240 General: - Engine starts, idles rough then stalls - Page 2

DW42 · Oct 6th, 2022, 05:39

So what do we know? The problem had a sudden onset with a warm engine, which will subsequently run badly. Computer says sensors are okay. This suggests that the crank position sensor is fine. Two possibilities which come to mind is that the timing belt has slipped a notch, or the ignition amplifier broke (it's on the fender, on the intake side). You can check the timing belt yourself by removing the top part of the plastic cover. These are the best instructions I could find (for a 740, same engine as a 240).
https://www.brickboard.com/RWD/volvo...t_slipped.html

If you plan to keep your 240 it's not a bad idea to buy the following spares: fuel pump relay, ignition amplifier, crank position sensor, MAF. There are probably some other things, but these are failures that can strand you. New MAFs are expensive, but it may still be possible to get a good used one.

Clifford Pope · Oct 6th, 2022, 08:28

I absolutely agree with DW42. I have in past over several years and different 240s been suddenly let down by all the items he lists. They are all relatively cheap, and at some stage will fail and need replacing, so it's not money wasted.
They are some of the few components where replacing them one at a time is the best way of diagnosis. If it works, problem solved, if it doesn't, you know that existing component can be put back on and the new one kept in the car for another day.

Ignition Amplifier Module - the car had been running perfectly, until it suddenly cut out coming up the hill to home, and refused to re-start. The IAM takes only seconds to swap (see my other recent post on keeping a spare ready-screwed to its heat sink) and the car then restarted immediately.

Crank Position Sensor - this had been causing intermittent refusal to start, but it always did in the end after waiting a few minutes, and it then ran normally. It is the worst one to replace - very fiddly, you need slim agile fingers, exactly the right slim socket and extension, and it is very easy to drop and lose the fixing screw.
The wiring degrades over time, not helped by any oil seepage from the back of the block.

Fuel pump relay. Very likely suspect. The easiest diagnosis is to keep a 6" bit of wire in the car with a crocodile clip on each end. Simply join the terminals of fuses 4 and 6 together, and it bypasses the relay and the pumps will then run continuously. (door side, ie left of the fuse board).
Very much a get you home measure - disconnect when home.

There are lots of other possible causes of course, but these in most people's experience are the most common I think.
Needless to say all the old tried and tested things apply - spark plugs, HT leads, coil, rotor arm, earth connections.

I'm not convinced about the usefulness of the on-board diagnostics. None of my faults have ever shown up a code, but I have had false indications that simply cured themselves by cancelling the light and re-starting.

jackgeo · Oct 6th, 2022, 20:34

Thanks for the help guys, i'll check the things that have been mentioned this weekend and order some of the parts you have listed. as you say, even if a replacement part doesnt fix it, its always good to have.

SnineT · Oct 7th, 2022, 07:14

Start with the crank sensor as it seems the most likely culprit out of those listed by others.

jackgeo · Oct 8th, 2022, 21:33

Ok so yesterday i removed and cleaned the throttle body and refitted it with a new gasket. It started and didnt stall! it idled quite high but it might just need adjusting? and it restarted when it was warm. but it does idle a bit weird, if i rev the engine a bit and release the pedal the revs stay high and i need to stamp the pedal for it to come back down again, almost like it gets stuck open. Im not sure if its the choke or something? i forgot to mention that it has done that on and off since i got the car.

I also have a feeling that its running quite rich, fuel economy isnt great and it does smell a bit of petrol. i dont have much experience so i might be wrong, but could that be why the throttle/intake was so black? and why the low idle is quite erratic? Im just thinking out loud really.

360beast · Oct 8th, 2022, 22:50

I'd be suspicious of the ECT (Engine coolant temperature sensor) it is under the inlet manifold and it goes in to the head, there are two sensors under there the one towards the front of the engine is for the gauge and the one towards the back is for the ECU.

When they start to go they can cause all sorts of weird running issues, a quick way to check it is with a multimeter on a resistance setting. Pull the plug off the sensor and put one probe on a sensor pin and the other earthed on the head or alternator, the resistance should be 327+/-37 Ohms at 80°C or 2500ohms +/- 250ohms at 20°C, check both pins.

However even these resistance figures can't be relied upon as mine checked out fine on the resistance settings yet when I started my 940 it would run fine for about 5 seconds then start misfiring, if I left it for about a minute it would clear and run fine or if I drove off the moment the oil pressure light went out it would stumble as I pulled away and then run fine. It would only do this on a cold start, I too had no fault codes (1997 940 but also runs LH2.4) so I ended up fault tracing and finding nothing so I ended up thinking "what does the ECU read when cold" and there is only one sensor that affects the fueling for LH2.4 when cold and that's the ECT.

As your problem happens when it is up to temperature you could also suspect the lambda sensor as once the ECU knows the engine has reached operating temperature it then starts taking information from the lambda sensor to fine-tune the fuelling.

