After spending the past three or four weekends under the hood of my car trying to figure out why it is idling rough and burning too much gas, I am considering taking it somewhere. I've posted on here about this problem, and so far have had no success in tracking down the problem. I've replaced all spark plugs, ignition coils, fuel filter, air filter, cleaned the TB, and changed to synthetic. I've ohmed out sensors and looked for vaacum leaks. Either it is related to the hacked air box (which it shouldn't be because it didn't act up for the first 2 months of having it) or the synthetic change. I dont know. I'm not about to start replacing $150 sensors on a hunch. But on the other hand, I can't let it run ****ty like this without incurring cumulative damages. Maybe someone can help me out here, because at this point, I'm frustrated with it. Also, if I HAVE to take it somewhere, where would you guys recommend? I live in the Tampa/Clearwater area and would consider taking it either to a large chain type shop or local upon good rec. (Wish I could copy this thread into the regional as well) It just seems like there is so much complex **** with the max, and I'd hate to take it to someone who knows basically what I know or less. Please help me out here.

 

So your saying your not pulling a single code

 

It could be a leaky injector.

Did you ohm out or listen for each injector to fire?

What plugs did you use?

 

I see you have 2 problems on the post. One is the rough Idle and the other is the problem with burning too much gas. I don't know if you have posted your problems before but to help you with your problems.....

1. What is your idle?
2. How much gas are you burning? (miles per tank, or mpg if you can)

 

Strangely, not pulling any codes. I haven't checked the injectors, being that the car only has 40K (mostly senior citizen driven).
Plugs- I switched from the factory ngk laser platinums to ngk iridium which are supposed to be just as good if not better. I checked gap, etc...

Idle- It is going high, when car is started up to 1500 and then slowly goes back down to 650ish after 5 or 10 minutes. Prior to a few weeks ago, the car never ever did this. Always idled perfect.

Also, in terms of gas mileage, it is getting about 15 to 16 as opposed to the normal 22 I pull around town (estimated from fillup cycles).

 

The idle behavior (high at cold start, slowly settling at 650 when the engine is fully warm), is how it is supposed to work ... is this what you mean by "rough idle"...

The MPG looks suspect... have you tried checking for codes (even though the CEL is not lit).. a bad KS will cause a severe MPG drop and will not set the CEL.

 

sounds like a MAF problem...maby going bad or the connection being loose..
that fixed mine right up..

 

I thought about that - but most MAF failures I've seen/read about cause stalling/hesitation... the OP doesn't mention either of those symptoms.

However - it would definitely be worthwhile checking the MAF.

 

I thought about the MAF, checked connection and such. I can't afford to just replace it without knowing that is the problem.

No, I don't mean that by "rough idle." I mean rough idle by rough idle. Like when you are holding the steering wheel and you feel the car jump and shake when it never has before.

As far as idle speed, my car had always started up and gone right to 650RPM whether it was cold or hot. Idled like a brand new car and drove the same. Now it takes 10 or so minutes, plus idles rough, I don't think so.

 

Check your ECU for codes it could be a bad KS they cause bad gas mileage

The idling is totally normal when the car is cold and it like under 50 outside

 

and to clarify with that last post...

the temp is not near 50 (FL) and the car never ever ever ever idled rough before. You couldn't even feel the car idle before because it was so smooth.

 

ok...

1) A bad KS will not cause a bad idle, bad mileage yes, your timing gets retarded and into safe mode.
2) MAF is a possibility
3) ECT is also a possibility, if its going bad or reading incorrectly it can make you run rich, running extremely rich will ruin your idle.
4) Leaky Injector is also a possibility in this case..

How does the car run on the street? power loss? ever turn off on you?

 

Just go outside now and check your codes im sure it the KS

Seems like you just want to post because like 4 people mentioned it could be the KS but you seem to have no interest into seeing if that it. It takes 1 min to check to see

 

10 char.

 

what about a coil pack you did just change the spark plugs could you have damaged one of those by accident? a coil pack would make it miss(rough idle) and it would make it use more gas (running on <6 cyl.). makes you push alittle hard to go the same speed.

 

I agree with the 81 years old dude.

Looking at your post, you have done and replaced everything except for the 2 major things that MIGHT cause your rough idle (MAF) and bad gas mileage (KS).

Check to see if you have any codes even though you don't have CEL on.

Have you done any upgrades before this problem? or some kind of tuning?

 

If you go back and read the first post in the tread, I tell exactly what I did to the car. This includes replacing ALL of the coils and lists any mods/changes I've made. I don't know how to check for codes without the engine light. I'm sure it is something to the effect of looking under the front/middle console to check the ECM/PCM. However, I did ohm out sensors underhood to try and narrow down the problem.

