Engine compartment is making a rattle sound. It's coming from the front, and can only be heard when you're paralell with the fan or driving the car. It's faint enough that it can't be heard standing 5 feet from the car with the hood open, but as soon as you get in the car or get over the engine compartment it can be heard.
The only time the rattle can be heard is during low idle. At high idle, light or heavy acceleration and deceleration, and high idle in park it makes no noise. At low idle in park or at a light it makes noise intermittently. The engine has *lots* of power, and is running perfectly. The worse the noise, the lower the engine RPM's go and the engine itself shakes slightly with the noise. At low idle when moving without the foot on the pedal, it's sometimes enough to cause the car to completly stall out.
The waterpump, radiator, power steering pump, sparkplugs, wires, and distrubutor cap have all been replaced. The emissions system has been completly checked and fixed; all systems are functioning properly. The car is driving better than it ever has, it just has this one problem.
Additionally, it's setting code 13 and 21. The hayens manual says it's the Throttle Position Sensor and Oxygen sensor that need replacing. Before changing out the spark plug wires, the engine was missing at low idle and during light acceleration and was setting no codes; after changing the plugs and noticing several had cuts that were grounding out, the engine runs better than it ever has, but is tripping these two codes. It has intermittently tripped these two specific codes in the past, however they seem to pop up after a repair and go away after the next.
Finally, I pulled about 3 quarts of oil and put 6 into the engine last night and changed the rear differential fluid (it was time). Before, the oil was full and I have streakmarks by the headgaskets which means I likely have a headgasket leak. None of the plugs I pulled during the replacement had oil on them. No oil light was set. I have yet to check the level this morning, but I'v never seen the car leave an oil puddle anywhere and the level has always stayed consistant whenever I check it (usually in the morning). It doesn't smell like the oil is burning and the radiator fluid has no oil in it. The oil has no metal filings in it, but was mildly contaminated (PCV was plugged for awhile until I hooked it up right).
Yea, it does make vibration. I am unsure if it is or isn't the fan, but I suppose torquing down the bolts more couldn't hurt. I don't believe it is, however, since the issue seems related to RPM and heat. For that matter of fact, I probably should check the belt tension as well.
47,000. Engine was replaced with remanned once before, and the trans changed out from a THM-400. That's what the previous owners said and I'm inclined to believe them from what I'v seen. Before that the car has 130,000 miles on it. I'v mabye put on 1500 miles in the last few months.