89 hatch rough idle and rough running

[kingmoochr]

Ive got a strange problem that i have not been able to solve with simple tuneup measures. from 0-3k rpm, my car has a tendency to run rough under decel. and partial throttle. its smooth under WOT and over 3k, and its not a consistent amount of jittering/misfiring/roughness. It also is much more pronounced after the car has warmed up. My other problem, which i believe to be related, is a sporratic idle. It will jump to 1500 occasionally, and when settles, never settles in the same place twice. it will settle at anywhere from 500-900 when its not jumping around. I can also actively hear the throttle increase and decrease in sound level even while the tach reads the same rpm, as if the motor is forced to try to actively maintain that rpm. Ive changes plugs, wires, air filter, oil, and had a lube shop perform a "fuel system cleaning". Still no dice. Im getting no codes from the ECU and no dash lights. However, i still believe it might be a management problem, some sensor possibly. Im not too farmiliar with 240s and their quirks (this is my first), so im not sure where to begin searching. Help would be much appreciated.

[Biggamehit]

all of the sensors are important, but some of the most important ones are in the MAF and also right below the lip of the throttle body. make sure that are in the other sensor is below that one by the lower radiator hose that goes into the engines block. on of the two of them has something to do with ur idle. make sure ur car is properly grounded also. a bad ground could cause ur car to idle funny becuase the plugs will not spark properly at all.

[MakotoS13]

my car was doin that and after checkin some stuff i just took it for a good hard drive for like 15 minutes.

idles perfectly now. sometimes ya just gotta stretch her legs.

[kingmoochr]

the car has been plenty streched, that isnt the problem. the issue is a genuine one, however, it isnt ALWAYS present. i will check the sensors and perhaps add another ground with the spare 4 gauge wire ive got to see if that helps anything

[ticklemeermuel]

hmmm sounds like it could be some kind of vaccuum issue. check a number of things, like make sure the maf is clean and that the wiring harness is cool. some wires might have been cracked. on my bro's p10 the maf had to be grounded and he had the same exact issues. on my car it was a boost leak but it did the same thing. another thing is there's a hose i think its about 5/8 that goes from the under the TB to the plastic intake thingy...make sure thats not cracked or disconneted or anything. let me know how it goes.

[ledzeppelin240]

Hah, Intermittent problem. I have the same problem with my KA24E. Check your grounds with an OHM meter. Then you could go into checking the sensors for correct voltage. I found out that my TPS was out and that has helped a bit. I replaced the coolant sensor and O2 sensor, spark plugs, wires, cap and rotor and it still doesn't want to idle. It is a very annoying problem. But just go through everything like I am or take it to a shop if you don't have the tools.

[Biggamehit]

yea i never checked my vaccums but its good to do so also like one of the guys said befor the 02 sensor could mess u up

[180sxdrifter]

i think u should check ur fuel injectors, and distributor....if its rough idle

[idlafie]

Ive got a strange problem that i have not been able to solve with simple tuneup measures. from 0-3k rpm, my car has a tendency to run rough under decel. and partial throttle. its smooth under WOT and over 3k, and its not a consistent amount of jittering/misfiring/roughness. It also is much more pronounced after the car has warmed up. My other problem, which i believe to be related, is a sporratic idle. It will jump to 1500 occasionally, and when settles, never settles in the same place twice. it will settle at anywhere from 500-900 when its not jumping around. I can also actively hear the throttle increase and decrease in sound level even while the tach reads the same rpm, as if the motor is forced to try to actively maintain that rpm. Ive changes plugs, wires, air filter, oil, and had a lube shop perform a "fuel system cleaning". Still no dice. Im getting no codes from the ECU and no dash lights. However, i still believe it might be a management problem, some sensor possibly. Im not too farmiliar with 240s and their quirks (this is my first), so im not sure where to begin searching. Help would be much appreciated.

Try a simple test...pull your spark plugs wires one at a time & see if there is any change in idle. If there are no changes in idle, then it could be a stuck valve or a bad spark plug wire. If there are change in idle, then it might be an idle adjustment problem OR a bad IAV valve. It's the valve that regulates air into the intake manifold, located on the back of the engine on the passenger side. There's supposed to be a reed inside of it. That can sometimes go bad.
http://www.240sx.org/faq/articles/servicing_the_aiv.htm
Anyhow, hope this helps..
ID