Correcting Poor Idle Control (Editing current info for clarity)

[Whitfield]

By Ian L.   Revised in second post, Hope to compare and clean up into one post very soon.  I need more time then I can dedicate to it right now.

According to the Suzuki FSM for Japanese-built vehicles, thermo-wax devices are used in auto-choke carburettor, single point FI and multipoint FI designs.  Both the FI models use an Idle Air Control Valve, controlled by the ECU (on single point / TBI Throttle Body Injection, it's called the Idle Speed Control Solenoid Valve).  I believe that the valve does not have sufficient range of control to manage cold engine conditions, which is why the thermo-wax device is needed.

My multipoint FI suffers from a condition where the idle revs go low during warm up, too soon.  The wax pellet expands too quickly, and cuts off the supply of extra air before things are warm enough not to need it.  My fix is to rotate the air-adjust screw to give more air in all conditions.  When warm, the IAC valve still controls the idle to the factory value, so it overcomes the problem the extra air would otherwise create.  The screw is normally set to give "50% duty" reading on the IAC Valve; I think mine is nearer 80% off/ 20% on.  If you adjust too far, you run out of control range of the IAC Valve, and the idle revs (hot engine) will be too high.

On single point, the ISC Solenoid Valve is also supposed to be operated at 50% duty, set by the air-adjust screw, so I think my fix would work there too.  However, the North American-built trucks may use thermo-wax devices from a different manufacturer, with different problem(s) 


Air Adjust screw for TBI / Single point   look on the Throttle Body, just below the fuel line and maybe an inch to the left of the Fuel Pressure Regulator - it looks like a crosshead screw into the TB.


The 8v (Single Point / TBI) uses a throttle opener device to open the throttle extra during starting.  When the engine starts to run, a vacuum line is applied to the device through a vacuum servo valve, controlled by the ECM.  The vacuum closes the throttle opener, to bring the revs down to normal.  The ECM will operate the VSV after about 10 sec from engine start (less if the coolant is warm).


Throttle opener (1.6L 8v TBI/SPI)   The Throttle Opener pushes the throttle open a set amount to create fast idle using a Vacuum Switching Valve.  Once fast idle is complete the computer switches vacuum to the throttle opener to close the fast idle back to curb idle warm.

Pull the vacuum line off the VSV and the throttle opener should engage, pushing the RPMs up as expected.  Repeate this step several times to see if there was any "restriction" to movement in the throttle opener itself.   

One way of checking whether the throttle opener is your problem is to put a spare bit of pipe onto the throttle opener vacuum inlet and see if you can "suck the revs down".  If you can, the throttle opener vacumm supply is the problem. 

Two common problems with the throttle opener are:

1. The VSV has a defect - read Reply #6 on this thread http://bbs.zuwharrie.com/content?topic=25019.msg257431#msg257431

2.  The vacuum line gets blocked or leaks.


Throttle Opener VSV
    The Throttle Opener VSV solenoid should measure 33 to 39 ohm.  With electrical connector removed, and the hoses disconnected from the throttle opener and intake manifold, it should be possible to blow into the top hose and air should come out of the bottom one, but not out of the filter on the top.  Then apply 12 Volts to the socket (+12V to the LH terminal) and air should come out of the filter but not the bottom hose.  If any of these tests fail, replace the VSV.
(1.6L 8v TBI/SPI) Throttle Opener VSV is coded Brown, controlled by B14 on ECU thru wire coloured Lg/W.  EGR VSV is coded Blue, controlled by B5 on ECU thru wire coloured Lg/Y.


Checking a VSV (Vacuum switching valve)
  With a vacuum gauge connect to teh input of the VSV.  Plug the opposing end.  Pull vacuum, vacuum gauge will climb then slowly fall.  Then apply 12V to the connector.  Now applied vacuum should not raise gauge.  Gauge may move slightly but not raise hold & fall.   If vacuum gauge raises and falls check filter on top of VSV or replace VSV.


Checking  the IAC (it's called the ISC on Single Point TBI)
It is screwed to the throttle body, and has a 2 pin electrical connector) with an Ohmmeter - the solenoid should be 11 to 14 ohm.  If not, replace. 

To test the IAC / ISC
Use a Duty Meter, and adjust the air adjust screw to get 50%.  If the revs are not right at that point, adjust some more to try to get them correct, but if the duty goes below 28%, a vacuum leak is highly likely.


Wiring Harness / ECU / PCM
the FSM says if the idle speed is too high, and the ISC Valve Solenoid resistance is correct (11 to 14 ohm), and the duty is not less than 28% (or more than 72% if it's OFF Duty measurement), then it's either the Lg/B wire is shorted to ground or the ECU has a defect.

So unplug the ECU and unplug the connector to the ISC Valve; then check for ground on the Lg/B wire at the ISC connector.  If there's no ground fault, try a known good ECU (not the easiest thing to get hold of, I know).

Come to think of it, if the timing is all over the place with C connected to D, that's an indication that the ECU is haywire, because the timing corrections from the ECU should be disabled in that condition.

For more on Bad (Computer ECM / PCU) please see post  http://bbs.zuwharrie.com/content/topic,22273.msg226852.html#msg226852  list in the FAQ.

[Whitfield]

Improved version....   But, Still needs some pictures 

We still need a pic of the SPI air adjust screw.

