Car wont idle right NEED HELP!

[aznfab213]

A few days ago my car started to idle weird sometime when I am at the light the idle will drop from around 900 to 200 then come back up. Then I got a check engine light. After diagnosing the code, I found that the Knock sensor was bad. I just replaced the knock sensor today and reset the ecu, but it is still idling really weird. Does anyone have any idea what it could be? By the way, my car is a 91 240sx with ka24de. Thank you for your time.

[JDGrimReaper666]

I got the same problem. Tried messing with the throttle cable but my revs won't stay stable. Maybe you have the same set up.... Mine is a 93 s13 5 speed with a auto ecu. Itll idle at 600, then go up to about 1400 and drop again. It will do that continuously. Sometimes itll drop down to 500 and stall. I know auto ecu's do idle drops but theyre not suppose to go back up, ive ran this ecu for over a year with no problems until now.

[aznfab213]

I got the same problem. Tried messing with the throttle cable but my revs won't stay stable. Maybe you have the same set up.... Mine is a 93 s13 5 speed with a auto ecu. Itll idle at 600, then go up to about 1400 and drop again. It will do that continuously. Sometimes itll drop down to 500 and stall. I know auto ecu's do idle drops but theyre not suppose to go back up, ive ran this ecu for over a year with no problems until now.My setup: 91 240sx coupe auto-> 5 speed manual conversion with an auto ecu. idles at around 900 then sometimes will go down to 200 then back to 900 sometimes it just jumps up and down. It only started happening recently.

[aznfab213]

does anyone have any ideas what it could be?

[Ace]

I had the same issue with my last car. Auto to 5 speed swap with the auto ECU. It could be something in the programming but beyond that I don't have a solid answer. Seems to be pretty common with auto to manual swaps though. Never had it happen with a 240 that came stock with a 5 speed trans.

[s73]

I had similar issues with my s13, not sure its the same issue you were having. My car's idle would bounce around like that at first, then it gets worst and worst.....then it would just stall out. It got so bad that its not even drive-able.....every time when i press the clutch to shift the car would die!!

this is what i did (not sure if everything i did was necessary or has to deal with my problem, but at the end it fixed it)

1) Check all vacuum lines for leaks, cracks, etc
(i replaced one with a small crack)

2) Clean MAF
(make sure you go to the auto parts store to get the right cleaner)

3) Check EGR
(my was ok)

4) CLEAN IACV
(this was prob the one that fixed it, its not hard but kinda hard to get to, i have big dumb fingers and if i can do it, pretty much anybody can do it. Just have to take it out, take it apart, and clean it with some carb cleaner, put it back together, and put it back on...and of course new gasket if yours got all messed up, my was looking ok so i just slap on some gasket adhesive and reinstall)

NOTE...i found a easy way later on that might be worth a try for you.....instead of taking the whole IACV out, just take out the idle adjusting screw and shoot some throttle body & air intake cleaner in it....then readjust idle....and you are done....

[aznfab213]

Today I checked the spark plugs to try to find the leaking injector. All of the sparkplugs looked dirty so I did a thorough clean and now it idles very smooth. Weird but it worked. If that is not truly the problem then I will take the recommendations presented to me above. Thanks guys for the help.