I have a 1998 Chevy suburban with trouble codes 172,175 rich on banks1 and 2 and 300 code multiple cylinder misfire. I have changed plugs,wires,cap and rotor and electronic egr valve. Help please .
Next thing comes to mind is 02 sensor, that will cause it to run rich
Yeah after looking up P0172 and P0175 it does not specify 02 sensor, only the vague 'rich on banks 1 and 2 " just like you already know Oben. "fuel trim system" which does include 02 sensors but other components as well.
A code P0172 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 can 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. There could be a fuel pressure or delivery problem Possible solutions include: Inspect all vacuum and PCV hoses, replace if necessary Clean the MAF sensor. 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 fuel lines for cracks, leaks, or pinches Check the fuel pressure at the fuel rail Check the fuel injectors, they may be dirty. Use fuel injector cleaner or get them professionally cleaned/replaced. Check for an exhaust leak before the first oxygen sensor
I have already cleaned my maf sensor, check vacuum steady at 18-20 . New exhaust no leaks in it. At idle runs rough but smoothes out driving and has very bad gas smell out the exhaust.
Hmmm. I looked up P0175, and it says the very same thing, so no need to re post it. I will try another source and see if I can find another fix
This is good. Go read: http://troubleshootmyvehicle.com/gm_P0172_P0175_4.3L_5.0L_5.7L/rich_fuel_tests_1.php....it's a really good article, right on target about your trouble
Also, since those didn't help, I tried P0300 that you wrote and found:..A code P0300 may mean that one or more of the following has happened: Faulty spark plugs or wires Faulty coil (pack) Faulty oxygen sensor(s) Faulty fuel injector(s) Burned exhaust valve Faulty catalytic converter(s) Stuck/blocked EGR valve / passages Faulty camshaft position sensor Defective computer Possible Solutions If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.
However Oben It looks like you have already done most of that.