Ruff idle when cold runs smooth when warmed up getting bad mpg was told could be idle speed sensor replaced mass air flo sensor egr valve and all o2 sensors diasonitic codes come up as running to rich on left and right bank

The regulator is on top of the engine along the gas line. It has a vacuum line on top. Start the truck and pull the vacuum line off the regulator. If fuel comes out of the regulator, it has failed. You can run pretty rich with a busted regulator-especially at idle.

P0402 Exhaust Gas Recirculation Flow Excessive Detected A code P0402 most likely means one or more of the following has happened:

• The DPFE (differential pressure) sensor is faulty and needs to be replaced
• There is a blockage in the EGR (most likely carbon buildup)
• The EGR valve is faulty
• The EGR valve may not be opening due to a lack of vacuum
• Solutions
• With a P0402, it is common for people to replace the EGR valve, only to have the problem return. The most likely solution is to replace the DPFE sensor.
  
  • Check the voltage at the DPFE sensor both at idle and when the EGR is open
  • Replace the DPFE sensor

has your check engine light come on and stayed on after changing o2 sensors. I had a bad tempature sensor on my 2006 silverado and i replaced all four 02 sensors they were showing as bad and then i got a code that said catalyst system inefficient bank 1 and i replaced that catalytic converter and cleared my engine code and was able to go through emissions. but you might have to clean your throttle body check your plugs and wires . if you have a distributor check the cap and rotor button. you also have an egr valve that can get cloged up or go bad and a pcv valve it can be a host of things . if your mass air flow sensor is bad it could cause it to run funny . if your tempature sensor is bad it will not tell the engine it is warm and it will run rich and that will eventually cause your plugs to foul and your catalytic converter to get backed up and your o2 sensors to get carbon build up on them . my catalytic converter looked like it was starting to melt out the honey comb inside . hope this helps

If the CO, HC, and O2 readings are average, then I still suspect the ERG is not being controlled correctly. The EGR should be cold at idle because the EGR ruins the engine vacuum at idle, so must be shut off. And get hot at mid range speed. You can usually feel it with your hand. If it is not opening, then try to manually open it. If it is vacuum, then put a vacuum to its hose port directly. It is it electric, then hot jump it. It is does not cause idle to drop, it is frozen or clogged.

If CO, HC, and O2 readings are below average, then the engine is just running too lean and that gets too hot. Check the sensors, temp, O2, an air mass. An ohmmeter reading of 0 or infinite is bad. The air mass and O2 sensor often are just dirty and need cleaning. PCV foam on the air mass sensor, and carbon on the O2.

You have problem with idle air control valve, it's mounted on throttle body, easy to replace.

it sure sounds like you have an EGR problem. This valve controls the flow of unburned exhaust gases and re-routes them too the intake to be re-burned. This valve is usually open at highway or cruise speeds. Not usually open at idle. If this EGR valve is open at idle, you get a rough running for sure just like a mis fire and will smooth out as your speed increases. I would get that checked out and if faulty, replace. Please keep in mind that this part is quite expensive new, but it is electrically controlled. good luck!

yes an o2 sensor can cause those symptoms so can a minor vacuum leak --bad ignition wire -clogging fuel filter --sticking egr valve etc.

I had same problems w/ my 99 Chateau 5.4L. EGR-Ensure port into intake and pipe from exhaust are clear using low pressure compressed air. Pull vacuum on EGR diaphram and ensure it opens and closes smoothly. If this checks out then problem is probably in the EGR sensor (mine had both ports and hoses clogged w/ aluminum corrosion from the sensor, cleaned out hoses and lines to exhaust pipe w/ compressed air, ended up having to change the sensor). IDLE AND O2 SENSOR- Caused by vacuum leaks in the PCV line (line is plastic wrapped w/foam insulation; was cracked under the insulation; both rubber end connectors at manifold and pcv valve were softened, collapsed and leaking; allowing excess air into the manifold after the mass air flow sensor which throws off the O2 sensors. engine computer does not read O2 sensors until after engine is warmed up which is why idle is fine until then).

Try replacing the coolant temperature sensor for the injection system.

have it scanned,ck' tps sensor,mass air sensor,idle air sensor for output...kev-mn.