at 825 but as I adjusted it (closing the throttle plate) the idle speed would drop down for a second, but then it seemed like the Idle Air Control would kick in and raise the idle speed back to 825. I have no idea where the idle screw on the throttle body should be now and I have no idea where the screw on the ECU should be now. And my idle is still higher than I want. Supposedly my idle should be around 750 according to the manual. How can I fix this?
700rpms +/- 50, the FSM says that, there's a scew on the IAA valve, that is how you should adjust it if the increments are small.
But if your is sitting at 1500, you have to do some more stuff,
Here's from the FSM:
1.) Before adjusting idle speed on the engine you must visually check the following items first: air cleaner for being clogged, hoses and ducts for leaks, EGR valve for proper operation, all electrical connectors, gaskets, and the throttle valve and throttle valve switch operation.
2.) Start the engine and warm the engine so it reaches normal operating temperature. The water temperature indicator should be in the middle of the gauge.
3.) Race the engine to 2k-3krpms, a few times under no load and then allow it to return to idle speed.
4.) Connect the tach. according to the instrument manufacturer's directions.
5.) Check the idle speed in the neutral position for both manual and autmatic transmission models. (700rpms for manual)
6.) If the idle speed needs adjusted, you must disconnect the throttle position sensor harness connector.
7.) Adjust idle speed to tune-up specifications(700rpms) by turning the idle adjusting screw. Which is located on the IAA valve block which is attatched to the back of the intake manifold, there's a screw there.
8.) Stop the engine. Connect the throttle sensor harness connector.
9.) Remove the Tach and road test for proper operation
If your car has a tach. you don't need to buy a clip on tach. Just use your in-dash tach.
But if your is sitting at 1500, you have to do some more stuff,
Here's from the FSM:
1.) Before adjusting idle speed on the engine you must visually check the following items first: air cleaner for being clogged, hoses and ducts for leaks, EGR valve for proper operation, all electrical connectors, gaskets, and the throttle valve and throttle valve switch operation.
2.) Start the engine and warm the engine so it reaches normal operating temperature. The water temperature indicator should be in the middle of the gauge.
3.) Race the engine to 2k-3krpms, a few times under no load and then allow it to return to idle speed.
4.) Connect the tach. according to the instrument manufacturer's directions.
5.) Check the idle speed in the neutral position for both manual and autmatic transmission models. (700rpms for manual)
6.) If the idle speed needs adjusted, you must disconnect the throttle position sensor harness connector.
7.) Adjust idle speed to tune-up specifications(700rpms) by turning the idle adjusting screw. Which is located on the IAA valve block which is attatched to the back of the intake manifold, there's a screw there.
8.) Stop the engine. Connect the throttle sensor harness connector.
9.) Remove the Tach and road test for proper operation
If your car has a tach. you don't need to buy a clip on tach. Just use your in-dash tach.
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QuinGarcia
- Posts: 119
- Joined: Fri Oct 18, 2002 11:43 am
thanx for the response. But, like a fool I first messed with the adjustment screw on the throttle body. And obviously It did me no good. Here's the bad part: the screw that i adjusted on the throttle body happens to be factory set and is not supposed to be messed with. I have a feeling that if that screw is off, then it might mess up some other systems. There are no markings on it to indicate where it should be set at. Do you know how to reset it to the proper position so the throttle blade is allowing the right amount of air in?