The car that I worked on was a 1998 240sx, manual transmission with only a sports package, no luxuary items added. The modifications done so far have been the following:-battery was relocated to the trunk of the car-the engine fan has been removed-the A.C. unit was removed-a cold air intake system
The current idle is 1000RPM once the car has warmed up, however when the car is first started and it's a cold start, it idles fine at 750RPM. The car has also been running rich, and the gas mileage has been horrible. I've tried looking on other forums to fix this problem before even attempting to bother you guys with this problem, however the only information out there is on early model 240s, nothing on a 98 model. I've also tried locating the idle adjustment screw, but have come up with nothing. I'm not sure if that is the problem, but I'm willing to try anything to fix this problem. Other than that the car is fine. Anyone that can help with this I thank you in advance, and the help is greatly appreciated.
Idle at 1000 after warm up
when first starting the car cold it should idle around 1200 to 1500 rpms. once warmed up when in computer control it should idle around 800 rpm base is 700+/- 50 . the higher idle once warmed up could be a vaccum leak so check all your hoses real good. also check intake manifold gasket by spraying carb clean or brake cleaner near where it meets the head once its warmed up. if you hear a substantial idle variation you have located a vaccum leak. pinpoint the area by spraying again and again til its to the point as soon as you srpay it changes idle. if thats not it then go for the idle adjustment. it is located through the # 3 and 4 intake runners near the back large screw should be obvious when you look down in there. but when setting this you need to put it in base idle mode.
1 Warm the car up to operating temp then shut it down.2 Disconnect the TPS and restart the car3 Rev it to above 2000 RPM 3 or 4 times then allow it to idle4 Adjust the screw to aquire 700 RPM +/- 50 5 Check timing set to spec on under hood label. 20BTDC???6 Shut car off and reconnect TPS7 Restart vehicle rev 3 or 4 times and allow to idle
after doing this the idle could be between 700 and 850 rpm depending on what the computer is seeing. Now since you have removed the A/C if your heater is in any defrost position the idle will bump up since the ecm thinks there is a compressor in the car. It rasies the idle to compensate for the load of the compressor. In defrost postion the Compressor is turned on to dehumidify the air in the car.This is done to help the defrost process.
1 Warm the car up to operating temp then shut it down.2 Disconnect the TPS and restart the car3 Rev it to above 2000 RPM 3 or 4 times then allow it to idle4 Adjust the screw to aquire 700 RPM +/- 50 5 Check timing set to spec on under hood label. 20BTDC???6 Shut car off and reconnect TPS7 Restart vehicle rev 3 or 4 times and allow to idle
after doing this the idle could be between 700 and 850 rpm depending on what the computer is seeing. Now since you have removed the A/C if your heater is in any defrost position the idle will bump up since the ecm thinks there is a compressor in the car. It rasies the idle to compensate for the load of the compressor. In defrost postion the Compressor is turned on to dehumidify the air in the car.This is done to help the defrost process.
ok FSM info here. it is near the rear from the side of the intake manifold it is on the idle air control valve it is a hole and inside you will see a flat blade screw driver slot. screw in to decrease idle, screw out to increase idle. spec is 650 +/- 50 not 700 as mentioned before. when all done and plugged back in idle should set around 700 rpms.