2005 F90TLRD Another ISC Issue

[username]

I’ve searched here and all around the World Wide Web trying to figure out my problem.

Quick history
After a long run of about 16 miles when pulling back to neutral the engine was idling at 1800 or so rpm. Killed motor, restart and still high idle. Killed engine and waited about a minute and all was normal on restart.

Next trip out did the same thing after a run of 8 miles. Idle was higher this time to 2800 in neutral. After turning key off for a bit the idle returned to normal until I ran back to fish the river I left from. Same thing happened. Turned key off for a bit and all was normal after restart. Fished a bit and all was normal but I didn’t run anything over 2500-3000 RPM when resetting for drift.

The cause of the high idle is the ISC valve is open beyond normal idle position. I can clearly hear it sucking air.

Visually inspected wires to ISC valve and all looked good. However, I didn’t check continuity. When I eventually did, I found no continuity through the green/black at ISC valve connector. Applied some pressure to that wire and it pulled out the back of the connector. De-pinned that connector and repaired.

Before repairing wire I had read several times here from Rodbolt that a malfunctioning valve can over heat the ECM. I checked temp of ISC valve with engine at operating temp (after replacing stuck tstat found with YDS monitor, I could see the low engine temp of 113) and it topped out at 170 degrees. Also code 37 intake air passage at engine hours when it first happened.

With wires repaired I could not get reliable stationary or active ISC valve test with YDS. When I took ISC valve off housing it was stuck full open.

I bought a new ISC valve. No Joy.....Upon cold start it idles at 1100 for a few seconds and quickly ramps up to 2800 and stays there. I can hear it sucking through the ISC valve.

I checked a few things this morning after clearing my head after a nights sleep.

Cold start with new ISC valve installed

1100 rpm for a few seconds, ramps up to 2500-2800. Clearly sucking air in the ISC valve.

Engine off key on voltage at ISC connector
G/y. 12.47
G/b 8.53
G/r 8.44
Same voltages when tested at green ISC connector wire and engine ground

Engine running
G/y 14.62
G/b 8.65
G/r 8.56

Execute stationary test of ISC and I can hear it doing it’s thing.

Execute ISC valve 100% open in active test. Engine running in neutral at 2800, As it increases in % open the ISC actually closes and eventually kills the engine at 100% open. Obviously activating in reverse.......

Check voltage at ISC connector during ISC valve active test and voltage drops to
G/y drops to 7.5
G/b drops to 7.26
G/r drops to 7.24

Disconnect ISC valve connector and engine will idle at 1100 all day long. Of course I’m not sure what all this means other than the ISC valve appears to be working in reverse.

Since someone will likely ask if I crossed wires when taking the connector apart. I confirmed they are correct.

In YDS all monitored sensors are showing as normal.

I’m leaning towards a bad ECM, but hate to throw parts at it. I don’t know a way to confirm ECM function for this issue.

Thanks for any guidance.

[99yam40]

when you turn the motor off the ISC should toggle back to to100% open for the next start.
do you hear that happening?
can you check to see if it is 100% open?

what about your old ISC, how does that act at key off?

[username]

when you turn the motor off the ISC should toggle back to to100% open for the next start.
do you hear that happening?
can you check to see if it is 100% open?

what about your old ISC, how does that act at key off?

I’ll take it off and see for both new and old and report back.

Thanks

[username]

Both old and new set to some percentage open when shutting down. When I start with both new and old the idle is 1100 and within a few seconds the valve opens further and rpms go to 2800. Upon key off both toggle to something. I can’t actually see the pintle when it’s in place on the intake. Given the rpm is at 1100 for a second when starting I think it’s at reset position for start. Why it opens further is the question. And why when active test is done and moving towards 100% why do the rpm’s come down until stall at 100% open.

[99yam40]

from what I understand, the ISC is suppose to go 100% open at shut down.
once started the idle speed is high, but should drop fairly quickly as the ISC is closed off by the ECU.

I would think it would be kind of hard for the ISC to open farther than 100% to add more air.

do you understand this is a stepping motor, so there is not a set voltage for a position.
the ECU toggles voltages to step the motor in one direction or the other to open and close.
the ECU has no idea if it does what it tells it to, because there is no feed back for position

[username]

from what I understand, the ISC is suppose to go 100% open at shut down.
once started the idle speed is high, but should drop fairly quickly as the ISC is closed off by the ECU.

I would think it would be kind of hard for the ISC to open farther than 100% to add more air.

do you understand this is a stepping motor, so there is not a set voltage for a position.
the ECU toggles voltages to step the motor in one direction or the other to open and close.
the ECU has no idea if it does what it tells it to, because there is no feed back for position

I get it. I know it’s opening further because I can meter the air with my finger over the ISC inlet and feather it down to whatever RPM I want. AND when disconnected it will idle steady at 1100

[username]

What I can’t figure out is the voltage requirements from ECM to ISC. It’s not in the manual and even searching for 4 wire ISC voltage for auto applications gets me now where. But those numbers are suspect to me.

[username]

Best I can tell from searching is a 4 wire ISC should only have voltage on 2 wires. 2 are grounds. I would suspect green and green/black are grounds and green/yellow, green/red are signal. I’m dying here........

[99yam40]

as I said search for stepping motors to see how they work

[rejesterd]

Disconnect ISC valve connector and engine will idle at 1100 all day long

What happens if you run the engine with the ISC disconnected AND you plug up the ISC inlet with your thumb (to block the air intake)? Does it still idle at 1100 rpm?

Can you post a YDIS report from when the engine is idling with the ISC valve connected?

