Cold Start Issues

[BMWManiac]

I've searched, but I wanted to get some validation on my thought process.

'91 325i/M20 motor:
-Cold start issue/motor will sometimes stall
-hesitation and bucking when cold
-once warms up, runs like a champ!
-P1222 fault code

Done as soon as problem arised:
-fuel filter
-fuel pump
-02 Sensor
-spark plugs
-CPS

When I pulled the old O2 sensor out, the sensor was definitely white, indicating a lean fuel mixture, which would cause the P1222 fault

So, I'm guessing on a vehicle that is 20 years old, that the fuel pressure regulator is probably going out.

I don't think it is a vacuum leak or else the problem would be consistent. I saw the most significant improvement after changing out the CPS. Since then, the problem ONLY exists at cold start. I used have hesitation at higher RPMs, as if the engine was starving of fuel, but now it revs like it used to.

So, do you think I'm on the right track or could there be something I'm missing.....coolant temp sensor more likely a culprit?

[E30_fiend]

Only other thing I can think of would be fuel injectors. The cts would cause a rich condition or a lambda code. Have you ever pulled the injectors out? My guess is they are leaking and flooding the cylinders when it sits. The reason for running well when its warmed up is because the fuel doesn't have time to leak without being burned.

Just my two cents. But I thought since no one chimed in, I would at least give you my thoughts.


Taylor

[BMWManiac]

Thanks for the insight.

On a separate note, I let the car idle a couple minutes before driving off. Not a single issue, hiccup, even after driving 45 min this morning. I will say that prior to replacing the cps, the car, even after warming up, would act up.

So, I will see if the problem continues or perhaps the dme is continuing to adapt due to the new sensor

[BMWManiac]

So the past couple of days the car has been running like a champ, thought the issue was resolved....

and then this morning was like back to square one. Hesitation, no response to the throttle ,sputtering.....and then after the car warmed up, it was fine.

[jlevie]

Start at the top of what what follows and work towards the bottom.

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.

[BMWManiac]

Without going through any extensive diagnosis, what I think I've realized is that I have a leaking injector....

Whenever I start up the car after it has been sitting overnight, there is an obvious fuel smell. I must be flooding the engine on startup.

Once I get going for a bit, the car runs flawless....

[harold30]

Try cleaning your injectors and replace o-rings, washers and pintle caps.