My 1998 Nissan Pathfinder 3.3 liter 4x4 automatic transmission makes a terrible shaking motion and loses power while the rpms jump randomly up and down. It acts like it’s not getting the right mixture of fuel to air.
The check engine sensor says it is my knock sensor and MAF sensor. I’ve replaced the fuel pump, fuel filter and MAF sensor about a month and a half ago and this fixed it for about a month. At my wits end and am afraid it’s going to leave me stranded on the road soon. Please help.
Have you been subjecting the vehicle to a lot of dust, smog or something like that? If so, it might be that your MAF sensor connections need cleaning. You can buy an MAF sensor cleaner online, just Google MAF sensor cleaner. Even though you have recently replaced the sensor, there is the engine part of the connections to consider. The electrical connections are what you want to clean, as the part is just not going to work reliably if any part of the two connections are dirty. This is most likely your problem since you recently replaced the sensor and had a temporary improvement.
It is also possible the replacement simply was of poor quality or even used (if you had the sensor replaced by a mechanic).
Clean the contacts with the appropriate cleaner, and if that does not solve the problem, replace the part with the Nissan product.
If you paid to have this done the first time, you should be aware that it is a very easy part to replace (and to clean). It is mounted on your air filter housing and requires you to remove two screws and unplug and replace it. The part itself should cost a little more than a hundred dollars. I guess the Nissan part might cost you as much as twice that.
As far as the knock sensor code goes, the failure of this part will often set off your knock sensor code, as the symptoms include knocking. You don’t need to replace this sensor as it is only reporting a symptom.
I just bought a 2000 Pathfinder (same engine as yours) and replaced the knock sensor in order to pass emissions. The rough idle at start up cleared. The CEL codes for oxygen sensors went away. And the truck generally drove better and had more power. I could be wrong, but I think the knock sensor is to detect pinging, or pre-detonation, in the engine. But really, it affects the computer by giving it erroneous info when it isn’t working. The computer sees oxygen numbers on the front side through the MAF sensor and from the oxygen sensors at the exit through the exhaust. I think the knock sensor could help if it is replaced. Shop that did it for me charged $600 including labor because it is difficult to replace it, it requires removing the intake manifold.