I checked the TPS and MAFS, replaced the O2 sensor. No codes.
Starts and idles fine. I have an exhaust leak in the tube that runs to the EGR valve at the Exhaust manifold . could that leak cause the engine to run bad? What else could it be?
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Okay, lets start with you checking the fuel preasure regulator, this is a common problem with these the regulator leaks and the vac line connected to it starts sucking gas into the intake, this causing it to run rich and depending on how bad the leak is it will stall engine at idle, remove the vacuum hose from regulator and start engine then see if gas shoots out the vac connection on the regulator, if it does then replace regulator, hope this helps.
This in an extract from an article on O2 sensors from an article at www.autotap.com:- 'The O2 sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in the exhaust. The signal from the O2 sensor tells the computer if the fuel mixture is burning rich (less oxygen) or lean (more oxygen). A lot of factors affect the richness or leanness of the fuel mixture, including air temperature, engine coolant temperature, barometric pressure, throttle position, air flow and engine load. Other sensors monitor these factors too, but the O2 sensor is the master monitor for what's happening with the fuel mixture. Problems with the O2 sensor can throw the whole system out of whack.'
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).
was the code for rich or lean? may try cleaning mass air flow sensor. it is in the air intake tube and has a flat wire connector. take out of tube and take four torx bolts out and clean with mass air flow cleaner or brake cleaner and put back in when dry. or it could be a bad wire on the o2 harness. look for chaffing or broken wires in harness by o2. also could be the exhaust system has a slight blockage. could also be some other things but try these first.