E30 running rich

[jaydeep]

I have E30 which is running rich. After car is warmed up for 5 min. Check Engine light comes on. It feels like car does not like to idle however rpm gage stays at 800 and does not jump. I pulled Code using PEAKE and got code for 0A which is Emission Control (lambda).
My guess is it could be
1) Oxygen sensor
2) Coolant temp sensor (Brown plug)

What do you guys think?

[jlevie]

It would have been better to ask this in the General Technical, or engine specific (M20, M42, M10) sections.

A Lamba code means that there is a problem (real or perceived) with the A/F ratio. The most common cause is intake leaks, but other causes are possible. On the assumption that this is an M20 engine, work through:


Idle or hard starting problems are most commonly caused by intake leaks and/or
a sticky or defective Idle Control Valve (ICV). The only reliable method of
locating intake leaks is to have a smoke test run on the intake and crank case
and to test the brake booster with a gage and vacuum pump. The complete list
of possible causes of an intake leak is:

Intake boot
Throttle body gasket
ICV hoses & connections
Brake booster, hoses, and connections
Crank case breather hose
Evaporative control hoses, valve, and expansion tank
Fuel pressure regulator & hose
Injector seals
Valve cover gaskets & bungs
Oil filler cap
Dip stick o-rings
Oil return tube o-rings

While leaks in some of those can be found by inspection or by spraying carb
cleaner on suspect areas, not finding leaks that way doesn't eliminate the
possibility. Only a smoke test will really work.

Once the possibility of intake leaks is eliminated, the ICV needs to be
removed and cleaned with carb cleaner until the vane inside moves freely. When
the ignition is switched on you should be able to feel vibration from the
ICV. If no vibration the ICV is bad, there's a problem with its wiring or
connector, there's a problem with the TPS, or the DME (or Idle Control Module
(ICM) on an ETA car) is faulty.

For the DME (or ICM) to control idle, the idle switch in the TPS must work
correctly. The switch should close when the throttle stop is 0.030-0.060" off
the idle stop screw.

The fuel system should be tested via the suite of tests in the Bentley manual
as invalid rail pressure can be a contributor to idle and starting problems. A
simple injector check is to pull the injectors, jumper the fuel relay to run
the pump, and see if the injectors are leaking. You can also point the
injectors into a towel, remove the coil wire, and crank the engine to see if
all of the injectors appear to be spraying in a similar fashion. The best
approach to possible injector problems is to have the injectors cleaned and
flow tested. Since raw fuel can or will be released in these tests, have a
fire extinguisher handy.

While a bad check valve in the high pressure pump can result in longer than
normal cranking, if the fuel system is working as it is supposed to the rail
will reach normal pressure in a few turns of the engine. A weak pump, clogged
filter or leaking FPR in conjunction with a failed check valve can result in
longer cranking.

The O2 sensor can be a contributor to idle problems. The O2 sensor is a
scheduled maintenance item with a useful life of no more than 100k. If the
sensor has that mileage or more (or is of unknown age), replace it.

The AFM can be a contributor. If the vane doesn't move freely or the
resistance track is worn the DME may be receiving invalid data from the
AFM. And if someone has fiddled with the bypass air adjustment the DME may be
unable to stabilize idle. The bypass air adjustment should only be adjusted
per the procedure in the Bentley and with an exhaust gas analyzer. And even
then everything else associated with engine management has to first be
operating properly. If the AFM becomes a suspect, replacement with a good used
unit is the best approach.

Improperly adjusted or malfunctioning valves will affect idle and starting. As
can compression issues from ring or cylinder wear. A valve adjustment is
called for every 15k. A useful diagnostic is to run compression (dry and wet)
and leak down tests on the engine. Aged ignition wires, plugs, distributor
cap, or rotor can cause problems. Insulation does break down with time and
heat. And since the youngest E30 is going on 20 years old, if the ignition
system is original or the plugs are old replacement is indicated.

Although not usually a problem, a bad DME temp sensor is a possibility. That
generally won't cause an unstable idle, but can cause hard cold or hard hot
starts and/or a rough idle. As can problems with the timing reference
sensors. Although not commonly encountered, a bad harmonic balancer on an
M20B25 or M30 engine will cause problems.

When all other possibilities have been eliminated and idle or starting
problems persist, replacement of the DME, or if applicable the ICM, is
indicated.

[AlphaE]

my car had this when i bought it. I checked the fuel pressure it was pegged at like 70psi. Turns out the return line in the tank was plugged. That sucked to get cleaned out. Its a possiblity that somethin of that nature could be the issue too.

[jaydeep]

my car had this when i bought it. I checked the fuel pressure it was pegged at like 70psi. Turns out the return line in the tank was plugged. That sucked to get cleaned out. Its a possiblity that somethin of that nature could be the issue too.

How do I check to see if return line in the tank is plugged? Do I need to take out fuel tank?

[jlevie]

How do I check to see if return line in the tank is plugged? Do I need to take out fuel tank?

Check the rail fuel pressure. If it is too high, re-check with the return hose directed into a container. If the pressure is normal then, there is a blocking in the return line. If it is still the FPR is bad.

[jaydeep]

Check the rail fuel pressure. If it is too high, re-check with the return hose directed into a container. If the pressure is normal then, there is a blocking in the return line. If it is still the FPR is bad.

I am planning to follow this steps.
1) Check Coolant temp. sensor with volt meter
2) Check O2 sensor with volt meter
3) Check fuel pressure with fuel pressure gage
a) Check pressure at intake line where fuel line goes to fuel rail.
b) Check pressure at out line after FPR

Any other suggestion?