I am having major issues with my EGR, car runs very rough, NEW EGR, NEW MAF SENSOR, NEW EGR VACUUM CONTROLLER. If I use a piece of foil to bypass the EGR then it works great. Any ideas? 2002 Toyota Camry, V6

Fuel pressure regulator bad. Vacuum operated , pull the vacuum line. Smells like fuel. It's bad .Electronic could a fuel pressure sensor on the fuel rail or the fuel pump control module.

Hi Mark:
My train of thought is along the line that for unburned fuel to get into the exhaust manifold, it still has to go through a cylinder so there is either no spark to light it up, or it's so rich that it's not burning. Have you had a chance to check the plug tips for indicators as to what's happening in the combustion chamber?
Just an Old Dude thinking out loud and typing it down...

It could be several different things causing this, my first guess would be to look at the EGR port going into the intake. Most times it will clog up and can cause rough idling. You must know how to clean it properly, the EGR valve will have to be pulled as well as the throttle body in order to clean it properly. Also, check for vacuum leaks. It could be other things as well but this is where I would start. Hope this helps. Thanks, Allen with Morgan's Auto Repair 912-282-1602 Waycross, Ga.

Stop, DO NOT replace expensive parts or O2 sensor! Ford Explorer codes p0174 , p0401 , rough idle and check engine light on. First thoroughly check all of the hoses and elbows connected to the intake and EGR (vacuum system) for splits, cracks, holes or tears, this could quickly cause these codes and fixes for less than $10. Check all connectors and the EGR valve sensor it could have a crack as well, inspect thoroughly because a split sensor could appear attached to the vacuum hoses but hoses could just be sitting there not actually attached due to a split or crack. This was my problem replaced the EGR valve sensor and the two little vacuum hoses attached to them for $50-60 with in stock parts at the local parts store. Took less than 10 minutes to replace and is easily accessible, the check engine light turned off immediately without having to reset the codes by disconnecting the battery, idle became normal and fuel efficiency better. If you have THOROUGHLY inspected every hose, connector and elbow and found no issues, clean the MAF with electrical contact cleaner ( let dry) and clean the EGR with carbon cleaner. A dirty MAF or EGR could also cause these codes to pop up. If this still doesn't work, then consider replacing the EGR, if that isn't it then try the O2 sensor. Good luck!

What is model year? How long since a tune-up?
With idle issues, check and clean idle air system, see if it helps? Use a gage and check proper fuel pressure, key on engine off. On some ford vehicles, with everything off, unplug the maf sensor, where applicable, take the vehicle for a spin, if it does a lot better, have to check the maf system, that includes, sensor--wiring circuits--pcm.
The basics on a rough idle, is to check for a leak of some kind, fuel--egr--vacuum.
Positive fuel trim at low speed and load, the first thing, look for vacuum leak.

p0401 egr flow insufficient. p0171 system to lean ( bank 1 ). p0174 system to lean ( bank 2 ). common problems that trigger p0401--

• Restriction in the EGR passages, usually caused by carbon buildup
• The EGR Valve is defective
• Lack of proper vacuum or electrical signal to the EGR valve
• Malfunctioning EGR Vacuum supply solenoid
• Lack of proper EGR system feedback to the computer from the:
  
  • Manifold Absolute Pressure Sensor (MAP)
  • Differential EGR Pressure Feedback Sensor (DPFE)
  • EGR Valve Position Sensor (EVP)
  • EGR Temperature Sensor - p0174--
  • In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling also
  • Inspect all vacuum and PCV hoses, replace if necessary
  • Check for a dirty fuel filter and proper fuel pressure p0171- and p0174 are about the same.

The EGR Valve will be most noticable going up hill or under a load ( High Vacuum). Remove the vacuum lines, if you have them and plug,that will take the EGR out of the picture,while you work on coils or other issues.
Clean the MAF Sensor with CRC MAF Cleaner.
Make sure your O2 Sensors didn't loosen up.

PO171-System to Lean (Bank 1)

Air filter cover tight?
All intake ducting tight?
Clean MAF Sensor.--CRC MAF Cleaner
Fuel Pressure Regulator?
EVAP Purge Valve-stuck open?
Vacuum leaks?
EGR System-issues?

Seems your getting a lean O2 Code,because it is trying to correct for a rich condition,as you said.

Is the Throttle Position Sensor-original?

Work on what is driving it rich,my list is a possible.

A code P0134 may mean that one or more of the following has happened:

• Bad O2 (oxygen) sensor
• Bad heater circuit in the O2 sensor
• Wiring or connector to the sensor frayed / broken
• Blown heater circuit fuse
• Holes in the exhaust system
• PCM failure

Possible Solutions The most common fix is to replace the oxygen sensor. But that doesn't rule out the possibility of:

• Rusted exhaust pipe
• Inspect wiring & connector(s) for problems
• Excessive amperage blowing heater fuse (still requires replacement of sensor but also replacement of blown fuse)
• Replace PCM (only as last resort after all other possibilities are covered.

A code P0171 may mean that one or more of the following has happened:

• The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
• There could be a vacuum leak downstream of the MAF sensor.

Possible Solutions Possible solutions include:

• In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
• Inspect all vacuum and PCV hoses, replace if necessary
• Check for a dirty fuel filter and proper fuel pressure

how about a simple tune-up?  Plugs and filters.