Ok, I picked up my "new to me" 98 Exp XLT 5.4 w/136kmi yesterday afternoon. I drive it home (about 40 miles ) with no issue, then getting off the interstate and driving 45mph (just puttering along) the CEL came on. It still seem to run fine but I pulled into Parts America and ran the codes. All I got was a P0133 - O2 slow ckt response (bank 1 sensor 1). Now, the odd thing I didnt catch, when I picked it up none ofthe radio presets were set Thats not the exact message on the reader but close enough. Since I am absolutely broke from the purchase I cant afford the sensor until payday, I thought it would just run a little rich (it has/had plenty of power). After about 20 miles into my commute I hit the wall of stop and go traffic and then the engine started acting up. It is like the engine is shuddering (its so quiet I cant really hear it but I 99% sure its misfiring). When I let off the gas it goes to a rough idle, if I gun it (not floor it, just press a little harder than norm) it usually takes right off. It is 4 degrees out and I have a 40 mile drive home ( at least 10 of it is stop and go). Are these symptoms of a bad O2 sensor or do I have additional problems? (i.e. do you think it will make it limping home?) It starts at the touch of the key, just running really bad.

 

Also, I disconnected the battery to reset the codes and the CEL did come back on. I assume its till the O2 code but Im unable to get the codes read right now.

 

Most certainly could be O2's. Also could be plugs (due at 100K miles), dirty any filters, dirty Mass Air Flow meter.

At that mileage, you need to take some time and $$ and do some fix er up work. Two new 02's, plugs, clean filters all around, make sure all vac lines are tight, check the PCV valve and hose (another source of bad running/poor mileage), clean out the throttle body. All the basics. Unless there's damage somewhere, it'll probably run like new!

 

Thanks for replying waterman, I just came back from the dealer and did have the oil changed (mobil 1 full syn and a K&N oil filter). I asked for a tranny flush& service and they told me it didnt need it (said it was like new). It was a fleet vehicle most of its life and had all service/periodic maint, it all shows up on the carfax ( the alt, starter, fuel pump, filters, tie rods have all been changed in the last year too). They said my problem was a severe vacuum leak at the back of the engine (the elbow was ok but the tube was bad). The check engine light came back on but they told me to drive it for a week before looking at O2 sensors etc, he said the vacuum leak caused lean condition which the computer compensated for by going to rich and that my cats and sensors are "all loaded up". I am supposed to drive like I stole it for a week to clean it out and they will re-evaluate then. I also got a copy of the OASIS report and it was clean, no missing recalls, tsbs etc. SO, now I am dirving it hard and I'm getting a new code P0303 but it only tripped once and the reader showed it happened at 3300 rpm@75MPH with 14.9 fuel setting/mixture and a whole slew of other numbers that were beyond me. Do you think I should replace the #3 COP even though it only threw the code once?