p38 4.6 idle probs

hi guys my p38 as a problem again when i start from cold revs over 2000 revs worried over the lack ov oil around the engine overnight then starting it on a morning as it revs 2000 and above sometimes when really hot the revs seem right about 850 if i turn it off sometimes it will start normal and sometimes rev high like there`s air leaking iv`e had my inlet manifold off and replaced the gaskets i`m pointing to the stepper motor anyone had this problem before i part with more money oh i took the stepper out and cleaned the seat

Make sure there is plenty of free play on the throttle cable.

hi m8 thanx for the reply iv`e checked the play on the cable seems fine from cold lots ov play stays the same when started ? anymore ideas what i could do to rule out the stepper motor the purge would not cause these problems would they

one poss cause could be the temp sender for the ecu similar problem for most of the rover brand steve t

cheers m8 already changed that and still the same went and brought a new stepper motor yesterday put it in still the same

Check the vaccum hoses for splits etc. and get an emission check to see if the Air Flow Meter is working correctly

thanx m8 but already done that i'm thinking that the ecu may need re setting by taking the battery off for 12 hrs now i've fitted the new stepper motor see if that makes any diff . emission's are all ok and no faults showing when tested

Is your car running LPG ?

yeah but i've disconected the lpg as the fault started when it was on i've re joined the wires from the ecu so there is no gas on there now but it's still reving to high

See if you can get the ECU reset to default mode by someone with Rovacom or Autologic so it will have to self learn. An easy job-takes all of 10minutes. This will put it back to factory settings.

Re-my last reply-leave the LPG system totally disconnected cos they ran on petrol when they came off the line!!

You need to get it on Testbook,check what the stored closed throttle position voltage is and then look at the actual output with the throttle closed.I reckon that for some reason the ecu is not seeing a voltage equal to or less than the stored voltage.In this state the ecu will not try to control the idle and will leave the stepper jacked open,ready to bring the speed down slowly and accept whatever loads are present.
A faulty throttle position sensor is favourite,but you'll need to check it all out.The stored voltage can be reset on Testbook either on its own or with all the other ecu adaptions.Probably a good idea to do all of them as your LPG will usually upset the long term fuel trims after several months of use.

ave just bin in touch with a guy by me said e will ave it in on tuesday cheers m8 hope this works now your LPG will usually upset the long term fuel trims after several months of use.
sorry to sound thick what do you mean by this and in what form will it up set

What the problem is,is that the petrol ecu still thinks it is fuelling the engine whilst its on LPG.Because It is an adaptive system it has the function to alter injector pulse widths to compensate for engine wear etc.It uses short and long term trims,what happens is the LPG system is not as clever or accurate as the petrol system so the feedback from the oxygen sensors and knock sensors is not what the petrol ecu is expecting to see.For instance if the LPG vaporiser starts to gum up and be unable to supply enough gas the oxygen sensors will give a lean signal.The petrol ecu sees this and widens the injector pulse width to get it to switch rich,but because it is not actually injecting any fuel the signal stays lean.
Over a period of time this makes the long term trims very rich - so when you switch back to petrol it will run rich all the time because it has "learnt" to the rich side of the values and the short term trims wont come back far enough from the long term baseline to compensate.
I have a customer with a 4.0v8 with an OMVL dream sequential system that needs a reset every 6 months - not because there is any big problem with the gas,just that he knows its not quite right. Its here at my workshop now waiting for a new exhaust and reset - for me it is annoying because the gas has been set up very carefully and I check it each time,its just not quite good enough.
Sorry to dribble on but I hope its a bit more clear now.

yeah bit better now thanx 4 your help if you were closer then i could ave got you to look at it for me but not to worry it's goin in on tuesday

Hi ,

My father has the same problem with his 4.0. But it is not running on gas. The adaptive values for the closed throttle position keep getting over written, We keep reseting the values with autologic. and maybe it will last a few days. but sometimes it will only behave for a few hours. We have just fitted a new throttle potentiometer. but it is still messing about. We have been throw the basics. air leaks etc. but still no joy.

Any ideas?

Bryan

P38 Owner said:

Hi ,

My father has the same problem with his 4.0. But it is not running on gas. The adaptive values for the closed throttle position keep getting over written, We keep reseting the values with autologic. and maybe it will last a few days. but sometimes it will only behave for a few hours. We have just fitted a new throttle potentiometer. but it is still messing about. We have been throw the basics. air leaks etc. but still no joy.

Any ideas?

Bryan

Click to expand...

Thats an odd one,what do the values go back to - is it always the same value ? Are you reseting all the adaptions or just the stored closed throttle position ?

The value changes from every time it has not been the same number yet. its not the same common figger. I think he is only resetting the throttle position value. We thought it was getting a mixed signal from the throttle potentiometer and it gets confussed on were its closed throttle postion point is. But to add to the snag. it seams to be doing it when ever it likes know. some times you can start it and it ticks over at 750 - 800 revs fine drive it around all day and when you pull up to a road junction. the revs are high, around the 2000 mark. Makes driving it interesting as it can catch you out. it cant be doing the autobox or the brakes much good so if anyone can help. As we have run out of ideas.

B.

i might have a few on tuesday once mine as been done but cant help until then as mine is the same .will let you no how i get on with it

cheers guys a remap and all sorted running spot on cheers