I pulled codes on 2004 intrepid. the codes were po172, po174 and po175. The car has no [maf] sensor has a rough idle at startup. It also has a miss when in gear with foot on the brake. It acts like it wants to stall at stoplights. It is fine while driving. I have changed the o2 sensors and changed the spark plugs. The crank sensor has also been changed in late 2007.
FWIW P0172 and P0175 are system too rich codes whereas P0174 is a system too lean code.
A stuck open EGR valve will cause rough idle when it supposed to be closed, but will work fine at speed where it is supposed to be open. I’m sure that a stuck EGR valve could cause fuel mixture problems to be reported. I’m not so sure that both too rich and too lean would be a plausible result.
Could be lots of other things of course.
I’d look for a vacuum leak somewhere. I vacuum leak will cause rough idle, and will confuse the heck out of the computer. The computer sees too much oxygen in the exhaust and richens the mixture to compensate. But since it really wasn’t too lean before, now it’s too rich—so the computer leans it out–lather, rinse, repeat.
I think a bad EGR could indeed cause this, but it could be a vacuum leak anywhere. I think some of these engines had problems with leaky intake manifold gaskets, so this could also be your problem. (though they didn’t have the GM problem of coolant getting into the oil from this)
No EGR on 04 intrepid. I checked for vac. leaks, found them in the elbow on pcv valve. It was very soft with cracks, replaced elbow and it stopped the rough idle. Would inexpensive gas cause the codes po172 and po175 to come up? or is it something else?