I would also do a basic idle setting and make sure the throttle reel is clean as they get gummed up with old oil and filth which I have seen several times causing the throttle to stick.

DW42 · Oct 9th, 2022, 04:41

Also check again for vacuum leaks. A common place for them is the big accordion hose attached to the MAF. A cracked accordion hose can let a lot of unmetered air in. If you find a split, duct tape will usually suffice for a while.

Clifford Pope · Oct 9th, 2022, 08:37

" if i rev the engine a bit and release the pedal the revs stay high and i need to stamp the pedal for it to come back down again, almost like it gets stuck open."

Classic symptoms of a sticking Idle Air Valve. Mine does exactly this about once a year, and is cured simply by removing the valve (alloy can about the size of a brasso tin, underneath the inlet manifold) and cleaning with WD40, petrol or carb cleaner.
I use a fine paintbrush to clean the accumulated black film off the shutter. Use the wooden stick of the brush to rotate the activator (non-scratchy) and check that it closes with a nice clack noise.
Note that it doesn't shut completely - there is a small slit opening in its rest position. You can test it by applying 12v to the terminals.

Have you cleaned out the inlet manifold nozzle for the thin rubber pipe and the flame trap it connects to? (black plastic thing looking like a party-popper)

Bob 1967 · Oct 9th, 2022, 18:42

Dirt is always the first thing to get rid of before any worthwhile analysis can be completed.
It affects all aspects of the fuel/air mixture and can change the size of jets, intakes and breather hoses.
It can save time and money, rather than buying unnecessary parts, clean and lubricate everything first, then check for adjustments.

jackgeo · Oct 30th, 2022, 20:29

Well damn, thanks for the help anyway everyone :`(

Oct 6th, 2022, 05:39	#11
DW42 Senior Member Last Online: Oct 9th, 2022 04:41 Join Date: Feb 2011 Location: Currumbin, Queensland	So what do we know? The problem had a sudden onset with a warm engine, which will subsequently run badly. Computer says sensors are okay. This suggests that the crank position sensor is fine. Two possibilities which come to mind is that the timing belt has slipped a notch, or the ignition amplifier broke (it's on the fender, on the intake side). You can check the timing belt yourself by removing the top part of the plastic cover. These are the best instructions I could find (for a 740, same engine as a 240). https://www.brickboard.com/RWD/volvo...t_slipped.html If you plan to keep your 240 it's not a bad idea to buy the following spares: fuel pump relay, ignition amplifier, crank position sensor, MAF. There are probably some other things, but these are failures that can strand you. New MAFs are expensive, but it may still be possible to get a good used one. __________________ Present: 1990 240GL saloon, 1992 240 estate Past: 1988 240GL; 1971 144DL; 1972 145DL

Oct 6th, 2022, 08:28	#12
Clifford Pope Not an expert but ... Last Online: Today 10:08 Join Date: Dec 2001 Location: Boncath	I absolutely agree with DW42. I have in past over several years and different 240s been suddenly let down by all the items he lists. They are all relatively cheap, and at some stage will fail and need replacing, so it's not money wasted. They are some of the few components where replacing them one at a time is the best way of diagnosis. If it works, problem solved, if it doesn't, you know that existing component can be put back on and the new one kept in the car for another day. Ignition Amplifier Module - the car had been running perfectly, until it suddenly cut out coming up the hill to home, and refused to re-start. The IAM takes only seconds to swap (see my other recent post on keeping a spare ready-screwed to its heat sink) and the car then restarted immediately. Crank Position Sensor - this had been causing intermittent refusal to start, but it always did in the end after waiting a few minutes, and it then ran normally. It is the worst one to replace - very fiddly, you need slim agile fingers, exactly the right slim socket and extension, and it is very easy to drop and lose the fixing screw. The wiring degrades over time, not helped by any oil seepage from the back of the block. Fuel pump relay. Very likely suspect. The easiest diagnosis is to keep a 6" bit of wire in the car with a crocodile clip on each end. Simply join the terminals of fuses 4 and 6 together, and it bypasses the relay and the pumps will then run continuously. (door side, ie left of the fuse board). Very much a get you home measure - disconnect when home. There are lots of other possible causes of course, but these in most people's experience are the most common I think. Needless to say all the old tried and tested things apply - spark plugs, HT leads, coil, rotor arm, earth connections. I'm not convinced about the usefulness of the on-board diagnostics. None of my faults have ever shown up a code, but I have had false indications that simply cured themselves by cancelling the light and re-starting. Last edited by Clifford Pope; Oct 6th, 2022 at 08:32.

