air intake temperature sensor

MGT · Apr 8, 2025

I have just swapped the air intake temperature sensor on a relative's freelander 1 (td4) hoping it would clear white/grey smoke on starting (after reading recent thread). Just started it this morning to test and the smoke is still there but now it cleared quicker.

It was clearing before when the engine warmed up but taking longer than it did this morning.

Question is: does it take a while for the system to get used to the new sensor or should I expect the smoke to not be there at all IF the sensor was the problem, or only problem?

The problem appears well known - rough idle with smoke on cold engine, clears when driven. Likely culprit: failed temp sensor.

Arctic2 · Apr 8, 2025

Could be an injector, glow plugs, how old is the air filter, as a leak back test been done, quite a few Fl1 do this and i almost sure no one as solved it.

MGT · Apr 8, 2025

Arctic2 said:
Could be an injector, glow plugs, how old is the air filter, as a leak back test been done, quite a few Fl1 do this and i almost sure no one as solved it.

I wondered about glow plug. It idles fine and does not smoke once engine is warm.

How could it be an injector though? Surely if it drips it is going to drip whether engine is warm or cold.

I'll do leak back test tomorrow anyway. Thanks for reply.

Any tips on replacing glow plugs? I've read they can snap quite easily.

GrumpyGel · Apr 8, 2025

MGT said:
I wondered about glow plug. It idles fine and does not smoke once engine is warm.

How could it be an injector though? Surely if it drips it is going to drip whether engine is warm or cold.

I'll do leak back test tomorrow anyway. Thanks for reply.

Any tips on replacing glow plugs? I've read they can snap quite easily.

I suppose if the engine is cold, its had longer to let more drips in.

Don't know if much pressure stays in the rail once the engine is cut.

Also don't know much about what goes on inside the cylinders, but the injectors fire fuel in a very fine mist so that it ignites better. 'Liquid' diesel will not burn so easily and will burn or pass through as smoke.

My L Series isn't common rail, but when warm it starts with no smoke. Leave it a day and there's a decent puff of smoke, leave it a few days and there's a cloud of smoke. It always starts on the button though, its not like its turning over and filling the cylinders with diesel, so glow plugs are not the issue. It also just knocks out that puff, or cloud, and clears almost immediately, so its not related to temp sensors as nothing will have changed that quickly.

I say the smoke clears immediately, but it does run a bit smokey, particularly if the GO peddle (OK its an L Series, the go a bit quicker peddle) is pressed, but its not like start up.

MGT · Apr 8, 2025

GrumpyGel said:
I suppose if the engine is cold, its had longer to let more drips in.

Don't know if much pressure stays in the rail once the engine is cut.

Also don't know much about what goes on inside the cylinders, but the injectors fire fuel in a very fine mist so that it ignites better. 'Liquid' diesel will not burn so easily and will burn or pass through as smoke.

My L Series isn't common rail, but when warm it starts with no smoke. Leave it a day and there's a decent puff of smoke, leave it a few days and there's a cloud of smoke. It always starts on the button though, its not like its turning over and filling the cylinders with diesel, so glow plugs are not the issue. It also just knocks out that puff, or cloud, and clears almost immediately, so its not related to temp sensors as nothing will have changed that quickly.

I say the smoke clears immediately, but it does run a bit smokey, particularly if the GO peddle (OK its an L Series, the go a bit quicker peddle) is pressed, but its not like start up.

Interesting. Maybe drips after engine stopped. I don't know if that's possible when injectors seem to be running fine when car is going. No other hint one or more might be duff. But I don't know anything much about the internals of an injector.
Glow plugs heat the interior of the combustion chamber to compensate for low temperature of engine on start up, so if a glow plug is not working that atomised diesel won't ignite until the engine is warm. That's my reason for thinking it's a glow plug.

I've just taken it for a good thrashing down the motorway so I will see if that makes a difference when i start it in the morning.

Arctic2 · Apr 9, 2025

MGT said:
I wondered about glow plug. It idles fine and does not smoke once engine is warm.

