Help!! I'm going to get hit by a semi truck!! Random stalling, stumbling idle

[TomsSVX]

drop the pipes off the manifolds to see if there is a massive restriction in the exhaust.

Tom

[macadamianut]

Thanks again to all who are still with me, I'm really trying and learning a ton in the process.

Using the manifold intake tube for the IRIS, I did a check for manifold vacuum pressure last night. It measured 50 cm or 19.86 in at 550 rpm idle, only fluctuating about 0.5 cm. Moved a bit as throttle was opened/closed, but did not drop lower than 49 cm at steady rpm of about 2000 rpm. Is this the correct range? Trying to rule out a vacuum leak.

I read another thread about FPR's going bad and sucking gas into the back of the manifold. Will try that test too today.

The worst part (or best) is that I got a CEL code 23. So back to the dealer who installed the new MAF that is about 2,000 miles old.

I also unplugged the knock sensors and ran the car. No change in running condition. Could this indicate that they are not working but not throwing a code?

Also, there is a black connector that sits next to the LH O2 sensor connection. There is nothing connected to it? What is this connector for?

Tom, sorry I have not had time yet to get the exhaust off the manifolds yet. It's pretty rusty down there.

[TomsSVX]

That is a very low vac. for a 2krpm idle... You should be around 22-23"hg and around 21-22"hg at idle...20 at a low is OK

Knock sensors will not make a very noticable difference in their absence

23 still bothers me...

That extra connector is for the variable asssist rack which the LS and L models did not have

Tom

[sowise]

Mac,

I found this site which gives pretty good info on vacuum tests and ideas of how the gauge reacts to indicate other faults. Worth a look atleast might help.
http://www.imperialclub.com/Repair/F...auge/index.htm

[macadamianut]

Sorry its been awhile, I've been down with the sickness ... well, bronchitis anyway.

I cleaned up the OE plugs and re-installed, same soggy bottom, same rough idle.

I grabbed some new toys. A fuel pressure gauge and a proper vacuum gauge.

Here are the results for vacuum tested at manifold entry from surge tank, also tested from top of throttle body:

-19 in. steady @ warm low idle (600rpm)
-21 in. steady @ fast idle (about 1500rpm)
-No needle fluctuations at any time other than when opening/closing the throttle.
-Whacking open throttle nets a drop to 5-6 in. and rebounds to about 22+ in. before settling back to 19 in. @ idle.

While doing this test I noticed that the IRIS valve only opened at quick throttle applications (gave it the berries) and would not open if I very slowly increased rpm. Is this normal, or do I have something backwards somewhere? It did not seem to follow what has been said about opening/closing at particular rpm.

Results for Fuel Pressure:

-No noticeable needle fluctuations
-28-29 psi @ warm low idle (600rpm)
-38 psi max. when throttle is whacked open
-24 psi @ engine shut-off
-26 psi @ 10 seconds after shut-off
-28 psi @ 20 seconds
-34 psi @ 2 minutes
-33 psi @ 20 minutes
-20 psi @ 1.5 hours

Have I found more things that AREN'T wrong??

Thanks,
Mac

[Trevor]

The induction control valve (IRIS valve), is controlled by means of a solenoid valve operated via the ECU, but power to move the valve depends on manifold pressure, which is applied to a diaphragm via the solenoid valve. Therefore it would appear logical that any sudden alteration in manifold pressure could result in an intermittent movement of the valve, regardless of the control signal.

N.B. The overall operation is controlled by the ECU operating the solenoid pilot valve on the basis of both engine speed and the amount of fuel injected, and is not simply confined to engine RPM. The valve can remain closed up until 3,600 RPM and open thereafter, depending on the two combined parameters.

[SoCal LS-L]

Originally Posted by Trevor

The induction control valve (IRIS valve), is controlled by means of a solenoid valve operated via the ECU, but power to move the valve depends on manifold pressure, which is applied to a diaphragm via the solenoid valve. Therefore it would appear logical that any sudden alteration in manifold pressure could result in an intermittent movement of the valve, regardless of the control signal.

Also the condition of the diaphragm can cause it to not actuate fully, or hold steady while vacuum is applied. However I do not think the IRIS system could possibly be part of your problem.

