Oh dear. So we've discovered an issue. After a long drive (enough to heat the engine way the hell up), slowing down (therefore lowering the revs) results in the engine stalling. Most of the time when this happens the oil pressure gage drops just prior to the stall. This issue doesn't happen unless the engine has been running a while and is hot, from that point, any slowing results in a stall. Traffic lights, slowing down in traffic etc. We had to limp home with a foot on accel and brake at the same time to keep revs up! Anyone got any ideas?

 

This could possibly be caused by a bad ignition coil or overheating ignition amplifier.

 

Hi BeckBeck,

Here are a few ideas to add to Xdevo1973's:

First, have you checked the Vehicle Condition Monitor (VCM) for any stored Diagnostic Trouble Codes (DTCs)? If a code is stored that may help narrow down the diagnosis.

Low transmission fluid has been associated with stalling when slowing to a stop or to make a turn. Measuring the level while cold will tell you if there's at least a decent amount of fluid, but it's critical to check it hot, after driving the car at speed for at least 20 minutes or more. Park on a level surface, and with the handbrake set and your foot on the brake pedal, move the gear selector lever through every gear position, pausing in each one for 3 or 4 seconds, then move the lever back to Park. Leave the hand brake set, the transmission in Park and the engine running. Pull the transmission dip stick and wipe it off, then fully insert it again, pull it and read the fluid level. The fluid should be a bright, clear red color and its level should come exactly to, or very close to, the HOT line on the stick. A fluid level that is too low (or too high) can cause lots of issues, including stalling.

If your Coolant Temperature Sensor (CTS) has failed at a resistance indicative of cold coolant, the Engine Control Module (ECM) will continue to apply cold-start fuel enrichment even after the engine is hot, leading to rich running. You can test the CTS with an ohmmeter when the engine is cold and again when hot. The Engine Management System manual has a chart showing what the resistance readings should be at different temps, but a rough test is that they should be dramatically different when the engine is cold and hot.

If the carbon canister purge valve is seized open, it will allow fuel vapors from the canister to enter the intake manifold at inappropriate times, contributing to rough running, stalling and starting problems.

The Idle Air Control Valve tends to clog up with black carbon from the crankcase breathing system, preventing proper flow of the extra air the valve is supposed to supply under certain conditions. If you haven't already cleaned it, you can remove the valve and disconnect the stepper motor and clean all the carbon with a small wire brush. I use a battery terminal brush to clean the ports in the valve body. I think I have a photo album on this - see the link in my signature. If the valve gasket is damaged you can use an RTV silicone sealant, but be sure it's safe for oxygen sensors, as not all sealants are.

Is your air filter clean? Fuel filter? What is the condition of your distributor cap and rotor? Spark plug gaps? Spark plug wires?

Cheers,

Don

 

Thanks bud. A lot of these issues I've already checked, it has a new air filter, trans fluid is full / fresh, though when I turn on the electrics just prior to ignition, the trans light does come on. it turns off when the car is started but could be a clue? I'll go ahead and get into the air idle ctrl when I get a chance to, and will check the cts asap as that soes sound like something worth looking into. will triple check trans too.

 

Clean the intake plumbing and throttle body. If the whole throttle body is too much work, at least clean the carbon off the throttle butterfly, use carburettor cleaner and wipe excess carbon away with a rag, that should improve things if not cure the problem.

Larry

 

Cheers, that'll next on the list. Might get into it tomorrow weather permitting

 

The back (engine side) of the butterfly will have the largest amount of carbon buildup. Hold the throttle open in order to clean it.

 

All the instrument cluster warning lamps should illuminate when you turn the key to the ON position prior to starting the engine, and will extinguish as each system passes its self-tests, so it sounds like your trans light is operating properly, though for future reference you should know that these transmissions do not have internal sensors for fluid level, so the warning lamp will not illuminate due to low fluid. The lamp illuminates to indicate problems with the electronic control system between the Transmission Control Module and Engine Control Module.

Cheers,

Don

 

Thanks Don, they all do however a moment after they all shut off again the trans light alone stays illuminated. As ssid, does turn off before starting though.

 

So... cleaned out the icv, it was really gunked up. Unfortunately now the idle is high when i start it up. About 2000 instead of 1000.. how do i adjust the icv? Something about an allen key ive read? Or have i destroyed the thing

 

Set the throttle plate gap to .002(.05mm). This is the gap between the throttle plate and the wall. To do this right, you should remove the throttle body and clean it with some throttle body cleaner and then set the gap. The throttle body/ plate gets gummed up from the crankcase vent being before the throttle.
After setting the gap, reassemble the throttle body and all parts, clamps, wires, etc.
Warm up car,
ac off,
transmission in park,
turn key off,
Turn key on but don't start car and wait 15 seconds then disconnect connector to iscv.
The iscv is just forward of the throttle body, close to the cruse control bellows.
turn key off,
hook up iscv connector,
turn key on but don't start car...wait 15 seconds,
disconnect iscv connector,
(your winding the iscv closed)
leaving the iscv connector disconnected, start the car.
turn the idle speed air bypass screw on the iscv using a 7\32 inch Allen wrench till the rpm is 550 to 600.
Hook up the iscv connector.
Your done.
If the static idle is not set correctly, the rpms will hunt around. The computer is only supposed to raise the idle from base due to a load, so if the base idle is not set right the computer doesn't know what to do, hence the hunting.

