My 91 240 SX DOHC (127K miles, bone stock) is idling very rough. Originally it started dying at every stop and the engine light came on. It was only putting out a code 45. Also I performed the 02 sensor ECM test and after the 2 minute warmup at 2000rpm, the light nearly stopped blinking to indicate that the 02 sensor was defective.
Since then, I have replaced the 02 sensor, cleaned the intake near the throttle valve, removed and carefully cleaned the IAA valve assembly.(By the way I know that the FICD valve works fine when AC is turned on). First cleaned, then eventually plugged and disabled the AIV valve and assembly, cleaned most electrical contacts, checked for vacuum leaks. EGR appears to be working. MAF is measuring .5 V with key on, 1.3V at idle, and about 2.7 at higher idle. The injectors all read 11 ohms, and there is no visual sign of leaking. I did notice that the hose coming from the PCV valve and back is a little sooty.
Currently the engine light is not coming on but the darn thing still idles rough and sometimes smooths out, only to get rough again.My temp sensor measures 1.6K ohms at 70 degrees, and 300 ohms at about 170 degrees.
One question I have is about the air bypass regulator. When they talk about pinching a hose, is it the one (about 1" dia. that goes up front and connects to the main air input plastic duct. I have pulled that hose and noticed that the air is always flowing in to the regulator - even with engine hot. Is the air valve defective? Also if I plug it when hot the engine won't run, hmm?
Another question is about the throttle position switch. It has 3 terminals. At closed throttle 2 of them are contacted together. At open throttle the other one and the middle on are contacted together. However, with the engine running and the cable plugged in, the center connector measures 12 V. Didn't I see somewhere that it should read about 4V ?
I am getting stumped on this one. Any suggestions would be greatly appreciated. Could my ECM be shot?
91 240SX Idles bad, Have Questions...
-
stillmatic
- Posts: 438
- Joined: Sun Aug 10, 2003 12:33 pm
My brother's 91 240sx used to have the same idle problem on a complete stop. His car would die unless if you tap the gas a little bit. He decided to get rid of the car because he didn't want to deal with it anymore. So I took over his car for free and immediately replaced the battery. The car has been rock solid ever since and not once has the engine died on me.
since the throttle switch is just that, a switch 12 volts could be acceptable. usually sweep sensors are 5v refrence. when you pinch off that hose the car should die when it is at operating temp due to it is the primary source of air into the intake since the throttle plate is closed. Try shootin some brake clean around the intake gasket,egr base, and any where else a substantial vaccum leak could occur. If your idle steadies out for a sec. you got a vaccum leak. you could also moniter the effects of spraying carb clean or brake clean by monitoring the o2 with a volt meter. If the voltage spikes to .8 to 1v from 0v you hit the area where the leak is present. Good luck to ya