It would be helpful to cut and paste a summary of the symptoms and what you have tested and replaced so far, this thread is 81 posts long now and my memory does not serve me as well as it once did.

[oab_au]

Originally Posted by Trevor

The induction control valve (IRIS valve), is controlled by means of a solenoid valve operated via the ECU, but power to move the valve depends on manifold pressure, which is applied to a diaphragm via the solenoid valve. Therefore it would appear logical that any sudden alteration in manifold pressure could result in an intermittent movement of the valve, regardless of the control signal.

N.B. The overall operation is controlled by the TCU operating the solenoid pilot valve on the basis of both engine speed and the amount of fuel injected, and is not simply confined to engine RPM. The valve can remain closed up until 3,600 RPM and open thereafter, depending on the two combined parameters.

The IRIS has nothing to do with the TCU or the amount of fuel injected. It responds to rpm only.

Harvey.

[SoCal LS-L]

Originally Posted by oab_au

The IRIS has nothing to do with the TCU or the amount of fuel injected. It responds to rpm only.

Harvey.

5..4..3..2...1....

[Trevor]

Originally Posted by oab_au

The IRIS has nothing to do with the TCU or the amount of fuel injected. It responds to rpm only.

Harvey.

I sincerely apologise to members for the typo in the second added paragraph within my last post, where it is surely obvious, in view of the earlier text, that I transposed ECU with TCU. This I have hastened to correct.

The IRIS has everything to do with the ECU and the amount of fuel injected and most certainly does not “respond to RPM only.”

The Subaru official manuals clearly states the truth. Ref. 2-7-4-2 ---

“The intake manifold pressure is controlled by opening closing the induction solenoid valve, which is determined by the ECU, according to the engine speed and fuel injection quantity.”

I have entered this in my records as correction number H - 24.

[TomsSVX]

Either way... it would never create this kind of an issue unless it broke apart and ended up in the valves. SO.... moving on

Tom

[oab_au]

Originally Posted by TomsSVX

Either way... it would never create this kind of an issue unless it broke apart and ended up in the valves. SO.... moving on

Tom

Yes Sir.

Harvey.

[Trevor]

Originally Posted by TomsSVX

Either way... it would never create this kind of an issue unless it broke apart and ended up in the valves. SO.... moving on

Tom

Yes, so we can move on, now that incorrect information does nor remain permanently recorded.

But "either way" --- A leaking diaphragm or connection involving the IRIS actuator, could forseeably cause “this kind of issue”, i.e. Random stalling, stumbling idle. It is noted that the possibility of a manifold leak has been raised more than once. Furthermore it appears that the vacuum tests carried out via the IRIS intake tube, were suspect.

This advice also requires further investigation.--- #64, “Still wondering why the car is blowing air out at the connection between the MAF and airbox lid??”

A process of logical analysis must result in an answer.

N.B. #82 Chris --- It would be helpful to cut and paste a summary of the symptoms and what you have tested and replaced so far, this thread is 81 posts long now and my memory does not serve me as well as it once did.

I would go further and call for a tabulated concisely abbreviated summary. Help is on hand, but should be properly directed.

[SoCal LS-L]

Just for fun, remove the EGR temp sensor (or bolt) that resides in the top of the EGR piping into the manifold and observe the behavior of the exhaust being piped through it while you rev the engine slightly.

The backfiring up through the intake is a good clue to follow, theres only a few things that can cause it.... like a restricted exhaust, bad cam timing, bad ignition timing (you checked? PITA on our cars, but very unlikely to be off), and leaky injectors (doubtful from your pressure readings.)

For some reason there is combustion while the intake valves are still open, OR one or more does not close fully. Or even quite possibly extremely high exhaust backpressure is keeping the cylinders pressurized all the way thru the cycle and being released back into the intake when those valves open. One trick you may try is to unbolt both O2's and start it up.... it will be LOUD but if it idles better then you know something is restricting the exhaust, probably the cats.

[oab_au]

Chris, Mac says that the engine clears up and runs fine over 4000. So that rules out a lot of things like a blocked exhaust, and a lot of mechanical troubles.
It really seems to me to be a spark timing or mixture problem, caused by, air leaks, fuel delivery??????

Harvey.