Request assistance with troubleshooting the following issue... Perhaps have narrowed down to bad ECU (DME) but request assessment from E30 community.
1988 E30 320i with Motronic 1.3 ECU.
Low idle problem started 2 months ago. Car just stalled all of a sudden one day at a stop light, and will stall for low idle if throttle not held open. (Car running fine prior to that.) Have overcome problem temporarily for now by adjusting throttle valve open slightly with throttle stop screw - increasing idle RPM to 750ish and preventing stall when stopped. Car seems to run reasonably well otherwise (*minus possibly-related caveat below*).
Have thoroughly cleaned ICV and the valve seems to rotate smoothly back and forth using twisting-shake method. Have "ohmed-out" the ICV and it seems to be in order, approximately 40 and 20 ohms respectively across appropriate terminals. Verified power to the wiring harness ICV connector center terminal is 12Vplus and ICV buzzes normally when plugged in and ignition turned on.
Have tested electrical connections from ECU (DME) plug (terminals 4 and 22) to ICV - both continuity from ECU (DME) connector out to wiring harness ICV connector, AND from ECU connector terminal 4 out THROUGH the ICV (when plugged in) and back to terminal 22 (40 ohms). All seems good.
However... my ECU appears to always have error code 1262 - "Idle Speed Actuator." The info I have regarding that code is...
1262 - Possible causes for Idle Speed Control fault are:
Ӣdamaged wiring to the idle speed actuator
Ӣwire from DME is defective
Ӣoutput stage of DME is damaged
Also if engine stalls while it is above 600 RPM, code 1262 will be set
As indicated, I've checked the wiring between the ECU and ICV as thoroughly as I can, and it all seems good. Regarding the other two dot-points...
- I wonder what "wire from DME is defective" might mean? The output of DME is just male terminals on a connector on the side of the ECU (DME) box. No "wires" coming out of the DME. Could this mean INTERNAL wiring within the DME?
- I understand that "output stage of DME" refers to the DME's internal connections to ground (through the case and out through the grounded bracket), and that the DME uses these ground connections for most all its control functions. Currently, most all DME functions appear to be working normally (injection, ignition, sensors, etc) so it seems as if the grounds within the DME are good. (Would the idle control function within the DME have its own specific ground?)
Note that when I pull off the connector to the ICV, there is no change to the idle RPM - just stays where it's at. (And the throttle position sensor is definitely "clicking" just prior to getting to zero throttle and the wiring between throttle pos sensor and ECU/DME tested good, so DME should be sensing idle throttle position and controlling ICV accordingly.)
Anyway, before I haul-off and purchase a new/pre-loved DME, I'd like to be confident that that is the problem. (Unfortunately, there are no other E30 folks in the local area from which to borrow an ECU for swap checking.)
***The caveat... Lastly, ever since the above idle issue started, and even with the temporary fix with the throttle stop screw, my car occasionally (once per day?) simply stalls. Always at a stop or very slow speed. Starts right back up and then works fine. No DME codes other than the 1262 mentioned above. Suspect the main idle issue and the occasional stall issue are perhaps somewhat related.
Anyway, request thought from the experienced E30 community.
1988 E30 320i – Idle problem and ECU Code 1262
Moderator: martauto
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jimbom30cab
- Tech 1 freak
- Posts: 7634
- Joined: Mon Oct 12, 2009 11:00 pm
- Location: in the garage
Just wondering if you have tried a compression test. I know someone who had the very same problem, low idle and stalling, it turned out his engine was simply well worn and new piston rings were needed.
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jimbom30cab
- Tech 1 freak
- Posts: 7634
- Joined: Mon Oct 12, 2009 11:00 pm
- Location: in the garage
I also found this on the net a while back which i keep in case of idle problems:
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.
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.
I believe I misspoke in my original post... It looks as if really, the grounds of my version 1.3 ECU (DME) seems to come out via at least pins 2, 14, 19, and 24. And... if I'm reading the Electronic Troubleshooting Manual (ETM) diagram correctly, it also seems as if all of them should end up at ground G103. Also, on the 2 pages that shows the idle control valve and ECU together, it only shows pin 19 to ground (going through S700, wherever that is!). So I'm going to presume that pin 19 is the key one that provides ground to control the Idle Control Valve (listed as "Idle Speed Actuator" on the diagram). Not sure how I got the idea that all ECU grounds were through the ECU box's chassis! Anyway, given the reading I've been doing tonight, I will go check and refurbish the G103 ground in the morning and see how that goes. (Lots of other little things that I think need that ground point have been a bit dodgy as well.