Bad Knock/ MAF sensor codes (97 QX4)

[GoodOmens]

I recently replaced my spark plugs, wires, fuel filter and air filter on my 97 QX4 and have been receiving very bad idles that sometimes results in stall-outs or unusually low idles (200ish rpm).

When a shop was doing other work to my car they had told me my spark plugs were loose. While I have yet to check them (Will do so tomorrow morning) today while I was getting some anti-seize for my plugs I had Auto-zone check my computer. They came up with bad knock and MAF sensors. I noticed a light clicking sound when the car is a slow idle roll and also a rough engine sound at around 40~50 MPH.

Do you think re-tightening my spark plugs will fix the problems or could a bad MAF sensor be the ultimate cause? I installed a K&N filter so oil could possible have leaked onto the sensor?

The guy at autozone recommended unplugging the MAF and driving around to see if the problem is resolved (If it is then it is a problem with the MAF). Should I try doing this as well?

I know the knock sensor will be expensive to do as I don't really have a good place to do that sort of work.

Thanks!

[fueler]

the guy at autozone is a douche bag. Your truck will barely run if you unhook the MAF. K&N filter can gunk up the MAF in our nissans. Not "leak", like you said, but more like a vapor as the air is getting rushed through the intake pipe. Remove the MAF carefully and clean with electrical contacts cleaner, and watch how good the car runs. PS only use NGK or japanese plugs. I hope you didnt install Bosch or Autolite, or the such....

[GoodOmens]

They were cheap NGK single platinum tip plugs that came up in the computer at Auto Zone for the truck (Was there a specific type of NGK I am supposed to watch out for?)... I'll check the plugs to see if their is any type of strange fowling.

I'll get some MAF cleaner tomorrow and try from there. You think it could be a rotor cap issue?

The trucks got roughly 190k miles so a failing MAF would make some sense .... how long do they typically last?

Thanks for the response BTW ... right in line to what I've been reading to do

[fueler]

any NGK is good i predict MAF these VG33's are pretty solid, but i wouldnt be surprised if it was the rotor/cap or a failing spark plug wire at 190k.... but start with cleaning the MAF. Our VG33's typically run to 300k miles with just oil changes.

[GoodOmens]

Plug wires have 5k miles on them as do the plugs themselves.

As a update I did find a loose spark plug , but after tighting the plug and cleaning the MAF (With proper cleaning) I'm still running rich and stalling out. I took it back to Autozone and was getting the same errors from the ecu.

I did notice the plugs already had a light carbon coating as further proof the engine is running rich.

I bit the bullet and ordered a MAF ... hope it fixes it.

[GoodOmens]

Huh after replacing the MAF my engine is running fine but I'm still getting a knock sensor error.

Will this go away? I'm thinking of running a tank of 91 though to help burn some of the carbon build up. Maybe running sea-foam through?

[fueler]

i dont know anything about the knock sensor, but i seafoamed my VG33 at 120k, made A LOT of smoke, and seems to run better and healthier

[GoodOmens]

How did you put it in?

I know the can suggests a vacuum line but I don't know which one to do?

[GotDirt443]

yea i seafoam through the vacum line works great but i always spill tons of it... lol.. i love the stuff

[fueler]

How did you put it in?

I know the can suggests a vacuum line but I don't know which one to do?

any vacuum line thats easily accesible and connected to the intake manifold. I personally used the brake booster line. Ive used a first can of seafoam - half in the intake, quarter in a partially filled gas tank, quarter in the crank case (where the oil goes) After all is said and done (maybe 50-100 miles), you will want to change out the spark plugs and change the oil. Seafoam burns hot and can foul plugs, and your oil will be NASTY from all the crap you loosened up and burned off.

Personally, my favorite part of the seafoam is the smoke that comes out the tailpipe. I mean kids jumping off their bikes and covering their faces, people giving me the stink eye and some shouting, stares, meanwhile i'm just driving around with a huge smile on my face and a smokescreen behind me

[tmorgan4]

The knock sensor is really not something to worry about. It's known for going out, and doesn't appear to reduce power or milage in our vehicles even though some claim it does. It is a big job to replace it, since it sits in the valley of the VG33 under the intake manifolds. It will not throw an check engine light, but the code will come up if you scan for codes. It will not go away on its own.

Tons of info on it if you search around other forums.

[disel78]

From all the forums I have read about our cars and just in general, I would never put SeaFoam in my (OIL)......have read that it is just not good for seals or cars with alot of miles....and to drive on it with it in there SO BAD! Auto RX it and keep SeaFoam in the fuel systems.

[WhiteKnight]

What's AUTO RX?

[02pathy]

u didn't have to replace your maf sensor all u had to do was to clean it with air intake cleaner and reboot the computer unless u did the resistance test and the maf itself was bad as for the knock sensor try some octane booster and maybe a can of intake cleaner too, if the knock sensor can be cleaned clean it, the throttle body and valve and spay some inside the intake too after your car is hot, let it sit for 10 to 20 mins then turn on ur engine and holding throttle cable open slightly spray more cleaner in the intake maybe a can if u like then take if for a boot on the freeway, change you oil soon after

i know this tread is old but its good info