[username]

What happens if you run the engine with the ISC disconnected AND you plug up the ISC inlet with your thumb (to block the air intake)? Does it still idle at 1100 rpm?

Can you post a YDIS report from when the engine is idling with the ISC valve connected?

Can do....stand by

[username]

When running and ISC disconnected if I slowly meter air down at ISC port it drops RPM to 300-400, but I feel like if I keep it there long it will stall. I close it of quickly it will stall.

Just noticed timing is not shown. When I look for a CPS in the diagram I don’;t see one. Must not be monitored by this ECM and what’s in the map is what it is

Also notice no 37 code for intake air passage at 461 hours. I cleared that the others day to see if it would come back.


Save date July 27 2020
ECM No.: 6D88591A00

Diagnosis
Code Item Result Condition
13 Pulser coil Normal
15 Water temp sensor Normal
17 Knock sensor Normal
18 Throttle position sensor Normal
19 Battery voltage Normal
23 Intake temp sensor Normal
28 Shift position switch Normal
29 Intake press sensor Normal
37 Intake air passage Normal
44 Engine stop lanyard switch Off
49 Over cooling Normal

Diagnosis Record
Total hours of operation 467
Code Item Occurred
29 Intake press sensor 209.3
49 Over cooling 294.7

Engine Monitor
Monitor Item Result Unit
Engine speed 2671 r/min
Intake pressure 39.37 kPa
Intake pressure 11.57 inHg
Atmospheric pressure 996.2 hPa
Atmospheric pressure 29.5 inHg
Ignition timing TDC deg
Battery voltage (12-16) 14.3 V
TPS voltage (0.5-4.5) 0.943 V
Throttle valve opening (0-90) 6.1 deg
ISC valve opening 10 %
Fuel injection duration 2.86 ms
Water temperature (below 90) 63.3 °C
Water temperature (below 194) 146 °F
Intake temperature (below 70) 41 °C
Intake temperature (below 158) 105.8 °F
Engine stop lanyard switch OFF
Shift position switch ON
Oil press switch OFF
Dual engine system switch OFF

Data Logger[Engine operating hours according to engine speed]
Engine speed Time[h]
- 1000 r/min 307.5
1000 - 2000 r/min 52.4
2000 - 3000 r/min 23
3000 - 4000 r/min 20.1
4000 - 5000 r/min 34.3
5000 - 6000 r/min 30.1
6000 - 7000 r/min 0
Engine hours 467

Data Logger[Data comparison graph]
Engine speed[r/min] Battery voltage (12-16)[V] TPS voltage (0.5-4.5)[V] Water temperature (below 90)[°C] Intake pressure[kPa] Oil press switch[0:OFF 1:ON]
1300 14.28 0.94 60 31.6 0
1250 14.21 0.94 60 32.1 0
1250 14.58 0.94 60.8 32.1 0
1300 14.94 0.94 60 32.1 0
1250 15.16 0.94 59.3 32.1 0
1250 14.36 0.94 59.3 32.6 0
750 14.79 0.94 41.5 31.1 0
550 14.72 0.94 55.7 31.6 0
1250 14.43 0.94 54.4 32.6 0
1250 14.58 0.94 58.6 31.6 0
2600 14.87 0.94 62.5 39.5 0
2700 14.43 0.94 63.3 39 0
2650 14.58 0.94 63.3 39.5 0

[rejesterd]

When running and ISC disconnected if I slowly meter air down at ISC port it drops RPM to 300-400, but I feel like if I keep it there long it will stall. I close it of quickly it will stall.

Ok that's good. If it didn't drop, then that would mean air is getting drawn in where it shouldn't be.

But yeah, 2 of those wires should show zero volts (and my guess is the same as yours.. the solid green and green/black wires). Since they don't, trace the wires all the way back to the main connector for the ECM. Measure the voltage there. The service manual will tell you which pins are which. It seems this is related to the ISC wiring/connection points, or the ECM itself. If you don't get zero volts for those 2 wires at the ECM, I would guess you need a new one. I've searched a lot on how to diagnose them, and there's really nothing out there as far as I've seen.

Another thing that points to the ECM/ISC wiring being a problem is that it's reporting the ISC is opening 10% while the engine is idling at 2600 rpm. No way that's right.

Good luck.

[username]

Ok that's good. If it didn't drop, then that would mean air is getting drawn in where it shouldn't be.

But yeah, 2 of those wires should show zero volts (and my guess is the same as yours.. the solid green and green/black wires). Since they don't, trace the wires all the way back to the main connector for the ECM. Measure the voltage there. The service manual will tell you which pins are which. It seems this is related to the ISC wiring/connection points, or the ECM itself. If you don't get zero volts for those 2 wires at the ECM, I would guess you need a new one. I've searched a lot on how to diagnose them, and there's really nothing out there as far as I've seen.

Another thing that points to the ECM/ISC wiring being a problem is that it's reporting the ISC is opening 10% while the engine is idling at 2600 rpm. No way that's right.

Good luck.

Thanks for the insight. Just to clear something up as I’ve read here and elsewhere. The ECM does not get feedback for position of ISC. What is seen is the ECM request.

All of the ISC wires are direct outputs from the ECM. I had that loom separated from the harness when I was checking the circuit. I suppose I could back probe the connector at the ECM, but I’m pretty sure the results would be the same.

[rejesterd]

Thanks for the insight. Just to clear something up as I’ve read here and elsewhere. The ECM does not get feedback for position of ISC. What is seen is the ECM request.

Right, I should have said that the ECM is requesting that it open to only 10%, yet the idle is very high. So something isn’t right there.