Hey all,

First time on the forum. I already got some info to help fix my rear wiper, so thanks for that.

I wonder if anybody else has experienced, and I hope, solved this problem...?

My '98 QX4 3.3L (which has an old-style distributor with a single coil inside) starts great when cold (beyond -30 F) and runs great in general. About 5-6 months ago, it started running roughly just for the first two minutes of a hot restart. Typical scenario: Drive 20 minutes to the store; shut off engine; come out after 10 minutes; restart for the drive home. In cases like that, the engine starts immediately, but I need to sit in the parking lot idling for about 120 seconds before I feel the engine smooth out. If I start driving right away (or even just give it gas), my check engine light flashes and you can feel the engine misfiring. The codes are the somewhat vague misfire in cyl 2 (P0302) and sometimes the knock sensor (P0325). I have read that these two codes will appear whenever the engine misfires, for a number of reasons (i.e., the engine detects its own misfire, and the knock sensor senses the rough engine)--and don't necessarily give much help. Here is what I have replaced so far:

• Plugs
  Plug wires
  Ignition coil
  Ignition ignitor
  Distributor cap
  Distributor rotor

I have also run fuel injector cleaner through the system (Techron in the tank) a couple of times in different concentrations, with no change in the symptoms. The gas mileage seems to be somewhat worse than normal, but there is no cat overheating or symptoms of flooding.

A tech on another site mentioned the evaporative emissions system as being a known issue on the pathfinder from this era:

...this is caused by a vacuum leak, a vapor lock issue. this should be flagged as I believe all 1996 and 1997 possible 1998 pathfinders are going to have this problem. a P0302 #2 cylinder misfire w/secondary code of P0325 knock sensor. before replacing injector 2, wires , plugs, etc.. check the vacuum line above rear drivers side tire, small hose from charcoal canister up over the shock to the purge valve.The rubber hose from the canister connects to a metal hose then the metal hose connects back to a rubber hose to the purge valve. The METAL hose corrodes and leaks causing a #2 misfire for a small amount of time when warm started. pass this on few mechanics know of this. you will see the metal corroded.

I have checked the tubing mentioned, and also clamped off, one at a time, each of the vacuum lines under the hood that seem to run to the EGR, EGR control solenoid, and from the evap system in the back of the car into the intake system. None of these changed anything. Also, now that the weather is warmer and I'm driving longer distances, I notice that the misfire condition now comes during regular driving, after the engine is fully warm, and only for a short time span before it clears and runs smoothly again. Again, it is just like clockwork...start the hot engine, let it idle, feel the minor vibration as it misfires, and then feel it smooth out.

Does anyone know what the actual algorithm is in the engine management computer, regarding the evap and EGR systems? The above post would imply that the computer says: if engine is fully warm, open vacuum from A to B for 120 seconds after hot startup and then again ever 10 minutes, or something like that. If so, that matches my experience with this...

Thoughts and suggestions for further troubleshooting would be appreciated.

Thanks a lot.

Any update on this? I'm having the exact same problems with my 2000 Pathfinder. Starts up fine when cold but upon a warm startup I get the terrible misfiring with or without a load on the engine. Once I start driving it seems to go away pretty quick. I did get the P0325 code and it showed up twice on one reading with OBII scanner.

I've read quite a bit about the knock sensor and from what I've read, it seems that the knock sensor will NOT cause a SES light but I am getting it when the misfiring is happening. I'm really just trying to to get this thing running right so I can sell it so I don't want to spend a bunch of money fixing problems that may not be the source of this misfiring.

Where should I start? I've heard O2 sensors, Distributor, Throttle Body clean up, KS relocation, etc. What's the best recourse here?

Thanks everyone.

After checking all of the items I mentioned, and doing the major tune up noted, the problem got worse. I associated it with the warmer weather (since the problem had been minor during winter and only on warm start). I completely isolated the tank/vapor system with no change. I concluded that it was bad injectors. Since the engine code pointed to cylinder #2, I hit that injector with a spray of liquid air (can upside down, to send frozen vapor to the injector coil)--which solved the problem until that injector warmed up again. I bought a reasonably priced set of refurbished ones on ebay (from the seller who goes into great detail about each brand and the various nuances in rebuilding them). The local shop charged me $200 to install the whole set (which is a bargain, since you have to pull the intake plenum to get the fuel rails out of the way). Worked like a charm ever since. If yours feels rough at hot start/idle, ragged (with flashing CE light) when driving right away, and smooth after a while or when cold, that could be the problem. Again, though, I did have a code pointing to one cylinder misfiring. In any case, I would start with a close look at all vacuum lines, since any cracks can cause the mixture to go lean or sense improperly. That could cost you $5, if you are lucky.

Just got done with the same issue on my 98 qx4. P0301 code cylinder 1 misfire, i replaced the fuel injector in cylinder 1 with an injector i pulled from a 99 nissan quest at the junkyard and it fixed it. I bought a new fuel injector for the same cylinder 2 years and 12,000 miles ago and it just went out somehow. Of course right after the warranty. Hope this helps someone instead of racking your brain over a vacuum leak like i did after reading this forum