Engine Running Rough
 

I recently bought a 2000 Maxima. The guy said it needed about $400.00 worth of work. When I brought it home and started it it would idle hi, then it would ramp up and down. I took it to VIP and they checked the codes. It showed a MAF and Air Control Valve errors. I changed the MAF and now the car idles rough and when I try to rev it it boggs down. It also sounds like it is missing. Almost acts like water in the gas. Any ideas? Would I still need to change the Air Control even though its not showing any codes? Or do I need to relearn?

1. Clear any ECM codes. You can do this by disconnecting the battery and stepping on the brake to discharge any remaining power in the system. Let it sit a couple hours and reconnect the battery.

2. Do the idle learn procedure. BUT, if you have any pending engine codes it won't work. The procedure is very specific about the parameters so follow them. If the idle learn procedure doesn't work and you still show the engine code for it you likely need a new IACV.

3. If you feel it is missing, but it is not showing codes then it could be a variety of things. Bad gas (use some fuel treatment), injector issues, spark plugs, ignition coils. Normally, what we have seen are bad ignition coils. Usually they do throw an engine code though.

Thanks for the response. After replacing the MAF I also installed a new battery as the old one was shot. My codes went away and it is still running rough. I don't have the Consult 2 but I found a post teaching how to do this procedure without it. I will post results. Thanks.

Before you do the idle re-learn, clean the throttle body/throttle plate. A lot of people get build-up and the idle suffers.

foodmany mentioned the IACV. The IACV has engine coolant flowing through it and also has a stepper motor built into it. The coolant has a nasty habit of leaking into the stepper motor and shorting out the windings. This in turn will cause integrated circuit chips in the ECU to burn up. Not good.

You can check the stepper motor windings with an ohmmeter. I think the proper reading is 28 ohms. The FSM has this all explained for where to test and the correct readings. I would suggest you check the IACV.

Enging running rough.
 

I took the stepper off yesterday to check it. I did not see any signs of coolant leakage. That seems to be working fine. I also cleaned out the plate. After doing the relearning it didn't change anything. The engine idles between 1200 and 900 but when it goes to 900 it runs like crap and sounds like it's skipping and sputtering.

Also wanted to say that when I bought the car it was showing codes for the MAF and IAVC. I have replaced the MAF and all of the codes are gone. Would a bad fuel filter cause these issues? The car was sitting for 6 months with almost no gas in it through the summer.

Well I changed my fuel filter at 172k and the original still looked good.. I doubt your fuel filter is the problem since those are usually good for the life of the vehicle in most cases.

engine running rough
 

Ok. Here is the latest. I checked all of my coil packs and got 1.4 on all of them. Next I decided to take off my IAC and see if it was dirty. Holy Crap was it sludgy. I am going to clean it tomorrow and put new gaskets in. My next question is inside the housing where the IAC mounts there is Venturi. That was sludged as well, but inside is very sludgy. Can I spray carb cleaner on the inside? Just not sure if that screw things up at all?

Ok sorry about being so ignorant. What I meant was where the throttle body mounts. The whole thing is gummed up really bad. I am assuming that this is what has been causing my bad idiling and bogging down.

depends how long the IVAC was shot but if you do some research here on the forum you will find that usually the IVAC burs the ECU chip that controls it... the only way to fix that is to replace the ECU or have someone who can fix circuit board replace the chip...

Bypass the throttle body coolant.
Did you replace the mafs with oem or junk aftermarket one?

engine running rough
 

Not sure if my IAC is shot. I replaced it with one I got at a local parts store. After replacing it all of my engine codes went away and currently not showing any it's just the engine is idiling a little high and when I give it throttle it boggs down.

My 2000 se had the same symptoms. Cleaned the EGR tube and everything is back to normal now. Search to find the procedure. Not a fun job but as soon as i took off my throttle body I could see the tube was completely blocked. How many miles do you have?

Is this safe to do? I'm going to do it as long as it doesn't throw any codes etc..

Yes

engine running rough
 

I have 159,000. I couldn't believe how much build up there was on the throttle body and IAC. Since I am not throwing any codes I am hoping that my ECU is ok. I will post results tomorrow assuming that I can get the gaskets tomorrow.

