1998 Windstar 3.0 with PO171 & PO174

I've spent hours going through the archives, but virtually all of the info I've been able to find about the OBD trouble codes (PO171 & PO174) has been for the 3.8 engine, or for different years than my vehicle. I'm hoping one of you can help me out (please!!!).

My 1998 Windstar has approximately 83K miles, and the SEL light came on last week. A trip to Autozone yielded the OBD codes. I immediately changed the fuel filter (no improvement). I then checked fuel pressure (40 psi with engine off, 36 psi with engine running) and vacuum (16 in. hg at idle). All those readings are normal. So I cleaned the MAF with intake cleaner. No change in service engine light, but the car is starting easier now (the only symptom I had seen--aside from the SEL--was harder starting). I hate to spend $100 on a new MAF unless I can be confident that the old one has failed.

This car has been outstanding up till now, and I'm hoping this won't be a bear to fix. Any suggestions would be greatly appreciated.

Thanks in advance!!! (and thanks for this wonderful message board!)

I figured it out and fixed it. Problem solved.

What was the fux to the problem ?

Sorry "fix" to the problem.

The MAF cleaning worked, but the OBD codes did not clear until I disconnected the battery for about 30 minutes. Apparently some OBD codes will clear automatically when the computer detects that the problem has disappeared, but this does not appear to be the case for these codes. Anyway, the car is running fine, the fix was easy and cheap, and I'm planning on cleaning the MAF whenever I replace the air filter in the future.
I hope this helps!

Since my last posting, I had to clean the MAF again. And now my SEL light is back on (again). Is there another possible explanation for the P0171 & P0174 codes? Keep in mind that this is a 3.0 (and not a 3.8) and the MAF cleaning seems to work for two or three weeks before the SEL light reappears.

Thanks!

Well Anytime you get a 171/174 code you are getting air into the intake that the computer does not "know" about. This is due to bad readings from the MAF or air entering the system after the MAF. I think that cleaning the MAF has made a slight compensation that puts the car into the okay zone, albiet very barely, and then of course the failure re-appears. Of course the standard 171/174 fix does not apply to the 3.0s as you are no doubt aware.

I think you are going to find that you have a small vacuum leak due to a loose vacuum hose, PCV valve, gasket.....I would look for this first.

Hopefully it will just be something simple but it may take a while to find.

I'll run a vacuum check and look to see if I can spot any irregularities in lines, connections, PCV, etc. and will let you know if I find anything.

Thanks!

Some minor corrections.

Disconnecting the battery DOES NOT clear any codes. The CEL goes off because the computer's adaptive memory and emissions subroutines are cleared, the CODES are still there. Also, there are active "trouble" codes, and "emissions" codes, active codes will also cause a CEL, and if an active code did cause the CEL, disconnecting the battery will not get the CEL to go off.

If cleaning the MAF works for a few days, is the sensor getting dirty that fast or is somehting else wrong? Also, do you disconnect the battery when you clean the MAF? If so, cleaning the MAF is not causeing the light to go off, disconnecting the battery is. It is RARE for a MAF sensor to fail, it does happen.

Cleaning the IAC valve is a temporary measure at best that sometimes works, and often does not. Eventually, most likely soon, you will have to replace it. CLeaning is NEVER a long term fix with these.

16 inches is within the accepted limits for vaccum... barely. I would look for a vacuum leak somewhere because you really should be seeing 18 in or better with that engine.

Thanks to Modmech and Dngrsone for your replies! I also thought 16 in. of vacuum seemed low, but appreciate your confirmation. The vacuum leak scenario seems very plausible to me, so that's where I intend to focus my energies this weekend.

With respect to the MAF, I have a clean air filter, so I am thinking that the CEL is coming back on because the codes are never clearing (and not because the MAF is getting dirty). I have disconnected the battery in the (mistaken) belief that it would clear the trouble codes as well as shutting of the CEL. Apparently this is not the case--although the light does go out and stay out for two or three weeks.

At this point I will start by checking thoroughly for a vacuum leak. Virtually all of the hoses are original, and I wouldn't be surprised if one (or more) had deteriorated. If that doesn't do the job, then I'll take a closer look at the MAF.

Thanks again, and I'll be sure to post a follow-up!

You guys were correct! I have a vacuum leak. I used my Mityvac pump to check all the lines, connections, etc., and everything was tight except what looks like an evaporative cannister purge valve that is located on the firewall. Do any of you know what that device is for, what it is called, approximate price, etc? It will not hold vacuum, so I temporarily disconnected it and plugged the line. Now I will be interested to see how the car behaves with the vacuum leakage stopped.

Thanks for all your help!

It is called a Vapor Management Valve (also known as a Canister Purge Control Solenoid), $53 online at Autopartsgiant.com.

It allows the engine to suck the gasoline vapors out of the vapor management canister. It doesn't usually go bad, and the fact that it doesn't hold vacuum in a static environment doesn't mean it's bad... the EGR Solenoid won't either. SO i'd hold off for a while and make sure the CEL doesn't come back before purchasing one.

My wife just informed me that the car has been very difficult to start on cold mornings--it stalls unless she presses on the accelerator to keep it running. Anyway, this morning (despite temps in the 20's) the car started great (with the line to the vapor management valve plugged). Also, when I checked the EGR solenoid valve yesterday, it helf vacuum with no problem--but it sounds like it should not have done that, based on your comments.
Please let me know your thoughts, and thank you very much for all your help!!!

Well, all I can say with certainty is that when I checked my EGR solenoid, it wouldn't hold a vacuum, nor did a brand new one. According to the Chilton's, your are supposed to lightly blow into the ouput tube (that goes to the EGR valve) and if it allows air through it's bad.

I did replace my VMV and the replacement that I got didn't hold a vacuum, either. It is entirely possible that the new VMV I got was bad, but I haven't found any problems to attribute to it if it is. YMMV.

I'm not sure if it was the new vacuum management control valve (Motorcraft part# CX-1669, purchased from O'Reilly's for about $40) or the new PCV, but the car is running like a champ now, and the CEL is staying good and dark. The car starts great when cold, idles smoothly, and exhibits no nasty behaviors.

If I had to bet, I'd say it was the PCV that had been causing the problem.

BTW, I checked the new vacuum management valve, and it doesn't hold a vacuum either (just like Dngrsone said), so you were right on the money.

Thanks for all your help!