All 8v 1.6L's are SPI and all 16v are MPI


Idle revs go too low, too soon, during warm up.  (Vehicle stalls at the lights, etc)

Thermo-wax devices are used in Single Point Fuel Injection (SPI) / Throttle Body Injection (TBI) and Multipoint FI (MPI) designs, to control an “extra air” passage, which bypasses the throttle.  The purpose of this is to raise the idling revs whilst the engine is cold.  This is important to ensure sufficient lubrication and to warm the engine quickly, to minimize wear. Both the FI models use an Idle Air Control Valve, controlled by the ECU (on SPI / TBI, it's called the Idle Speed Control Solenoid Valve).  I believe that the valve does not have sufficient range of control to manage cold engine conditions, which is why the thermo-wax device is needed.

My MPI suffers from a condition where the idle revs go low during warm up, too soon.  The wax pellet expands too quickly, and cuts off the supply of extra air before things are warm enough not to need it.  My fix is to rotate the air-adjust screw to give more air in all conditions.  When warm, the IAC valve still controls the idle to the factory value (800 rpm), so it overcomes the problem the extra air would otherwise create.  The screw is normally set to give "50% duty" reading on the IAC Valve; I think mine is nearer 70% off/ 30% on.  If you adjust too far, you run out of control range of the IAC Valve, and the idle revs (hot engine) will be too high.

On SPI/TBI, the ISC Solenoid Valve is also supposed to be operated at 50% duty, set by the air-adjust screw, so I think my fix would work there too, and others have said it does.

It would be nice to be able to just replace the wax pellet with a new one, which would work as designed, but it seems not to be available as a spare.

There are suggestions around to remove the wax pellet and block the air passage with a tube closed at the other end.  Doing this removes the elevated idle revs during warm up, and will guarantee excessive engine wear.  I’ve seen it suggested (as a plus) that it’s a good thing to do to save fuel – not at the cost of worn bearings and bores, it isn’t!

Air Adjust screw for SPI/TBI    Look on the Throttle Body, just below the fuel line and maybe an inch to the left of the Fuel Pressure Regulator - it looks like a crosshead screw into the TB.

Air Adjust screw for MPI   Look at the top of the rear edge of the Throttle Body, for a screw set into a small tubular orifice (should have a neoprene bung covering the screw)  Grab Wildweasel’s pic http://home.comcast.net/~icepoint/P1010014.jpg

Idle revs run too high, after warmup


Throttle opener (1.6L 8v SPI/TBI)   The 8v (SPI / TBI) uses a throttle opener device to open the throttle extra during starting.  When the engine starts to run, a vacuum line is applied to the device through a vacuum servo valve, controlled by the ECM.  The vacuum closes the throttle opener, to bring the revs down to normal.  The ECM will operate the VSV after about 10 sec from engine start (less if the coolant is warm).

When it’s operating as it should, you can pull the vacuum line off the VSV and the throttle opener should engage, pushing the RPMs up as expected.  Repeat this step several times to see if there was any "restriction" to movement in the throttle opener itself.   

One way of checking whether the throttle opener is causing the high revs problem is to put a spare bit of pipe onto the throttle opener vacuum inlet and see if you can "suck the revs down".  If you can, the throttle opener vacuum supply is the problem. 

Two common problems with the throttle opener are:

1. The VSV has a defect - see below

2.  The vacuum line gets blocked or leaks.


Throttle Opener VSV

To identify the Throttle Opener VSV, it is coded Brown, controlled by B14 on ECU thru wire colored Lg/W. ( EGR VSV is coded Blue, controlled by B5 on ECU thru wire colored Lg/Y.) 

The Throttle Opener VSV solenoid should measure 33 to 39 ohm.  With electrical connector removed, and the hoses disconnected from the throttle opener and intake manifold, it should be possible to blow into the top hose and air should come out of the bottom one, but not out of the filter on the top.  Then apply 12 Volts to the socket (+12V to the LH terminal) and air should come out of the filter but not the bottom hose.  If any of these tests fail, replace the VSV.


If the vehicle is MPI, or problem is not the Throttle Opener (TBI/SPI), it may be caused by an Idle Air Control Valve defect, a wiring harness problem, or a defective ECM.

Checking  the IAC (it's called the ISC on Single Point TBI)

It is screwed to the throttle body, and has a 2 pin electrical connector). Check with an Ohmmeter - the solenoid should be 11 to 14 ohm.  If not, replace. 

To set the IAC / ISC

Find the Monitor Coupler in the harness behind the RHS headlamp.

There are two types of Monitor Coupler (some vehicles have both); see the drawings. http://bbs.zuwharrie.com/content/topic,27886.0.html Reply #2

Ground Diag Switch Terminal to Ground Terminal.  Connect a digital meter with a “duty” (time on vs. time off) facility (or a real analogue voltmeter) between Duty Check Terminal and Ground Terminal.  (I haven’t used the terminal letters here, because they differ between the two types).  The Duty Check Terminal is top left on the 4 pin connector, and bottom
right on the 6 pin

With the engine running at normal temperature, adjust the air adjust screw to get 50% duty, or half battery volts (as measured with engine running).  If the revs are not right at that point, adjust some more to try to get them correct, but if the duty goes below 28%, a vacuum leak is highly likely.

Wiring Harness / ECM
 
The FSM says if the idle speed is too high, and the ISC Valve Solenoid resistance is correct (11 to 14 ohm), and the duty is not less than 28% (or more than 72% if it's OFF Duty measurement), then it's either the Lg/B wire is shorted to ground or the ECM has a defect.

So unplug the ECM and unplug the connector to the ISC Valve; then check for ground on the Lg/B wire at the ISC connector.  If there's no ground fault, try a known good ECU (not the easiest thing to get hold of, I know).

[Whitfield]

Also:  Another item to look at is the EGR Valve. 

Check your EGR, Make sure it is closed and receiving no vacuum signal at idle.

A stuck, broken or improperly plumbed VSV (Vacuum Switching Valve) could feed the EGR causing it to open at idle.