How could it be an injector though? Surely if it drips it is going to drip whether engine is warm or cold.

I'll do leak back test tomorrow anyway. Thanks for reply.

Any tips on replacing glow plugs? I've read they can snap quite easily.

My Tip on changing the glow plugs is do it wen the engine is hot, remove the manifold which means you have to remove the air duct, EGR so while you have all that off clean out the Manifold, wipe MAP sensor clean, clean EGR.

When removing the glow plugs make sure you use a good six sided socket and a decent ratchet, put some plus gas round the plugs before starting, or even a day or so before if you can.

Once the manifold is off unplug the wiring to each glow plug, doing one at a time.

1

I like using a long ratchet with a good six sided socket.

2

Turn it very slowly so you get the feel if the glow plug in undoing or twisting if it's tight undo then tighten back up keep doing this until it freely moving and come out.

3

4

Put some ceramic grease on the thread of the new glow plug, if you do not have any use copper grease, white ceramic is better.

5

Insert an the nip it up do not over tighten the glow plugs.

6

7

Do each one in turn good luck.

8

Also when was the fuel filter last changed, and the sedimenter last drained to see if there is any water in the fuel.

9

10

MGT · Apr 9, 2025

Thanks Arctic. I think glow plugs are the next step. There's no smoke at all after I've gone a mile down the road, either at speed or at idle, so I don't see how it can be anything else. Mind you, Haynes does say a bad injector spray pattern can damage the glow plugs, and I wouldn't say the engine is exactly purring. Something feels slightly off. The idle, even when it's not lumpy once engine has warmed, is more of a throb than I am used to. This one is an automatic though, and mine is a manual.

Out of interest, would a bad glow plug throw up a fault code? I've been thinking about getting a diagnostic kit to save a bit of guesswork.

I haven't changed the fuel filter on this one so I expect it has been on for quite a while. What's the thinking there - that overnight water could be getting into the fuel via condensation, not being drained out because of full sedimenter, then being burned off into smoke on start up?

Arctic2 · Apr 9, 2025

I sure Nodge tried solving this on his TD4 and a few others but could not find a solution to the early first start up of smoke, funny thing is the Rover 75 diesel with virtually the same engine doesn't have this problem, glow plugs do not always show a fault on the diagnostic but you can test them by using a multi meter.

Also check the glow plug relay.

glow plug test.

MGT · Apr 9, 2025

Arctic2 said:
I sure Nodge tried solving this on his TD4 and a few others but could not find a solution to the early first start up of smoke, funny thing is the Rover 75 diesel with virtually the same engine doesn't have this problem, glow plugs do not always show a fault on the diagnostic but you can test them by using a multi meter.

Also check the glow plug relay.

glow plug test.

If Nodge couldn't sort it then I've got no chance. It's irritating though.

Thanks for the added input re testing the glow plugs.

edit - just watched that video you posted and those are the exact symptoms I am getting. I think that is as close to a racing certainty as I can get. I will swap the lot while I am in there.

Thanks very much.

Nodge68 · Apr 9, 2025

MGT said:
I wondered about glow plug. It idles fine and does not smoke once engine is warm.

How could it be an injector though? Surely if it drips it is going to drip whether engine is warm or cold.

I'll do leak back test tomorrow anyway. Thanks for reply.

Any tips on replacing glow plugs? I've read they can snap quite easily.

If an injector isn't sealing tight, then the injector will leak fuel into the bowl of the piston. This will then take time to burn off once started, as diesel has to be atomised or hot to burn.
If the smoke is slightly blue, then it's likely valve guide seals on the intake valves letting oil past overnight, which again will take time to be drawn in and burn. Once the engine is hot, the seals seal better, and the intake is under boost, helping to keep oil out the intake.

Nodge68 · Apr 9, 2025

MGT said:
If Nodge couldn't sort it then I've got no chance. It's irritating though.