Oct 9th, 2022, 04:41	#17
DW42 Senior Member Last Online: Oct 9th, 2022 04:41 Join Date: Feb 2011 Location: Currumbin, Queensland	Also check again for vacuum leaks. A common place for them is the big accordion hose attached to the MAF. A cracked accordion hose can let a lot of unmetered air in. If you find a split, duct tape will usually suffice for a while. __________________ Present: 1990 240GL saloon, 1992 240 estate Past: 1988 240GL; 1971 144DL; 1972 145DL

Oct 9th, 2022, 18:42	#19
Bob 1967 Master Member Last Online: Jun 5th, 2024 00:42 Join Date: Aug 2017 Location: Dublin View Photos By: Bob 1967	Dirt is always the first thing to get rid of before any worthwhile analysis can be completed. It affects all aspects of the fuel/air mixture and can change the size of jets, intakes and breather hoses. It can save time and money, rather than buying unnecessary parts, clean and lubricate everything first, then check for adjustments. __________________ Cowboy used to be a trade , now it means lack of one.

Oct 6th, 2022, 20:34	#13
jackgeo New Member Last Online: Dec 8th, 2022 18:53 Join Date: Oct 2022 Location: Saffron Walden	Thanks for the help guys, i'll check the things that have been mentioned this weekend and order some of the parts you have listed. as you say, even if a replacement part doesnt fix it, its always good to have.

Oct 7th, 2022, 07:14	#14
SnineT Extrahumanestrial Last Online: Feb 13th, 2023 19:02 Join Date: Jun 2022 Location: Budapest	Start with the crank sensor as it seems the most likely culprit out of those listed by others.

Oct 8th, 2022, 21:33	#15
jackgeo New Member Last Online: Dec 8th, 2022 18:53 Join Date: Oct 2022 Location: Saffron Walden	Ok so yesterday i removed and cleaned the throttle body and refitted it with a new gasket. It started and didnt stall! it idled quite high but it might just need adjusting? and it restarted when it was warm. but it does idle a bit weird, if i rev the engine a bit and release the pedal the revs stay high and i need to stamp the pedal for it to come back down again, almost like it gets stuck open. Im not sure if its the choke or something? i forgot to mention that it has done that on and off since i got the car. I also have a feeling that its running quite rich, fuel economy isnt great and it does smell a bit of petrol. i dont have much experience so i might be wrong, but could that be why the throttle/intake was so black? and why the low idle is quite erratic? Im just thinking out loud really.

Oct 8th, 2022, 22:50	#16
360beast Go redblock or go home Last Online: Today 09:51 Join Date: Feb 2012 Location: UK	I'd be suspicious of the ECT (Engine coolant temperature sensor) it is under the inlet manifold and it goes in to the head, there are two sensors under there the one towards the front of the engine is for the gauge and the one towards the back is for the ECU. When they start to go they can cause all sorts of weird running issues, a quick way to check it is with a multimeter on a resistance setting. Pull the plug off the sensor and put one probe on a sensor pin and the other earthed on the head or alternator, the resistance should be 327+/-37 Ohms at 80°C or 2500ohms +/- 250ohms at 20°C, check both pins. However even these resistance figures can't be relied upon as mine checked out fine on the resistance settings yet when I started my 940 it would run fine for about 5 seconds then start misfiring, if I left it for about a minute it would clear and run fine or if I drove off the moment the oil pressure light went out it would stumble as I pulled away and then run fine. It would only do this on a cold start, I too had no fault codes (1997 940 but also runs LH2.4) so I ended up fault tracing and finding nothing so I ended up thinking "what does the ECU read when cold" and there is only one sensor that affects the fueling for LH2.4 when cold and that's the ECT. As your problem happens when it is up to temperature you could also suspect the lambda sensor as once the ECU knows the engine has reached operating temperature it then starts taking information from the lambda sensor to fine-tune the fuelling. I would also do a basic idle setting and make sure the throttle reel is clean as they get gummed up with old oil and filth which I have seen several times causing the throttle to stick.

Oct 9th, 2022, 08:37	#18
Clifford Pope Not an expert but ... Last Online: Today 10:08 Join Date: Dec 2001 Location: Boncath	" if i rev the engine a bit and release the pedal the revs stay high and i need to stamp the pedal for it to come back down again, almost like it gets stuck open." Classic symptoms of a sticking Idle Air Valve. Mine does exactly this about once a year, and is cured simply by removing the valve (alloy can about the size of a brasso tin, underneath the inlet manifold) and cleaning with WD40, petrol or carb cleaner. I use a fine paintbrush to clean the accumulated black film off the shutter. Use the wooden stick of the brush to rotate the activator (non-scratchy) and check that it closes with a nice clack noise. Note that it doesn't shut completely - there is a small slit opening in its rest position. You can test it by applying 12v to the terminals. Have you cleaned out the inlet manifold nozzle for the thin rubber pipe and the flame trap it connects to? (black plastic thing looking like a party-popper)

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