I have 97 f-50 and the check engine light came on. Took to local shop and they have replaced plugs, (Bosch) Plat plus, installed new plug wires, cleaned fuel injection, air filter, chamged oil & filter, replaced pcv valve, cleaned maf sensor, replaced throttle body vacuum line ( one with elbow and goes back to pcv) checked all vacuum lines for leaks, and the truck still runs rough at idle. Also does not seem to have same get up and go. The codes they pulled (171-174) when light was on. I have read numerous threads and do not trust dealership so I am trying to figure out what to do. Plan of action is to clean IAC and throttle body. Any way to clean throttle body with taking totally off the truck? I bought spray cleaner and took off breather in front and it clearly says do not spray cleaner on front? Also , numerous threads say scrap the bosch plugs and use motorcraft plat plugs, I looked up plugs on motorcraft site and they sayAGSF42FM gapped at .054. The owners manual says .052 ? If all else fails is there a way to test o2 sensors rather than just start replacing 2 fronts and then move backwards. I am on a tight budget and trying to fix myself.......help ?ot

 

How many miles are on your truck? If it's more than 80k, it's probably your O2 sensors. Mark M

 

94,000 miles......Replace all 4 ? How can you test them to see if only one is bad. also replaced fuel filter which I omitted from above.

 

Fryguy,if it were me,ide install Motorcraft double platinum plugs,gapped at .054 along with a set of OE Motorcraft wires. I would then put on a good quality fuel filter.Code 171 is an upstream 02 sensor that needs to be replaced on one side,and code 174 is a downstream 02 sensor that needs to be replaced on the other side.
Pull your IAC valve off,get some CRC throttle body cleaner,spray out the IAC,let it set and soak as you take the CRC TB cleaner and a soft bristle toothbrush and clean that filthy,dirty,nasty TB! Trust me on this one,I just did it 2 weeks ago and you cant even tell my motor is running at idle!Oh,BTW,you need to disconnect the negitive cable before this process!Good luck and keep us posted!

 

OK in review here lets try and find a logical starting point to work from. If I read your post right, all plugs and wires have been changed. I would first suggest that you consider 2 areas of potential problems. I'm going to talk about the plugs last as I doubt they are the cause of these codes but in order of logic and history they do need some thought at some point. Since the code is indicating O2 sensors, and the mileage concurs with this possibility, my first doubt was why the shop hasn't changed them at this point. Before I went out and paid $75 a whack for 4 new ones, here is what I'd suggest. Swap O2 sensors with each other. Rather than go into a long discertation on O2 sensors here the bottom line is, the upstream O2 sensors work harder than the downstream ones. The sensors are the same. I personally would change the position of the sensors (swap front to back on each side). Your upstream now becomes your downstream and vice versa. If they are in fact bad, your code should now move to indicate the new position failure mode. You do this simply to confirm that the O2s are in fact needing replacement. If they do, then yes I'd replace all 4 of them. If the code does not change, then I'd start looking at a rich (or lean but not as likely) condition being caused back in the process more. Since I will take at face value that the vacuum has been checked and found to be tight, then yes its time to consider your throttle body and idle speed control circuit. Since you were having problems before they changed the plugs I would likely think that your new plugs aren't the cause however if cleaning of the throttle body and idle circuit didn't fix it, then I'd move on to the plugs as being a bad choice. The Bosch plugs have had some issues in these ignition systems. I don't know why it is, but some have confirmed beyond a shadow of a doubt that some of the Bosch plugs work and some don't in these ignitions. Stay with the Motorcraft plugs and stock ignition on this one. Ford did a VERY adequate job of designing a good ignition system here.

You have one other area to consider. The EGR valve can get carboned up pretty good on these. When that happens it can fault the fuel mixture sense circuit. It is an easy fix to remove and clean the carbon from the valve and the carbon it deposited in the engine. A good spray cleaner would do the job. You can avoid this step completely and in fact I'd recommend, a good overall power cleaning of your fuel system. The shops use a pressureized additive system they introduce into the TB and run a specified amount through your engine while its running. BG products does an excellent job of restoring your whole fuel and delivery system to like new condition. Money well spent regardless, but also can save you a lot of "hunting" of expensive repair possibilities such as what you are already in the midst of doing here. There are several choices of these and I have heard good things about SeaFoam and others. I can only atest to BG from my personal experience. The point is, it can eliminate the root cause of the fault, and also give you the peace of mind that it can't be caused from a dirty component faking you out.

P.S.
Make sure the computer codes are cleared before you swap out components so you can start with a clean computer code.