 

Just pull the codes using the regular ECU screw method (see the ECU sticky). If the KS code is set (Even tho the light is off), you will get 0304 instead of 0505.

 

The ECU is located behind the center console on the drivers side. It is accessible by removing the plastic cover panel right next to the gas pedal. The ECU is a metal box with a screw on the side covered by a piece of tape. Peal back the tape to get at the screw. With the ignition in the “On” position, turn the screw all the way clockwise, hold for at least 2 seconds, turn it all the way counterclockwise. Your CEL will now start flashing out any codes stored in the ECU. The codes are two digit numbers. The first number is signaled by long flashes, there will be a two second pause, and the second number will be indicated by a series of short flashes. Long-long-long-pause-short-short-short-short = 0304 (KS fault). There may be more than 1 code in the ECU, they will be flashed out sequentially and the whole sequence will repeat. To clear the codes from the ECU, follow this sequence: clockwise, hold, counterclockwise, hold, clockwise, hold, counterclockwise.

A good KS will measure ~550 k-Ohm resistance between the left pin of the KS and ground. You can check the resistance without removing the KS by following the harness to the connector. The connector has two pins, only one of them hooks up to the KS, so try them both. The act of whacking on the KS with your wrench can (temporarily) start it working again, so checking the KS once you removed it may not give you the bad reading you suspect. Hint: the connector is not the green one closest to the KS that gets in the way of sticking your hand into the engine cavity (1995-1996 models – most likely 1995-1999). The correct connector is a few inches closer to the front of the car. A heat shielded wire leads into the bottom of it and there are two wires coming out the top, one clear and one black.

 

Way to cut and paste

 

Thanks for the last post (i.e. cut'n'paste), very informative on ks info.

What I'm not understanding at this point is why I should have to manually pull the trouble code if there is an already existing issue. Shouldn't it already flash a code?

 

The KS code (if thats the only fault) won't turn on the CEL. Ask Nissan why... but the code 0304 will be returned if you check for codes (if the KS is bad, even if the light is off).

 

It's called a 'ghost code'

 

Just pull the damn code and come back with the results.

 

interesting, so nissan has some sort of partnership with the manufacturer of the ks. lol "ghost code"

I'm going to do it first thing in the morning, both my ryobi 18v's are dead and need charging.I'll post results. I appreciate all of the good input thus far.

So, at this point, it would seem to be the ks, MAF, or ECT given the symptoms? What about oil temp sensor?

 

Oil temp sensor? Someone enlighten me.

 

I think you mean ECTS (engine coolant temp sensor)... and why do you need an 18V power tool battery to pull codes? (perhaps for a flashlight?)

Don't rule out injectors... just cos' they only have 40k on them, doesn't mean they can't fail.

 

It's what McD use to make sure the oil is ready for the fries you just ordered Have a good weekend

 

as apparent in the post a few previous to this, i know clearly what the ECTS is. I need the 18v so I can connect it to my flashlight. I'm not about to go playin around in my car without it. I won't rule the injectors out, but will say that i'd scoff at the idea of this type of problem happening in a Honda with the same type of mileage. Damn I miss them. And how much are the 3.5Ls? Thanks for the info, ill get back tomorrow. I'm out-

 

that was freaking easy. first code 0102 - MAF. Strange, this came after spraying TB cleaner directly into TB during partial throttle with MAF removed. Blew out black smoke, let idle for a few and turned off. Reinstall MAF + rest of intake and start up to notice check engine light. Think this was just a temporary result since the only codes present since resetting are 0505 - in the clear. Car idling better and responding better as well. Did that, dropped on some new rotors, and gutted the cat. BTW, gutting it caused no difference in exh note, though a slight power gain at midrange noticeable.

 

I had somewhat of the same problem. Did you try cleaning your IAC valve? I did that and mines works fine now.

 

nah, I looked at doing it, but it seems like a real pain in the ***. Besides, I need better pics of exactly how to do it since everything ive found shows weak links and zoomed out pics. I might try it if I knew how. But apparently cleaning the tb not only by scrubbing/wiping but spraying plus resetting did the trick somewhat. Drop me a good link on how to properly do the iac and ill give it a whirl.

 

I didn't take pictures, but it's easy.

1) Unplug the 4(?) electrical connectors
2) unbolt the connector bracket from the IAC with a 10mm
3) Unbolt the 3 bolts holding the IAC from the intake.
4) Remove the screws and use carb cleaner or brake cleaner and a wire brush to remove any buildup. Remove each solenoid and make sure the plunger end is clean and so is the orifice it plugs.
5) Replace and reinstall.