Hello everyone. I have a 1998 Infiniti I30 and for the past several weeks I have been chasing an ellusive problem I can not solve. My car feels like it is sluggish and gets bad gas milage, it also has a rough idle sometimes. I have changed the spark plugs, fuel filter, air filter, and cleaned the throttle body to no avail. I get about 19mpg on combined city and highway driving. I have no check engine light on, so thats why im leaning towards a bad coil and not a bad knock sensor. Does anyone have any opinions that might help?

 

Have your tried pulling ECU error codes? It will store codes without displaying a light right away...

 

How do I pull an ecu error code, I have hooked it up to a scan tool and never picked anything up before.

 

There is a black panel next to your accelerator pedal. Pull the black panel off. You will find the ECU. If you look closely there is a screw with some tape over it. Turn your car to ACC and get a flathead screw driver. Now break through the tape and turn the screw clockwise. You will hit a stop. Keep the screw there for 2 seconds then turn it all the way counter clockwise. Now go look at your check engine light. Count the number of short and long pulses.

These links will help you.
http://vbxmaxima.8m.com/ecu.html
http://vbxmaxima.8m.com/ecudecoder.html

 

A bad KS will not effect your idle. I think it's safe to take that device out of your trouble shooting.

What kind of spark plugs are you using?

A rough idle can be caused by either poor fuel delivery or weak spark.

 

I have the same symptoms but normal gas mileage and no codes? I'm thinking it's a coil. I was planning to test them using instructions in the Hayne's manual. Any suggestions welcome.

 

Ah well sounds like you are having similar prbs as me then. One thing I have no is that the bad or bad coils go out every once in a while and the thing runs on 5 cyl sometimes 4 for all I know. I know its not the knock sensor though that much is for sure. I'm gonna just replace all six coils at once. Doing the ohm test is a waste of time if you have coming and going prbs cause it always seems to clear up when I go to test the coils

 

I have multiple misfire in my 1998 Infinity I30 , I've changed the plugs and coils I also have a bad shake with backfiring and slow gear shifting