Originally there was a code P0300. Also P1345 pending. I replaced a bad EGR gasket, cleaned some corrosion from EGR valve connector pins, and changed the spark plugs. Now I got a misfire code for #2 ... I'll check resistance on that wire tomorrow. The most noticeable problem is the surging at low rpms. It acts like the accelerator was being pedaled even when it's held still. Under load it works fine, although the surging is somewhat noticeable when cruising at highway speeds ... almost like driving into a gusty wind. I noticed the fuel trim numbers fluctuate a lot. Also the O2 sensor readings.
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1.6b) Symptoms of faulty EGR Associated OBD2 error codes DTCs: P0400 - P0409; P1403 - P1409 other common codes can include 'multiple misfire P0300' The EGR has two possible fault modes either it is 1) open when it should be closed or 2) closed when it should be open. (See also DPFE faults) 'Open' faults
Erratic idling:'hunts' at idle with erratic engine performance when running.This is due to the air ingress through the split diaphragm or the EGR valve being left open, either event compromises the intake manifold vacuum and in turn this interferes with the ECU's ability to deliver accurate fuel to air ratio for a given engine speed.
Sudden engine stall:In addition to the rough idle, a hot running engine when quickly brought to idle (after the car comes to a halt at a junction) can stumble and then stall. The engine will hesitantly restart immediately:this is significant difference to Crank and Camsensor error.
Misfire and 'pinking': if the EGR is jammed closed or the exhaust feed pipe is blocked (with baked on carbon deposits) the engine runs lean and very hot, so hot in fact that the fuel air mix in the cylinder can spontaneously ignite causing a misfire.The misfire if pronounced can, in turn, be detected by the engine knock sensors (P0300) leading to a 'check engine light' warning and reduced engine speed limitations.
Inherently diesel engines create more soot in the exhaust and as a result blocked EGR assemblies are more common in diesels than petrol engines.
Burnt Exhaust Valves.Prolonged exposure to excessively high ignition temperatures brought about by a blocked EGR system can lead to exhaust valves being over heated to the extent that they become distorted and so no longer seat properly.Poorly seated valves prevent good compression.
Surging:A sticking EGR valve can lead to an effect of rhythmic surging a bit like the MAF fault, especially in turbo charged engines.Normally on a warmed up engine the vacuum from the inlet manifold opens the EGR.If the EGR fails to open promptly the turbo can be subject to a slight boost.Extra fuel/air mix is pushed into the inlet manifold as a result, increasing pressure (decreasing the vacuum).Without vacuum in the inlet manifold the EGR closes again but if sticky only does so slowly.This may allow inlet gases to flow through the EGR into the exhaust manifold for a split second.There is a time lag in the sequence of these events leading the engine to surge in cyclical manner.
Most of the time, one defect triggers another, and so on, and if the primary problem is fixed, the other defects may clear when given some time.
The easiest of your Codes to fix is the P0401. This is an EGR airflow Code problem in the throat of the airhorn. The passageway which feeds the EGR is dirty. You need to clean the port between the intake and EGR.
Code 1131 is lean reading from O2. Can be restricted fuel injector or low pressure, or too much airflow to cylinders from a leak.
Code 1151 is a Vacuum leak. Can be detected with engine running by spraying water from a spray bottle to seams and lines.
Codes 1233, 1234. Bad connections on wire ends, (Known defect of Factory crimps) At fuelpump, inertia sensor, or fuelpump module.
You need fresh fuel. Fuel injector cleaner could help. The water spray can detect leaky gaskets that are dried up. You could easily have corrosion on connections, especially under the car.
cold engine idle surge. (problem) RPM range of surge not stated 300-700 or 800 to 1500? (range is critical to diagnosis)
bad fuel running summer fuel in winter (running old fuel?) needs a tune up bad, see the list in the operator guide. idle speed controller,sticking or EGR valve same. (clean them) location not stated, so cant guess about local air temps.? no other symptoms, lack of engine power? etc? was it ok last week, or better, when was the last time it was OK? 1week, 1year? surge , causes, on a tuned engine might be: 1: too lean. so lean the ISC can not control idle. rpm low, stalling 2: too rich, flooding, stalling, spark plugs foul (look at them) 3: weak compression in 1 or more cylinders. 4: bad spark. 5: air leaks, in the plenum causing , ISC to lose control. why high RPM?
especially? well that means it fails hot too. and there is a simple tests. for hot surge. is engine fully hot? 180F and holds solid there? say rpm is about 800 and you turn on head lights, heater fan and (not AC) and defrost. the RPM must hold or the ISC is failing. ISC -= idle speed controls. (all EFI has this function)
Misfires can be caused by worn or fouled spark plugs, a weak spark
(weak coil, bad spark plug wire), loss of compression, vacuum leaks,
anything that causes an unusually lean fuel mixture (lean misfire), an
EGR valve that is stuck open, dirty fuel injectors, low fuel pressure,
or even bad fuel.
A Random Misfire code usually indicates a vacuum leak or bad gas.
NOTE: If a misfire in a specific cylinder should lead you to check the spark plug, fuel injector and compression.