This morning I took a trip about an hour away and my car was running normally. About 30 miles from home it started loosing power. I would push on the accelerator to head up a hill and the car wouldn’t accelerate at all. It was like you had to baby the throttle to keep the car from bucking and slowing as I was going up hills. It continued to get worse and worse as I got close to home. The cars misbehavior became different as I got closer to home. The idle was very high (about 3000 rpm), it would alternate between dying and idling fast and now it will barely start at all. It set the check engine light and these are the codes that it set: P0131, P0300, P0101 pd, P0121 pd, P0131 pd. I thought the first one the #1 O2 sensor seemed like a likely culprit, I changed it and it didn’t make a difference. I’m not sure if I should keep changing sensors or let the shop have a turn at it. Anyone have any ideas?
Do not keep changing sensors - that’s a very expensive way to diagnose. If you have a multimeter and a repair manual for the car (getting these would not cost much) you can probably figure out the diagnosis.
The code I’d ignore for now would be the random/multiple misfire code (P0300) as it is likely the result of the other problems.
P0131 doesn’t mean “replace the O2 sensor” - it means that there is a circuit problem - might turn out to be the sensor, but you just found out the expensive way that it probably wasn’t the sensor. The circuit for that sensor is one thing you have to check.
P0101 refers to an out of range signal from the MAF and P0121 refers to a circuit range problem on the throttle position sensor.
So you basically have what one might call multiple interacting systems problems. Unfortunately when things go haywire like that one thing you have to wonder about is whether or not the computer itself has a problem.
In any case, start with a simple inspection of those wires/circuits. Pull the connectors & inspect for damage/corrosion/contamination etc. Clean them up really well with electronics cleaner and put them back together with some dialectric grease. Pull and clean the MAF with the electronics cleaner as well (or you can buy MAF sensor cleaner which I’m pretty sure is just relabeled electronics cleaner). Take a multimeter to the MAF & TPS circuits - see if the voltage feeds, and resistances are all within specs.
Of course, someone smarter than me might know exactly what ties all of these things together.
If all of that sounds like Greek then you should probably let a shop have a look at it. You need a really good local, independent and you likely need their best diagnostics guy/gal.
Thanks for your response. The reason I just went ahead and changed the #1 O2 sensor was because I had intended to change it at 100,000 miles anyway. The car now has 115,000 miles on it. I do have the manual and a mult-meter. I’ve checked the MAF for the proper voltages but it requires an testing tool to check the sensor itself, measures something in parts per million or something like that. Haven’t gotten to the throttle position sensor yet.
you checked the ignition system? One plug misfiring from a arc-over will cause excess oxygen in the exhaust. The computer will lean the mixture causing reduced power. Does it run ok when it’s cold and starts failing when it warms up? The sensors start economizing the fuel after it has warmed up.
I’ve checked the secondary windings on the three coils. Replaced plugs and wires several months ago. I haven’t tried starting it cold yet.
Thanks to everyone who helped me with this problem. I disconnected the MAF sensor and was able to start the car this morning. I was able to hear a huge vacuum leak from the front with the engine running. There was a 1/2" hole in the upper (plastic) intake manifold where the exhaust gas from the EGR valve comes into the intake. In the process of changing out the intake manifold now. The guys at O’reily’s told me they sell quite a few of these plastic intakes.