p0305 & p0171 | Ford Explorer - Ford Ranger Forums - Serious Explorations
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p0305 & p0171


June 17, 2003
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City, State
Palm Harbor, FL
Year, Model & Trim Level
02 Explorer XLT
P0305 is misfire in cylinder #5.
P0171 is system lean in bank 1.

The engine in question is the 4.0 SOHC in a 98 Explorer Sport. I've done some searching about the 00M12 ONP and whatnot, and I'm not sure if that's the fix I need. Besides, I have somewhere around 72,001 miles so I wouldn't be covered. When those o-rings go bad, it seems to throw both P0171 and P0174. I haven't had P0174. The car is idling rough and misfiring like crazy under acceleration.

I thought about changing the plug and wire for cylinder 5, but a bad plug or wire wouldn't explain the lean condition on bank 1, would it?

My IAC has been making noise intermittently as well, but I don't see how a problem with it (or the MAF) would only affect cylinder 5.

Any suggestions?


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If cylinder 5 is on bank 1, I dead injector could cause both of those problems.

If only one part of the o-ring goes bad, it can also make only one bank run lean.

I could try some injector cleaner I guess.

By the way, this all started happening while towing a trailer from Mississippi to Florida (a 10 hour drive). It started making a rattling noise during acceleration first. Then, the misfires started shortly after that, but I was able to limp home by shifting manually (to keep the rpms about 2k) and accelerating very gently.

I think my best course of action may be to take it to the devil, err, I mean dealer and see if I can get the 00M12 and 01M01 work done, as well as a new IAC.

Any other suggestions?


Oh, I forgot to mention something else I found. There is something right underneath the IAC that has 2 hoses coming into it, and an electrical plug with a few wires. One of the hoses was disconnected. I reconnected it but it didn't make any difference. Does anyone know what this part is?

So, no one else has an opinion? Bad injector or leak?

Does anyone know what the thing is that's right underneath the IAC with 2 hoses going into it?


Scott..I just read your questions.....I am having the same problems....did you find out the cause?