Idles rough, sevice engine light on, EGR valve and solenoid replaced. What is in the vacuum circuit before the EGR solenoid? Auto repair place blocked the line to the solenoid to make it run 50% better.
You have a weak mixture so a fault with the O2 sensors is more likely to be your proble as this is what the codes 171/174 mean and 401 is insufficient gas recycling ,use a multimeter to check the O2 sensors ,so reply if they have three wires or four wires and i will explain how to check them as theyr like 90euros for the 3 wire and 50 euros for the four wire one trade price from a auto factor ,retail?
SOURCE: 97 Eclipse over heating, rough idle, stalls out
Do a cooling system pressure check for a blown head gasket.
SOURCE: Mirage Mitsubishi 2000 1.8L Rough Miss when Idle
Might want to look for vacuum leaks. Most misfires that go away with gas are caused by manifold vacuum leaks. The cat code can also be caused by the vac leak. There are different methods to find them and not real easy-but one way is to get a can of carb cleaner spray and spritz around intake areas. When the carb cleaner finds the leak--the car will run good for just and instant. Could be a rubber line or a manifold gasket. Hope it helped. Thanks
SOURCE: EGR Valve needs cleaning or replacing
The link below is a diagram of the EGR valve. Looks like a mushroom with vacuum lines attached.
http://www.chiltonlibrary.com/content/images/8666/images/86664018.gif
Instructions:
I hope this answers your question. Best of luck.
Greg
SOURCE: EGR CODE P0401,IF I APLLY VACUUM TO THE EGR VAVLE
The mechanical components of the egr themselves may be fine, but the electrical circuit that moves the egr may be faulty. now if the egr valve uses vaccum to operate, then it may be sticking just enough to throw a code.
SOURCE: how to clean/check the egr valve
When the EGR VALVE is
clogged or malfunctioning, it can cause irregularities in engine
performance such as rough idling or valve
knock, indicating that the EGR
valve should be
inspected.
The EGR valve works by routing a
small amount of exhaust back into the combustion chamber. When the
temperature in the combustion chamber is too high, nitrogen oxides
are produced, which combine with elements in the atmosphere to form smog. Introducing a
small amount of exhaust into the system reduces the temperature in the
combustion chamber, reducing the amount of nitrogen oxides produced.
Many EGR valves are
mechanical, and simply have a small valve
which opens to allow exhaust into the combustion chamber and closes
when it is not necessary, and to keep the air mixture optimal for
combustion. Some mechanical versions will not open until there is
sufficient back pressure, ensuring that the valve
will not be open when the engine is idle or warming up and needs a
higher concentration of oxigen for
combustion. Electronic EGR
valves are also available, and use electronics to regulate the valve.
If the EGR valve is stuck open, it
will essentially cause a vacuum leak, leading to inefficient
combustion, rough idling, hesitation, and sometimes stalling in extreme
cases. This is because the car cannot combust on carbon dioxide
from the tailpipe — it needs atmospheric oxygen. If the combustion
chamber is flooded with exhaust from an open EGR
valve, it will not
function properly. To check
and see if the EGR valve is stuck open,
have someone idle a parked vehicle with the brake on while you examine
the plunger shaft to see if it is stuck open.
If the EGR valve is stuck closed, emissions of
nitrogen oxides will rise, and the car may start to knock. Spark knock
happens when the fuel mixture in the combustion chamber ignites before
it has been reached by the explosion in the cylinder, resulting in a
disruption of the engine timing. In this instance, the engine should be
warmed up and revved to see if the EGR
valve will move.
In both cases, simple repairs are possible. The EGR valve can be clogged,
and a simple cleaning of a mechanical EGR
valve may solve the
problem. In the case of an electrically controlled EGR valve or a more complex
mechanical problem, replacement of the valve
may be needed. The EGR
valve is an expensive
motor vehicle component, and care should be taken to ensure that it
needs to be replaced rather than repaired. A reputable mechanic should
advise you appropriately.
Failure to repair or replace the EGR
valve will not lead to a
life threatening condition, although it will reduce the life of your
car and increase the potential emissions. Especially in areas which
require smog testing, an automobile with a malfunctioning EGR valve may not pass
HERE can find one video about this subject.
Hope help with this (remember rated this help) Good luck.
EGR Vacuum Regulator Solenoid
The EGR vacuum regulator solenoid (Figure 88) is an electromagnetic device which is used to regulate the vacuum supply to the EGR valve. The solenoid contains a coil which magnetically controls the position of a disc to regulate the vacuum. As the duty cycle to the coil increases, the vacuum signal passed through the solenoid to the EGR valve also increases. Vacuum not directed to the EGR valve is vented through the solenoid vent to atmosphere. Note that at 0% duty cycle (no electrical signal applied), the EGR vacuum regulator solenoid allows some vacuum to pass, but not enough to open the EGR valve. 
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Codes are P0174, P0171, P0401
Were are the O2 sensors located? Intake, exhaust? How do you use a multimeter to check them?
the O2 sensors are in the exhaust pipe one before the cat and one after depending on country its sold in as some only have one ,what you do is to disconnect the multilpug ,then assuming its a 4 wire then their are two wires the sma e colour possibly white ,check for a 12v feed from engine loom with ignition on ,then the other loose end from the sensor check for continuety across the same two wires ,now the other two you push a pin through and connect the plug then start engine and you should read a voltage across these two that varies with RPM ,different vehicles can show a different voltage but if i remember rightly then its somewhere around the 5 volts up and down a bit .Right star trek is about to start so .Three wire is the same but the third wire you put the other probe to earth .right theme music starting
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