Expedition running too lean

[parkerspark]

I have a 1997 Expedition, the check engine light is on and it is idling low. I took it to autozone and they checked it on their machine said thay it is running too lean, it could be MAS or O2 sensors going bad? I had someone else tell me it could be fuel filter, and someone say it could be dirty injectors. Any ideas? It is running rough and shakey at stops. Has not died, but quivers like it is going to. I don't want to get taken to the cleaners so any help anyone could give would be great!

[way2old]

How long since last tune up? Was fuel filter changed with tune up? Lean condition is caused by low fuel pressures or a vacuum leak in the engine.

[parkerspark]

the fuel filter was changed about a month ago, but it didn't help. what else is involved in a tune-up? What does a vacuum leak mean? What about the low engine pressure, how do I check these things out? And more inportantly, how can I fix the problem?

[way2old]

Do you remember the codes? Were they P0171 and P0174? A fuel pressure gauge is needed to check the fuel pressure. A vacuum leak is where a hose is loose or cracked allowing the engine to suck outside air into the engine that is not metered through the Mass Air Flow Sensor. A tune up consists mainly of filters, plugs, and wires if they are applicable. The MAF can cause these codes if it is reading the wrong amopunt of air that is going into the engine. The O2 sensors are the last place to look for this code. If you don't have the tools needed, it may be best to take it to a shop. If you want to buy the tools to diagnose, it could cost more than having a shop fix it. A scanner that will read the sensor parameters will cost close to 400$. Let us know and we will help if possible.

[parkerspark]

Thanks, that gives me something to start with. Now to add icing to the cake, this morning I went out to start it up and I live in Oklahoma and the temp. was 4 degrees this morning (my car is garage kept, I made sure I had enough antifreeze), but it wouldn't stay started unless I kept my foot on the gas pedal. As soon as soon as I took it off, it died. Could this be related to any of these other problems or something new??? Maybe cold? Thanks for your help!!

[way2old]

The low idling you mentioned in first post may be related to the dying. The Idle Speed Actuator is a known failure item on these vehicles. Did the vehicle run OK after it warmed up some? If it did, the idle speedactuator can be cleaned. If it dies every time you stop, cold or warm, replace the ISC.

[parkerspark]

Thanks so much for all of your help. Hey do you think replacing the throttle positioning sensor could help? I got a MAS and tried that, but it didn't help, someone at autozone suggested the TPS. I got one but haven't been able to get the old one off yet. It only has 2 screws holding it on, but the bottom one is a b****. After 2 hours I was too cold and frustrated, I'll try again tomorrow. Thanks.

[BMFer1]

Don't go throwing parts at it. Check it out. I bet you have a vaccuum leak. Very common failure area on this truck is the pipe from the pcv valve to the back of the throttle body. There is a 90 degree rubber boot on the back of the throttle body that commonly fails. Follow the pipe from the pcv valve back there with your hand. Bet you'll find it is dry rotted & cracked, especially if you've never replaced it. New assembly is about $30 from Ford-comes with new pcv valve, pipe, & rubber.

[TheMailman]

For months I had a CEL on my 97, 4.6L, and codes P0171 and P0174 (running lean on both banks). Would idle rough at redlights and finally began stalling. I noticed a hissing sound under the hood (right side), and finally found a broken vacuum hose to the PCV valve on the right valve cover. Repaired the hose, and no more CEL, stalling, etc.

[carlos80]

Originally Posted by BMFer1

Don't go throwing parts at it. Check it out. I bet you have a vaccuum leak. Very common failure area on this truck is the pipe from the pcv valve to the back of the throttle body. There is a 90 degree rubber boot on the back of the throttle body that commonly fails. Follow the pipe from the pcv valve back there with your hand. Bet you'll find it is dry rotted & cracked, especially if you've never replaced it. New assembly is about $30 from Ford-comes with new pcv valve, pipe, & rubber.

a vac. leak would cause a higher than normal rpm he said his has a low idle, just take it to a ford dealer they can run a diagnostic for typically 80 bucks then you can go ahead and perform the repair yourself

[Redwanr50]

Check on the back of the intake manifold. There is a vacuum line that tends to go after about 80-90K. Mine went this past summer and the symptoms were the same. The piece is a Ford item and not too expensive. I believe it was about $35.00. It includes a few other vacuum lines.

[jacobs98]

My 99 did this same thing. check engine light on wouldn't idle at start-up without keeping your foot on the gas. Then sometimes it wouldn't have a problem at all. My codes were P0401 and P0402. I replaced the DPFE sensor, 100.00 at Ford, and they recommended another sensor, I can't remember the name but they said their techs always do them in pairs. It cost 28.00. I put them on about a month ago and have had no more problems.

[bearcat329]

look at the vacuum hose directly under the idle air solinoid, back of the intake manifold, on the passenger side, the 90 degree rubber boot will rot out and cause a vacuum leak, happened to me, it's part of the EGR system
hth
Rick, Ore

[waxMFD]

Excellent, i just bought my hose assembley and im putting it on tomorrow. I have a question though. The line branches off to 2 once it leaves the pcv valve. One line goes to the IACv, where does the other go? Is this thing hard to replace?

Update - I just replaced the PCV hose assembly and my truck runs fine now. There was a hole on the front 90 degree rubber boot closer to the PCV valve. I erased the codes and later on I will run the computer again to see if anything pops up.

[AutomotiveAce.com]

Need some help:

I have an 03 Ford Expedition (4.6L) and the rubber elbow on the backside of the throttle body that connects to the PCV Valve, has a whole in it! Does anyone have any ideas as to how to get it off to replace it! Thanks for the help.