I have an 06 Pac 3.5L 104K. Plugs and filters were replaced at 90K. I got a PO420 code that came up and then turned itself off (car running great). Came back on about 3 weeks later. Seems to be getting bad gas milage. About 2 weeks later it starts running real bad but only when engine is cold. Starts chugging and stalling out. When it's hot, it runs good but it looses power as if the rev limiter kicks on when you hit the gas to pass a car on the highway.Then a few more codes came on. PO404 (EGR circuit) and PO129 (low barometric pressure), and PO108 (MAP sensor high input).
I assume that the cat converter needs replacing. I can erase all the codes except the PO129 which will not erase with my scan tool. Anyone know where this code comes from?? Would a bad EGR valve cause the engine to run like this or would the EGR code come on due to the cat converter being plugged up and making it run like this? I can hold my hand over the tail pipe for 5 or 6 seconds before it builds up enough pressure to blow past my hand. I would think that it should take maybe 1 or 2 top's if there wasn't a restriction???? Any thoughts??
I haven't done the repair yet but I did get a new Walker direct fit cat for $120 on line. Arrived today. Dealer said that this is the same brand they would use and sell to me for $600+. I'm going to replace both O2 sensors while I'm at it and hope that this cures the problem. Any thoughts or comments would be greatly appreciated.

 

P0129-BAROMETRIC PRESSURE OUT-OF-RANGE LOW
When Monitored: With the ignition key on. No Cam or Crank signal within 75 ms. Engine
speed at less than 250 RPM.
Set Condition: The PCM senses the voltage from the MAP sensor to be less than 2.196
volts but above 0.0392 of a volt for 300 milliseconds.One Trip Fault.

POSSIBLE CAUSES
IAC SIGNAL CIRCUIT LOW
IAC SIGNAL CIRCUIT HIGH
INTERMITTENT CONDITION
(K6) 5 VOLT SUPPLY CIRCUIT SHORTED TO VOLTAGE
(K6) 5 VOLT SUPPLY CIRCUIT SHORTED TO GROUND
(K6) 5 VOLT SUPPLY CIRCUIT OPEN
MAP SENSOR INTERNAL FAILURE
(K1) MAP SIGNAL CIRCUIT OPEN
(K1) MAP SIGNAL CIRCUIT SHORTED TO GROUND
PCM (K6) 5 VOLT SUPPLY CIRCUIT
PCM (K1) MAP SIG CIRCUIT

 

Thanks for the reply, but I'm not quite sure what you're telling me. What is the IAC circuit? What is all the (K6)?? Does this refer to the PCM? The past couple day's, the car would run OK cold until it get's warm. Now it's stalling all the time after it warms up. It will idle for a bit then run rough and stall. As soon as you give it gas in drive, it immediately stalls. Sometimes even though fully warmed up, idle will run very high for a bit, then slow down and eventually stalls. I replaced the EGR valve because I kept getting PO404. No change, still runs until it's hot then stalls all the time. Cannot drive it. The exhaust smells like it's running rich cold and hot and doesn't appear to be plugged but could this still be a symptom of the cat converter? I did keep getting PO420. How do you check for a plugged exhaust system? I have a Inova scan tool that shows the O2 sensors operation. When it's hot and running, both O2 sensors (upstream and the one in the cat converter) giving the same readings. Shouldn't they be different?? HELP!!!!

 

OK, after a little research, I found out that the PO129 (low barometric pressure) is monitored by the MAP sensor. I did get a PO108 (MAP sensor) code that kept coming up along with the others, so tomorrow the MAP sensor will be replaced. After reading the symptoms that a bad MAP sensor can cause, I'm feeling pretty good about this. It sounds like everything my Pac is doing. We'll see.

 

OK, today I replaced the MAP sensor and the car is running great. All these codes that came up made it hard to pin point the problem. I had about 5 different codes come up, with the first being PO420 pointing to the cat converter. Then EGR and PO129 which doesn't even mention the MAP sensor. Unless you know that PO129 comes from the MAP you'd never know. I wasted many hours looking on the net for detailed information on the codes, searching for a cat converter, checking the converter on my car, installing an EGR valve and the money for the valve and the cat. Why can't these darn vehicles just give you the code from the bad sensor instead of making you figure out all the other codes and possibilities?? It took me all of 5 minutes to replace the MAP sensor and with my rewards card at Autozone it cost me $4 and some change for the sensor. Problem GONE! Please bring back the engines of the 60's!!!