Hello everyone, I bought a 1997 Explorer XLT 4.0 OHV a few days ago. It was a single owner vehicle. I paid 800 bucks for it. Only down side I saw was the number of miles on it. It still has the original engine and transmission and they have about 338k miles on them. This thing has been taken care of. It runs great for the amount of driving thats been done in this thing. Things that I noticed was a bit of a rough idle and a little bit of bogging down on the accelerator. Soooo now a few questions. First thing I did was get the codes. I had P0171 and p0174 along with about 4 cylinders with misfires detected and a few other codes. I checked for vacuum leaks as best I could. I figured before shelling out all the cash for 4 O2 sensors I'd replace the intake manifold o-rings. I bought a pack of upper intake o-rings. Question 1: The pack came with 6 o-rings but I only saw places for 3... where the hell do the other 3 go?! After I got it all back together it drove for about 18 miles before P0171 and p0174. No cylinder misfires yet so that was a good thing. Today I replaced the PCV hose and the 2 pressure hoses for the EGR valve. I hit the throttle bottle with a bit of MAF cleaner(they had no Ford safe throttle body cleaner). I put about a half a bottle of Seafoam in the gas tank and the rest I sucked into intake through the Brake Booster hose. This thing seems to run ALOT better. I did notice that the temp gauge wasn't coming up much on this thing. So I put a coolant temp sensor on it... I think its the wrong part, should have been the sender unit which I will pick up tomorrow. Question 2: How likely is it that the old sender is dead or is it just the thermostat stuck open. Question 3: Anything else I should watch out for or expect on an engine with this many miles? Thanks for reading and glad to be apart of the forum. Hope I can contribute as well!