If you checked the ohms resistance on the IACV and didn't have any shorted windings, the ECU is ok. Secondly, you would probably be getting a P0505 check engine code if the IACV shorted. As far as I know, only a shorted IACV or shorted motor mounts will fry the ECU.

If coolant hasn't passed into the Motor area you're ok, that seems to be the suspected cause, the cooling passage and motor are separated by only an oring, if that oring fails, pop goes the motor, and if the motor goes, pop goes the ECU.

This is why you need to get the coolant OUT of the equation, now.

And disconnecting the motor mount is a good idea, I should do that to mine, never have.

FYI though: A 0505 code will NOT cause anything other than a difference at idle, may be a bit high, or just generally rougher, but it will not specifically cause a misfire, etc.

I am not showing any signs of coolant in the IAC. Also when I disconnect the brown connector my idle changes drastically. I had to order the gaskets through Nissan so hopefully tomorrow I can post results.

When i had problems with my MAFS, i replaced it with one from a local auto parts store, Lordco (vancouver canada). These ones which i actually didnt know were refurbished ones, i put the refurbished one in and it ran even worse! If i were you i would double check that MAFS. Find a known good used one or buy OEM.

Im just saying that cuz mine ran kinda rough and hiccuped through out the RPM range which led me to replacing it but, when i replaced it, it bogged, hesitated, missed just like u say.

I bought a new IAC and it will be here Friday. I will make sure to post results of the new IAC, Gaskets, and cleaning the throttle body. Hopefully this solves the issues I am having.

running rough
 

Ok. So I have gotten a tremendous amount of help and info on this forum for my problem. To date I have done the following,

Replaced the MAF
Replaced all spark plugs
Repalced the IAC
Replaced the coolant sensor
Took off and cleaned the throttle body
Put dry gas in
Done the idle relarn procedure more than once

And still my car idles rough, when I rev it up it doesnt go above 2500 and boggs down. It will sit idle around 1100 then drop to 900 but seems to skip. When I take it for a ride it won't let me floor it without dropping to 1000 and i loose all power. I can only keep it at 1100 and only for a short time before it drops all power. I can rev it up but it doesnt go it just revs up to 1200.

I am at a standstill with this thing and am looking for any help I can get.

Two things - 1. Did you remove the black throttle position sensor cover where the spring is? (I think that's what it's called. It's under the housing that the brown plug goes into on the throttlebody)

And 2. Congrats on the 66 :) I've got a 62 myself. Nothing is as good as old GMC iron. Nothing at all.

MAF is still bad LOL

I don't think there's anything else that can cause those problems. A super clogged fuel filter maybe (highly doubt the regulator is bad). But MAF is prime suspect b/c it wasn't OEM.

Agree with the above.

did you remove the throttle position sensor? if you did, make sure you installed it properly.

make sure your egr system is plugged and working properly, otherwise it might lock the ecu in limp mode. Usually that sets a code though.

has the car been sitting for long? sometimes the primary oxygen sensors go bad and cause a very rich condition and therefore cause a rough idling and driving condition without actually throwing a code.

one more thing, check and clean your engine grounds. I would add another ground engine to body to battery terminal. IT is very important for all electronics in the car to work properly to have good solid grounds.

GL.

engine running rough
 

While I really appreciate everyone help, I think I am ready to throw in the hat. I have done all that I can do without having a lift and other tools. I am going to take it to a garage tomorrow. I will make sure to post what the result is so anyone else having this issue might get help from it.

+2 on the MAF is still bad, wont rev over 2500rpm is a dead giveaway

Certainly sounds like a MAF problem as other members have pointed out, but it isn't necessarily the MAF.

I've had issues that matched the symptoms of a bad MAF and it turned out that the wiring was the problem. My MAF connector had exposed metal that were probably shorting each other out, which caused my problem. I just put some electrical tape around it to test my theory and that was the problem.

Extremely cheap and easy to fix, so if you haven't figured out the issue, you might want to check for that.

engine runs rough
 

I just wanted to update everyone. I just got a call from the garage. They put a used MAF on and the car purrs like a kitten. Thanks for the help. I only wished I had tried it before I sent it to the mechanic. Lesson learned. Now all I have to do is rotors, exhaust and inner tie rod.