Thanks for the added input re testing the glow plugs.

edit - just watched that video you posted and those are the exact symptoms I am getting. I think that is as close to a racing certainty as I can get. I will swap the lot while I am in there.

Thanks very much.

I had the dreaded 2k misfire, I even posted a video on YT to show it.

I changed the plugs, injectors, HP pump, and all the boost hoses, and couldn't cure it.
The gearbox crapped out before I could go any further with it, but I had a suspicion is was related to the PCV system, but never got to try out any of the ideas I had, as the FL2 came along.

MGT · Apr 9, 2025

Nodge68 said:
If an injector isn't sealing tight, then the injector will leak fuel into the bowl of the piston. This will then take time to burn off once started, as diesel has to be atomised or hot to burn.
If the smoke is slightly blue, then it's likely valve guide seals on the intake valves letting oil past overnight, which again will take time to be drawn in and burn. Once the engine is hot, the seals seal better, and the intake is under boost, helping to keep oil out the intake.

So another two possibilities.

There's no doubt the idle remains rough even when the smoke has cleared after a run. So although the symptoms look identical with those on that video Arctic posted once the engine is warmed the glow plug input has ceased, so something else must be causing it.

I think from what you said the order should be to check injectors first then do the glow plugs if necessary. I don;t much fancy risking snapping a glow plug if that's not the root cause.

Well, first another air temperature sensor in case the one I swapped out was less than perfect (it was from a donor vehicle), then injectors, then glow plugs.

Thanks for your advice, Nodge.

MGT · Apr 9, 2025

Nodge68 said:
I had the dreaded 2k misfire, I even posted a video on YT to show it.

I changed the plugs, injectors, HP pump, and all the boost hoses, and couldn't cure it.
The gearbox crapped out before I could go any further with it, but I had a suspicion is was related to the PCV system, but never got to try out any of the ideas I had, as the FL2 came along.

That's quite a lot of work for no reward. I'm my own worst enemy - the only reason there's another freelander 1 in the family is because I recommended them. SO now I get to fix the damn thing.

MGT · Friday at 16:57

Thought i would post an update as I've made progress.

On another recent thread someone posted that the air intake temperature sensor works in tandem with the MAP sensor, and I can confirm that if you just replace the temperature sensor without checking the intake manifold and MAP sensor for carbon build up it may not clear rough idle.

Once I had the manifold and MAP sensor off and mostly cleared of a huge amount of carbon build up the rough idle and much of the smoke on start up has gone. I'm hoping the smoke clears completely and will report back if it does.

When I took the MAP sensor off and pushed a screwdriver into the hole in the end of the manifold it went through a solid wall of carbon (the sensor was also plugged solid), so there was no way the sensor was functioning.

Arctic2 · Saturday at 01:11

I can't even remember how many manifold EGR and MAP sensors i have removed and changed over for cleaned out ones, it goes a long way to keeping the smoke to a minimum, and will certainly help the rough idle, but weather it will stop the puff of smoke on start up is another thing.

been changing them and cleaning then since 2012

1

2

3

4

MAP sensor

5

EGR.

6

7

8

9

seen some really bad ones, i can only imagine how many FL1 and R40 are running around out there with the manifold EGR and MAP sensor clogged up and choking the engine.

10

MGT · Saturday at 13:10

Arctic2 said:
I can't even remember how many manifold EGR and MAP sensors i have removed and changed over for cleaned out ones, it goes a long way to keeping the smoke to a minimum, and will certainly help the rough idle, but weather it will stop the puff of smoke on start up is another thing.

been changing them and cleaning then since 2012

1

2

3

4

MAP sensor

5

EGR.

6

7

8

9

seen some really bad ones, i can only imagine how many FL1 and R40 are running around out there with the manifold EGR and MAP sensor clogged up and choking the engine.

10

Pretty much what I am finding. I was hoping smoke would disappear but it was still smoking on cold start this morning. Just the rough idle has reduced and there is no smoke when warm

So I guess two issues at work. Next stop will be to replace glow plugs when I can get car back.

air intake temperature sensor

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