My TL magna auto has been stalling for a little while now, it sometimes cuts out when sitting at the traffic lights when the radio, aircon, headlights & indicators are on or as above when reversing. Evey now and then it would have a miss as well. My wife drives the car and has had enough. I usually just put it in neutral & the revs go up. It was time for a plug change this week so I replaced all the plugs , cleaned the throttle body, cleaned the intake manifold, put new plugs leads , checked the distributor cap, and put a new rotor button in. It is running a lot better and has virtually stopped doing it but not completely. The fuel filter is only a year old. To me it seems electrical. The car has 227,000 on it any help would be appreciated.

What is the idle speed when it threatens to cut out?

May have a dead ISC. A working one should give you a constant idle speed on a warm motor no matter what load is on it.

Easy enough to check with a multimeter.

I took the ISC out a while ago & cleaned it & it didn't help. I know it ups the rpm when the a/c is on so I assumed it was ok . It starts to die when at idle revs at about probably 700 & then drops. Seems worse when radio, a/c, indicator are on.

Sounds like your alternator (or voltage regulator in the alternator) or your battery may be failing; or you have ground cabling issues if your revs are affected by operation of electronics.
Check the voltage output of the battery and alternator for starters.

Battery is a 620 unit only a year old. I need a multi meter I think.

Does it just stall as if you turned the ignition key off, or does it hesitate/hunt and then stall?

Mine also has a periodic miss, and once just switched off as if I turned the key off (I think it is one and the same problem)

...it hunts hesitates and then stalls

Maybe fuel pump issues?

Looks like I need a multimeter by the weekend. I am really thinking electrical but I will check the pump as well.

I took the ISC out a while ago & cleaned it & it didn't help.

It starts to die when at idle revs at about probably 700 & then drops. Seems worse when radio, a/c, indicator are on.

Still sounds like a dud ISC to me.
No, cleaning a dud one doesn't help any.

But once you have a multimeter you can check it and get a definite answer on it being ok or borked.

I am not sure, but if it is the ISC I believe you can disconnect it and see if the problem persists?

I am not sure, but if it is the ISC I believe you can disconnect it and see if the problem persists?
Easier to use a multimeter and measure the resistance of the 4 coils.
All four same = ok!
One open circuit = replace!

Switching on a bunch of things like lights places a load on the alternator making it harder to turn, which will exacerbate any idling issues. My best guess is a maladjusted throttle position sensor. Since the ISC is upping the revs with AC on it would appear that the stepper motor is functional but if the TPS is out of adjustment it might not be signalling to the ECU that you are idling, so the ISC isn't instructed to govern idle speed. The TPS includes a switch that's triggered (or should be) when the throttle valve is closed, it only needs to be a little bit out for the throttle to be fully closed without tripping the switch.

Still sounds like a dud ISC to me.
No, cleaning a dud one doesn't help any.

But once you have a multimeter you can check it and get a definite answer on it being ok or borked.

Well I have a cheap and nasty multi meter I have never played with one before electrical is not my thing. How do I check the ISC & TPS? I am going to play with the car again on Sunday

Well I have a cheap and nasty multi meter I have never played with one before electrical is not my thing. How do I check the ISC & TPS? I am going to play with the car again on Sunday

ISC:
Pull the plug off the ISC connection.
You will see two rows of 3 pins.
Put the multimeter on a low range resistance measurment.
Measure from the middle pin to each of the two outer pins.
You will get 4 readings.
Write them down.
Look at them.

If all are near the same, the ISC is good.
If one reads zero, it is broken.

TPS:
Remove connector.
Measure from one pin to the next.
Actually, I don't know what order they go in, but it has:

An on/off switch.
So between 2 pins you should get zero resistance with the throttle closed, and open resistance with the throttle opened by hand slightly.

A variable resistor.
Between 2 pins, you will get in increasing resistance as the throttle is opened more. It should be a smooth increase in resistance as you slowly open the throttle.

Obviously, do this with ignition ON and the engine NOT running.

Battery/alternator check:

Multimeter on DC voltage range, must be on a range above 12 volts.

Engine off:
Measure across battery. Should get 12 Volts or more.
Turn light on. Voltage should drop down a bit.


Turn engine on.
Battery voltage should go up to 14.5V and not change too much if you turn lights on or off.

Just did the battery / alternator test - all fine. Now for the ISC & TPS

having trouble using the multimeter on the ISC any advice?

Quick update, I checked the TPS and it seemed fine so I put a new ISC in today, the old o ring was trashed (must have been when I took it out. Anyway it is now idling high . I had the same thing happen when I put an EZ boy throttle body in and it settled down after a few days. I am hoping this will be the same.