Ok, a little background first. I have a 2005 with about 117k miles on it. No mods except for an Injen intake that's been on since day one. Valve adjustment performed at 70k miles and new plugs at 100k miles.

Problem started a few weeks ago. Car was hesitating around cruising conditions 3-5k rpms. Not all the time, just sometimes. Then it threw a code and started stuttering at idle. Code was p0172 (bank one too rich). Stutter started getting worse and hesitation at speed was bad as well. It felt like I lost all power for about half a second. It would sometimes turn off at a stop as well and go into limp mode on occasion.

Took it to a local mechanic which pulled the same code, checked plugs, and looked at piston heads and cylinder with boroscope. Plugs had evidence of running too lean as well as the primary O2 sensor. He suggested that primary 02 might be bad so I bought a new one and replaced it this weekend. Went ahead and replaced the secondary as well b/c the protective tip was broken off in the cat and ratteling.

Put the car back together and it ran fine for a day. This morning, started having the same problem. Hesitation and turning off at stops. Went into limp mode as well. Pull the code reader out and got the p0172 again but I also got a p1129 this time (manufactur air fuel malfuntion). Leads me to think it might be the map sensor. This whole time I've been wacking the sensor as well.

Now, I've pulled up about 1000 old threads for similar problems and codes. Others have replaced everything from the plugs to the coils to the maps sensor and both 02 sensors and still have the problem. One guy ended up with a bad ground somewhere. Most still haven't posted answers or solutions after they went to the dealer. Others get the "it's the hot weather" answer but I know my car and after 117k miles in all weather ranges, it's not the weather.

Any suggestions? I don't want to go on a wild goose chase replacing parts if it's something simple. Thanks in advance.

 

it's normal that rich code causes engine to run lean. i asume you have fuel problem, have anybody ever checked the fuel pressure? (47-54psi)

Also check your engine vacuum with engine fully warm up, no load . it should be at -21" idle at sea level.

 

If you've got a scan tool, see if the MAP Voltage is the same as the BARO voltage with the key on engine off.

 

Roger. I'll check that when I get back to the office tomorrow.

On a side note, I recet the ECU today and let it idle for a few minutes. Seems to be running fine again. Not sure if it will last though.

 

Fuel trim DTC's don't recode quickly.

Basically the PCM is adding or pulling (P0171 or P0172) more fuel than it's supposed too, in order to hit the target A/F ratio.

The PCM is following O2 sensor input to do so. YOu car is running richer than spec, so too high fuel pressure, a leaking fuel injector or jacked up MAP sensor can all cause it.

 

My scan tool didn't have baro or map voltage, just pressure readings. With the key on/engine off, map sensor read between 100 and 117kpa while the baro read nothing.

Also, after resetting the ECU yesterday, it ran fine again for a day. Instead of giving it gas when it bottoms out on idle, I let the engine adjust itself. That takes care of the idle trouble for the most part after the ECU learns, but it's still driving poorly and always hesitates and has terrible idle on startup for about 30 seconds until the ECU adjusts.

Threw a code again last night for p0172B (bank 1 too rich) again.

 

Need a scanner that can read MAP in Volts or time to break out a DMM

 

have a dmm. where are the barometer leads though?

 

Non existent.. The BARO sensor is built into the PCM. Can't check it's votage without a high dollar scan tool.

Have you checked fuel pressure?

 

have you done compression/leak?

my off-the-wall guess would be...hmm...coilpacks maybe? you've actually got much of the obvious stuff covered.