Idle speed

plumbfisher · Jul 21, 2014

Good morning, what reduces the idle speed after initial start up? I've previously asked about the idle speed and how to adjust it (2001 2.5 DT) and am told that it can be done through diagnostics. Mine starts up fine and initially runs at about 900 or so. I believe that this is then meant to drop back to around 750, but it doesn't. It stays around 900 and just sounds and feels to high. It runs sweetly and the operating temperature is fine. I'd appreciate some advice please. Should I get into diagnostics and adjust the idle speed or is there something else to look at first? Thanks

Saint.V8 · Jul 21, 2014

Idle speed is set by the engine ECU and is adjusted using diagnostics.

Idle should be set once the FIP has been correctly timed.

plumbfisher · Jul 21, 2014

Thanks Saint. Sorry ... FIP?

Datatek · Jul 21, 2014

plumbfisher said:
Thanks Saint. Sorry ... FIP?

Engine temperature sensor failed maybe. Idle speed is 750 +/- 50rpm.
Really needs looking at on diagnostics.

plumbfisher · Jul 21, 2014

The temp when running is good, and hot start is no problem. as I say it all runs quite sweetly. What else does the engine temperature sensor control apart from idle speed? and what is FIP?

Datatek · Jul 21, 2014

plumbfisher said:
The temp when running is good, and hot start is no problem. as I say it all runs quite sweetly. What else does the engine temperature sensor control apart from idle speed? and what is FIP?

Sensor for the gauge is not the same as the sensor for the ECU.

Saint.V8 · Jul 21, 2014

plumbfisher said:
The temp when running is good, and hot start is no problem. as I say it all runs quite sweetly. What else does the engine temperature sensor control apart from idle speed? and what is FIP?

FIP....Fuel Injection Pump

plumbfisher · Jul 21, 2014

So.. the sensor is for the ECU, and the ECU runs the FIP. If the engine is running fine then presumably the FIP is set fine. So the idle speed alone can be adjusted?

Datatek · Jul 21, 2014

plumbfisher said:
So.. the sensor is for the ECU, and the ECU runs the FIP. If the engine is running fine then presumably the FIP is set fine. So the idle speed alone can be adjusted?

If the ECU engine temperature sensor is faulty, it may think the engine is permanantly cold. Sort that before you go fiddling with the idle speed. Tacho is not that accurate either, on diagnostics, mine idles at 750, tacho shows 800rpm

plumbfisher · Jul 21, 2014

If the ECU thinks that the engine is cold what else would the ECU do? Will it alter FIP settings? or glowplug timers? Will a faulty sensor show up on diagnostics? Later this week I'm taking the old jalopy to good independent garage who has got diagnostics for P38s. But I want to know what it is that I need to ask him to do! Thanks for your help

Datatek · Jul 21, 2014

plumbfisher said:
If the ECU thinks that the engine is cold what else would the ECU do? Will it alter FIP settings? or glowplug timers? Will a faulty sensor show up on diagnostics? Later this week I'm taking the old jalopy to good independent garage who has got diagnostics for P38s. But I want to know what it is that I need to ask him to do! Thanks for your help

It should light the glowpugs as if you have a hot start fix, however it will depend on just what is going on. You can see the both Temperature sensors on diagnostics, you can also look a FIP modulation, fuel temperature etc. There are a number of things in the Fip that might affect idle as there is in the EDC. Wammers is your man for the FIP but he's away.
You could try unplugging the MAF to see if affects it, also worth looking at the EGR valve, not sure if it could affect it but the do get gunged up and stick. If you take the rubber pipe off it, it will stay closed if it's not stuck and the car will run better.

plumbfisher · Jul 22, 2014

Thanks for that. I'll post again after diagnostics, it'll be interesting to see what comes up

plumbfisher · Jul 25, 2014

plumbfisher said:
Thanks for that. I'll post again after diagnostics, it'll be interesting to see what comes up

Well he came up with the 'inlet air temperature sensor'. It is obviously not right, showing -38.88 all the time. This will apparently result in overfuelling (running on choke) on idle but is evened out when motoring due to more fuel being needed. If left on idle for a long time it would sooty things up (and use a lot of fuel). So - IAT sensor. Behind the front grill, by the intercooler apparently. Anyone changed one? Is it much of a job? Do you think this might be the problem? (quite reassured by the fact that there were no fault codes or anything else come up, so by process of elimination...?)
Thanks for help

wammers · Jul 25, 2014

plumbfisher said:
Well he came up with the 'inlet air temperature sensor'. It is obviously not right, showing -38.88 all the time. This will apparently result in overfuelling (running on choke) on idle but is evened out when motoring due to more fuel being needed. If left on idle for a long time it would sooty things up (and use a lot of fuel). So - IAT sensor. Behind the front grill, by the intercooler apparently. Anyone changed one? Is it much of a job? Do you think this might be the problem? (quite reassured by the fact that there were no fault codes or anything else come up, so by process of elimination...?)
Thanks for help

If it is a EGR engine that is normal. It is a preset and NOT a fault.

plumbfisher · Jul 25, 2014

Sorry, I should have said. Yes it is a 2.5 with EGR. So should I now look at the MAF sensor? tho' nothing came up about that. I took a pic(of the diagnostics screen) but am not sure how to post a pic on here.

wammers · Jul 25, 2014

plumbfisher said:
Sorry, I should have said. Yes it is a 2.5 with EGR. So should I now look at the MAF sensor? tho' nothing came up about that. I took a pic(of the diagnostics screen) but am not sure how to post a pic on here.

That has nothing to do with fueling either it just measures airflow for ECU to run the EGR. Idle should be 750 +_ 50 RPM. Can be set with diag has anyone played with the pump?

plumbfisher · Jul 25, 2014

wammers said:
That has nothing to do with fueling either it just measures airflow for ECU to run the EGR. Idle should be 750 +_ 50 RPM. Can be set with diag has anyone played with the pump?

I don't know if anyone has messed with the pump. I think probably not as up until now it has been serviced by the same main dealers since new.
Idle speed is 840 odd. (I'll try attaching the pic...)

plumbfisher · Jul 25, 2014

He also said that he couldn't reset it on his diagnostic thing (It was a Snap On, then he tried another one. The pic is of that screen)

wammers · Jul 25, 2014

plumbfisher said:
He also said that he couldn't reset it on his diagnostic thing (It was a Snap On, then he tried another one. The pic is of that screen)

You need Nanocom or something similar if you have hot fix fitted disconnect it it maybe stuck on. Do glow lamps come on hot or cold?

Datatek · Jul 25, 2014

plumbfisher said:
Well he came up with the 'inlet air temperature sensor'. It is obviously not right, showing -38.88 all the time. This will apparently result in overfuelling (running on choke) on idle but is evened out when motoring due to more fuel being needed. If left on idle for a long time it would sooty things up (and use a lot of fuel). So - IAT sensor. Behind the front grill, by the intercooler apparently. Anyone changed one? Is it much of a job? Do you think this might be the problem? (quite reassured by the fact that there were no fault codes or anything else come up, so by process of elimination...?)
Thanks for help

That is the sensor for the HEVAC display.

Idle speed

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