325 eta surging idle (I've done a smoke test)

[Saeulf]

I have had a fluctuating high idle for a couple months now. It wasn't that bad after I changed the o2 sensor. It mainly just idled around 1100 with an occasional bouncing. The other day I tried cleaning the ICV out real good and that made the surging idle more pronounced (constantly bounces between 900 and 1500 when warm). When I unplug the ICV, the idle goes even higher.

Of course, I thought of vacuum leaks, but the shop I took it to said the smoke test yielded nothing.

So, my question is, what are the chances of my ICM being the culprit? Are there other things I should be looking into?

EDIT: 1986 325

[long tall eta]

have you tried useing another icv? it could be a combination of your icv, maf, tps. our cars are old and these idle things drive us all a little nuts. mine was the combination of all i mentioned.

[jlevie]

The first item in what follows has been done (assuming the smoke test was done properly). Now work through the other possibilities.


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. Hearing a click doesn't mean the TPS is working. Check
with a meter or test light.

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 and/or idle poroblems.

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.

In many cases the cause of problems will be a combination of factors. So it is
important to test and repair all of the possible causes.

[MoreMayhem]

Wow Jim, that is a great write-up on intake problems!

I'm commenting here so I can find it easily by searching for threads I've posted in.

[Saeulf]

What I am most curious about is why a freshly cleaned ICV would amplify the problem? The high idle wasn't bad until I cleaned it thinking I was doing the car a favor... perhaps the ICM is bad and now it has more data to misinterpret? I will attempt to get another ICV to try. Is there an easy way to tell if it is working correctly?

What exactly would a bad ICM do?

Thanks for the grocery list, jlevie :p
I was slowly working thru some of that stuff when I stumbled upon my current question.

[mr.vang]

what i had notice about m20 is that the tps is on the bottom so any juice you throw in through the intake end will drip down to the tps, messing it up.

[bddog]

Idle Control Valve. Drill a quarter inch hole in a penny. Pull the hose on the AFM side of the ICV. Put the penny there and replace the hose. Your idle should even out to about 600RPM. This is a temporary fix until you buy a new ICV.

[Saeulf]

Thanks for the input, all.

Currently, I am awaiting a throttle body gasket so I can do a thorough cleaning. I noticed the TPS is soaked in oil, so I think it wise to take the opportunity to clean it out.

I haven't rulled out the ICV, yet. I want to say it works, because the idle gets worse with it unplugged, but we'll see...

[crazyman]

When you clean the ICV's it is possible to get it to clean if that makes sense, which would cause the hunting to be worse. I bypassed the whole ICV system and left the ICV hooked up. That way I could have it idle without adjusting the throttle plate and throwing the tps sensor all to hell.

[ak-]

Or you can just permanently fix the ICV

http://www.socale30.com/theforum/viewtopic.php?f=1&t=6029

[crazyman]

^um it says it only works on i cars right at the beginning not eta, so no help buddy^

[ak-]

^um it says it only works on i cars right at the beginning not eta, so no help buddy^

Didn't realize it was for an eta my mistake, pal.

[Saeulf]

When you clean the ICV's it is possible to get it to clean if that makes sense, which would cause the hunting to be worse. I bypassed the whole ICV system and left the ICV hooked up. That way I could have it idle without adjusting the throttle plate and throwing the tps sensor all to hell.

What do you mean by 'too clean'? I sprayed it with plenty of carb cleaner and lots of brown gunk came out.

[crazyman]

Yeah it utilizes some of the gunk as restriction to keep the parts from moving to freely. Let me see if I can find that wright up.

[Saeulf]

Oh, I think I see. Basically, the ICV becomes more sensitive, right? I would think that this would indicate an amplification of other issues and signify a properly functioning ICV...