2004 8.1 liter Volvo does not always start first try at idle

[Perfect Storm]

I have a 2004 8.1 liter Volvo that will sometimes will fire up and then immediately die on startup at idle (hot or cold). This condition is sporadic. When this happens I need to crack the throttle slightly to get it to start. When it does start the tach only jumps to about 900 rpm then drops to about 3-400 rpm and finally settles in at around 600. When it doesn't start the tach will jump to about 900 and then die.

Have done the following to the engine:

Replaced idle air control motor AC Delco brand (helped a little)
Cleaned throttle plates and body
Replaced plugs that had 300 hours
Tested high and low fuel pressures. -Good
Tested for vacuum leaks - none

Once started boat runs perfect - no signs of rich or lean conditions
Any suggestions

Engine:
8.1 GI D
3869224
4012096668

 

[alldodge]

Tested high and low fuel pressures. -Good

Howdy

What does good mean?

 

[Perfect Storm]

46 psi on the high side
11 psi on the low side

Pressures were constant from idle to 3000 rpm

 

[alldodge]

If the fuel pressure stays steady during start up, then issue eludes me. If the pressure drops during start up then maybe the something is causing fuel to drain back.

 

[Perfect Storm]

Fuel pressure remains constant during start up, I left the gauge on the high pressure side for 15 minutes after shut down and pressure did not drop.

 

[alldodge]

With it being random as you know its going to be hard to find. Its a bad connection somewhere, and would start with grounds, relay contacts, engine harness plug or even the key switch

 

[Perfect Storm]

Thanks, I will let you know when I find the problem, If anyone else has experience with this, please jump in.

 

[Perfect Storm]

Update
I have since purchased a Diacom diagnostics software kit. Way cool, but still unable determine issue. Here are the results. If anyone can see something that I am missing please join in. 8.1 Volvo still needs a little throttle to start:

Boat was warmed up at time of snapshot. Elevation was at 5900 ft.

Engine Cooling Temp. 154.4 (78.1 at cold start up)

Manifold Air Temp. 85.6 ( 79.2 at cold start up)

Baro from map. 24.0 inHg (6000 ft elevation)

Manifold Absolute Press. 11.6 inHg. (23.2 at WOT)

Injector pulse width. 2.4ms. (6.9 at WOT)

IAC Position. 138. ( 96 at WOT)

IAC Follower. 9.0. ( 63 at WOT)

Throttle Position. 6.6 %. ( 99.6 at WOT). Smooth transition through entire throttle range

TPS Voltage. .75 v. (4.4 at WOT)

Closed throttle. Off

Spark Advance. 5.4 degrees. (26.9 at WOT). This seems alittle low to me. At idle it averages around -2 to +2

Knock retard. Always at zero

Cam retard. 67.07. (67.78 at WOT)

Octane rating adap. 99.6%

Trouble codes. None

 

[alldodge]

still needs a little throttle to start

IAC Position. 138.

Throttle should not be needed to start, IAC position, counts should be 0-40, being 138 is high, but your also a mile high. Check wiring connections between IAC and ECM.

 

[Perfect Storm]

Put an ohm meter on all 4 wires to the IAC and got full continuity. Also put a test light on all 4 wires with the engine running and they all lit up. One other symptom that tells me you are probably correct on the IAC diagnosis is when I give a quick throttle and release the motor will die about half the time. I am thinking the brand new AC Delco valve may be defective. I was not sure on the IAC values so that helps. Any ther thoughts? Thanks

 

[alldodge]

In most cases a new IAC will not be bad, and changing from old one to new only help a little if that, right?
Check the air passage for the IAC and see if its partially clogged. Make sure the plunger can move freely

 

[Perfect Storm]

Idle air passages appear to be clear and plunger on iac moves freely.

Other notes.
Idle speed does not change with iac disconnected.

Also, if I remove the iac and move the plunger and then reinstall it operates within specs until I rev the engine and release the throttle. At this point it stays up in the 90's and will not settle back down where it should be. One other question while you have been so generous to respond. Will a high IAC position cause a loss in power around the 3000 rpm range.

Thanks

 

[alldodge]

Idle air passages appear to be clear and plunger on iac moves freely.

Other notes.
Idle speed does not change with iac disconnected.

This makes me think you have a vacuum leak or with comment below, the throttle linkage or throttle plate is sticking.

Also, if I remove the iac and move the plunger and then reinstall it operates within specs until I rev the engine and release the throttle. At this point it stays up in the 90's and will not settle back down where it should be.

Will a high IAC position cause a loss in power around the 3000 rpm range.

In most cases NO, reason being is that once the motor is above 1500 or so rpms, the IAC has no effect. Then the MAP and TPS take over and the additional amount of air the IAC is providing is minimal

 

[Perfect Storm]

Sorry so long on response, have checked throttle plates and linkage, they are working smoothly. Have double checked for vacuum leaks and found none.

Note, this condition is intermittent. I would assume a vacuum leak would be consistent.
Just for kicks I tried a third IAC which did not resolve the issue. I am assuming that when it stalls when punching and releasing the throttle it is starving for air at an idle. Am I correct on this assumption?

Also, I have run some diagnostic graphs on all of the sensors and ecm functions (when the stall occurs) and pasted them in a Word document. Is there any way to post these so you could look at them? Thanks again for your help

 

[alldodge]

Is there any way to post these so you could look at them?

Either convert to PDF or if you have power point it can be saved as a jpeg