A 96 Maxima recently came into my care. The Check Engine Light was on when I got it. Codes (0304 Knock Sensor) and (0302 EGR Hi/Low Flow) were stored in the ECU. The car had 130,000 miles on it. No "blow-by" from crank case, no smoking and not consuming oil. It had an intermittent "pulse" or misfire when in drive and stopped. Idle in park was smooth, unaffected. Light throttle produced power surges and until you stomped on the gas it was difficult to get it to any speed. When trying to accelerate from 30 to 60, power was non-existent until you pushed the throttle so hard the transmission would kick-down into 1st or 2nd and nearly redline the motor. Attacking the knock sensor first, I checked the resistance. It was completely open, no resistance at all. I put a new knock sensor ($120.00) in. I checked the EGR valve by sucking on the hose and felt the diaphragm raise and hold without leaking. I assumed it was functioning, assembled the parts and reset the ECU. The symptoms remained unchanged. The (0304 Knock Sensor) code never returned. The (0302 EGR Hi/Low Flow) code did return. So I put a new EGR valve in. After removing the old one, I inspected it closely and saw no reason for it to malfunction, but I replaced it anyway. When I was installing the new EGR valve, I noticed the supply pipe from the rear exhaust had some exhaust debris in it. I removed a small piece of debris and assembled the parts not giving it much thought and reset the ECU. This also had no effect on my issues, the symptoms still remained. I decided to check fuel pressure and compression. Both tests were perfect with little to no deviation from specs. Attacking ignition components, I started with spark plugs. When I pulled the old ones out they looked fine, but they were the cheapest plug you can buy- $1.99 Champions I think. 6 new Nippon Denso's ($7.99 a piece) went in. I noticed the rear bank coil packs had burn marks on one side of them. At the time I did not know for sure they were burns because they are so close to the intake I thought they could have been scuffs from rubbing and vibration. It did not appear that the front bank coil packs suffered this problem. Using my Fluke I tested the resistance of all 6 coil packs across all terminals. All 6 coil packs seemed to be really close to each other with no huge deviations. The test was inconclusive, so I re-assembled the parts. The new spark plugs had a small effect, the "pulses" or misfires were fewer, but still present. I considered the rear bank coil packs with burns on the sides as my prime suspect. With the engine running, in drive, park brake set and hood open, I got out and looked at the coil packs in complete darkness (Dont try this at home!) and saw the unmistakable blue colored arcing to the intake manifold, which wraps tightly around these high voltage devices. This would explain the burn marks. New coil packs went in the rear bank. 3 ignition coils @ $70.00 each...ouch. Again, I reset the ECU. The surges during acceleration dissapeared, and taking off did not require heavy throttle and harsh kickdown revs to make it move. But the "pulse" or misfire at idle was still there. Half of my problems had dissapeared. The (0302 EGR Hi/Low Flow) code came back shortly after. With nothing left but intake seals as suspect, I decided to put new upper and lower intake manifold gaskets in. When I took the EGR piping off I discovered a lot more garbage was clogging the line than the little piece I pulled out previously. The new EGR valve had some collected in it as well. I found the plenum was severley clogged with carbon and deposits where the EGR pipe dumps it in at the rear of the intake. Both EGR pipes, upper and lower manifolds and throttle body were thoroughly cleared of build-up and cleaned. New gaskets for the intake upper and lower, Throttle body, EGR were installed. After re-assembling the intake system, I again cleared the ECU. Bingo!!! The "pulse" or misfire was gone, and never returned. The throttle response and smoothness were dramatically improved. All of my problems were resolved and the car is a pleasure to drive.
After enjoying a Check Engine Light-Free Maxima for a few days, the damned thing lit up AGAIN...........(0302 EGR Hi/Low Flow) code. I really doubt there is any problem with the EGR system. The engine is running fine. Smooth and responsive throttle and with no misfires.
The only thing I can think at this point is a bad 02 sensor. Looks like "njmodi" is suggesting the TPS of the MAF may be bad also.
Does anybody have any suggestions?
Please Help!!! -Adam