 

In regards to the correct procedure for setting the base idle here it is for future reference which comes courtesy of AJ6 FAULT CODES AND IDLE SETTING / AJ6 Engineering

I suggest those that who are not familiar with it's location locate the air bypass adjustment screw which is very near to the stepper motor (IACV) within the same housing. It's adjusted using the appropriate size allen key. It's also very often loose so first thing to do is unscrew it and wrap some teflon tape around the thread to help keep it in position

[/IMG]

IDLE STEPPER MOTOR SETTING PROCEDURE 3.6 Litre


You will need a 5w 100ohm resistor for this process which is available from any electronics store.



-set TPS to 0.32 volts at closed throttle
-set throttle butterfly to 0.05mm or 0.002"

1. Run engine until fully warm.
2. Switch off and remove connector from coolant sensor.
3. Insert 100 ohm resistor across coolant connector terminals.
4. Switch on ignition and after 10 seconds remove connector from stepper motor (which will now be fully seated and closing off idle orifice).
5. Switch off ignition, remove 100 ohm resistor and reconnect coolant sensor.
6. Start engine and set base idle speed to 600 r.p.m. via air bypass adjustment screw near to stepper motor.
7. Reconnect stepper motor - idle should now stabilize around 700 r.p.m.
8. Your done - enjoy your smoother performing engine!

For those with a proper way of diagnosing emissions:

1. Check idle CO2 - factory setting quoted as 1-2% but we find that most engines idle best with a weak setting around 1% or even slightly less depending on HC emission being stable. This is can be done via the set screw hidden away on top of the MAF

3.2 & 4.0 Litre


-set TPS to 0.6 volts at closed throttle
-set throttle butterfly to 0.05mm or 0.002"

1. Run engine until fully warm.
2. Switch off ignition.
3. After 5 seconds switch on ignition - wait 5 seconds - remove connector from stepper motor.
4. Switch off ignition.
5. Wait 15 seconds then replace connector on stepper motor.
6. Repeat operation sequence 3 - 5 twice - on the last occasion do not reconnect stepper motor.
7. Start engine and set base idle to 550 - 600 r.p.m. via air bypass adjuster.
8. Switch ignition off and reconnect idle stepper motor.
9. Restart engine - idle speed should now stabilise around speed shown below.
10. Your done - enjoy your smoother performing engine!
11. Check idle CO as for 3.6 (if non-cat).

Specified Idle Speeds

Cold in neutral - 800 (Auto)
Hot in neutral - 700 (Auto)
Cold in drive - 650 (Auto)
Hot in drive - 580 (Auto) (3.2L = 650)
Hot in Neutral - 800 (Manual)


Note: Cold idle speeds will be slightly higher at very low temperatures.
If the above procedures do not result in stable idling check that the throttle potentiometer is correctly set. Whilst the ECU will automatically compensate for minor errors within the range of the adaptive memory, a badly adjusted throttle potentiometer can cause spurious drive-ability and idling problems.



- don't forget to reset your trip computer to check future fuel
consumption figures

 

I should also mention that when reinstalling the IACV after cleaning that it's very important not to overtighten it. Doing so with crack the thread on the IACV and destroy it.

Best to do it up finger tight, then just a millimeter or two further with the spanner.

 

Thanks so much! Out of curiosity, should the IC valve usually be in a pintle closed or open position before the car is started? It was open when I took it out, though adjusted slightly either direction as I cleaned it. I had wondered if it was put back in the wrong position.

 

That's a really good question Beck...I think it should be open. I'm sure someone will correct me if I'm mistaken

 

So far I'm reading that it may possibly be closed upon start, I guess I might as well fiddle around if resetting doesn't work until I figure it out / cave and find a new one. Thank god I have tomorrow off work!

 

Hah forget that, I meant open.

 

Alrighty. . So today I get into the throttle body. Can we throw some info over this way please? Does an xj40 have an electric or mechanical throttle body (I.e am I going to ruin the world if I hold the butterfly open to clean)? I'm rather set on avoiding the high idle nightmare post TB cleaning. Is it safe to remove for cleaning or will I end up throwing off the computer if I do? What's the best procedure to avoid issues with the sensor? Cheers guys

 

Hi BeckBeck,

The XJ40 throttle is operated mechanically via a cable. If you're careful and take photos of how the cable and hoses connect, if you do not unscrew the Throttle Position Sensor (TPS), and if you're careful not to scratch the throttle body (TB) mounting surfaces, you shouldn't cause any problems. Use Throttle Body Cleaner and a soft brush on both sides of the butterfly valve (the inside will be far dirtier than the outside).

While you have the TB out, also clean the carbon from the EGR port on the underside of the intake manifold (assuming your car is equipped with an EGR system). See the photos at the link below:

Throttle Body & EGR Port

The TPS tells the Engine Control Module (ECM) and Transmission Control Module (TCM) the degree to which the throttle valve is open. The TPS is mounted on the underside of the TB, and because of this location and the fact that the crankcase breathing system feeds oily fumes into the TB, some of this dirty oil works its way down the shaft of the butterfly valve and into the TPS. The TPS is a potentiometer or variable resistor, wired as a voltage divider. It relies on proper contact between the metal wiper and circular tracks made of conductive plastic. Any oil or other gunk interferes with this contact and can cause malfunction of the TPS. So while you have the TB out, it's a good idea to carefully drill drain holes in the TPS case and flush it out with zero-residue electrical contact cleaner spray and compressed air (if available). See the photos at this link:

Throttle Position Sensor Drain Holes

Once you reinstall the TB, it would be a good idea to check the throttle cable for any slack, and adjust if necessary. See the photos here:

Throttle Cable Adjustment

Cheers,

Don

 

Don you hero! That's everything I've been looking for! Thank you so so much . I notice most of the thumbnails are visible but clicking on them doesn't reveal the larger image, have the files been moved?