3.9 v8 idle problem

[dave]

Q for all you mechanic's

Ive got a 3.9 out of a disco, At idle motor revs fluctuate to almost a stall at times and when put in gear and loaded up by turning steering motor dies right down and stalls.
I thought it must be the stepper motor, had an auto electrician test and he said the motor is reading right resistance, but said it did feel stiff. Borrowed a steeper motor off a mate and didnt make any difference.I dont know his works properly as his motor dose not run it.
I tried disconnecting mine and manually opening it , this picked the idle speed up a little and helped slightly but the motor still goes to stall when loaded. I continued to slowly move the plunger back further which continued to increase the idle as its getting more air but this in turn makes the car harder to hold on the brakes.
The problem also seams to be worse when the motor is hot.

So my question is it just the stepper motor and a new one will fix it or is there something else that could cause my problems.

My stepper motor is moving in and out i can hear the rev change and the air sucking through the port but it dose seem slow as though when the motor dies off it cant open quick enough to stop the stall
Also motor runs fine when brought up off idle and seems to rev cleanly

[advdisco1]

air flow meter

[kitacooch]

air flow meter

X2, is common problem, check your connection as sometimes is just loose and or dirty, spray some electrical lube onto it, worth have a good one.

[dave]

Have tryed playing with the plug but ill give it a good clean up and see what happens

[chimpboy]

I had a vacuum leak causing a similar problem.

[armbrup]

The 14CUX is prone to stalling as the stepper drops steps out on hot/warm start. It is a 14CUX characteristic.
Sometimes this is caused by oil build up on the throttle blade dropping the "kerb idle", ie the idle with no stepper steps activated.
So clean the oil residue off the throttle blade , and out of the oil line stub etc with carby cleaner.
Check the kerb idle by blocking off the stepper intake and the other end on the manifold, and if necessary adjust to 550-600RPM, withe the grub screw on top of the blade.
Funny I just had this problem with mine after a dyno tune and the tuner later fixed it by dropping settings on my unichip at idle to standard, but mine still occasionally stalls when hot.
I find you have to wait until it goes through all steps, then back up to idle before putting in drive.
Regards Philip A

[stuee]

Try looking at all your spark plug and coil leads for something simple to do. I had a similar idle problem as you describe (stall when load up steering and rough idle etc) and found that one of my spark plug leads was completely corroded at the connection to the distributor cap and others were getting that way.

New rotor button, cap, leads and plugs and it was sweet again.

edit* mine was revving cleanly too, I suspect that at higher revs there was more power available for the coil which could overcome the resistance of the corrosion on the lead. Its an easy check for you though.

[dave]

I had a vacuum leak causing a similar problem.

Yer i already checked that buy spraying everything with wd to see if there was a rev change but all seemed good i dont think theres any vacum leaks.

[dave]

The 14CUX is prone to stalling as the stepper drops steps out on hot/warm start. It is a 14CUX characteristic.
Sometimes this is caused by oil build up on the throttle blade dropping the "kerb idle", ie the idle with no stepper steps activated.
So clean the oil residue off the throttle blade , and out of the oil line stub etc with carby cleaner.
Check the kerb idle by blocking off the stepper intake and the other end on the manifold, and if necessary adjust to 550-600RPM, withe the grub screw on top of the blade.
Funny I just had this problem with mine after a dyno tune and the tuner later fixed it by dropping settings on my unichip at idle to standard, but mine still occasionally stalls when hot.
I find you have to wait until it goes through all steps, then back up to idle before putting in drive.
Regards Philip A

Will give this a go and see what happens, The stalling is'nt just a problem when starting the car up in fact it revs up from start and drops down like its meant to then the problems start put it in gear sometimes it will die other times it will idle fine, then turn the steering wheel and most times it wants to die.Back the steering out knock it into nutreal and give it a little rev and it comes good again.

[dave]

Try looking at all your spark plug and coil leads for something simple to do. I had a similar idle problem as you describe (stall when load up steering and rough idle etc) and found that one of my spark plug leads was completely corroded at the connection to the distributor cap and others were getting that way.

New rotor button, cap, leads and plugs and it was sweet again.

edit* mine was revving cleanly too, I suspect that at higher revs there was more power available for the coil which could overcome the resistance of the corrosion on the lead. Its an easy check for you though.

Will look at this again but only replaced all the plugs about 3 hours driving on them,The leads are new to with about maybe 20 hours,only the cap is old as the new one i got was stuffed from new the centre contact was not moulded properly but the old cap looks in good shape no craking and the contacts have very little corosion on them.

[advdisco1]

i had my air flow meter replaced(new) 15 months ago, only 14,000kms later same problems again.

[muddydigger]

The 14CUX is prone to stalling as the stepper drops steps out on hot/warm start. It is a 14CUX characteristic.
Sometimes this is caused by oil build up on the throttle blade dropping the "kerb idle", ie the idle with no stepper steps activated.
So clean the oil residue off the throttle blade , and out of the oil line stub etc with carby cleaner.
Check the kerb idle by blocking off the stepper intake and the other end on the manifold, and if necessary adjust to 550-600RPM, withe the grub screw on top of the blade.
Funny I just had this problem with mine after a dyno tune and the tuner later fixed it by dropping settings on my unichip at idle to standard, but mine still occasionally stalls when hot.
I find you have to wait until it goes through all steps, then back up to idle before putting in drive.
Regards Philip A

Will give this a go and see what happens, The stalling is'nt just a problem when starting the car up in fact it revs up from start and drops down like its meant to then the problems start put it in gear sometimes it will die other times it will idle fine, then turn the steering wheel and most times it wants to die.Back the steering out knock it into nutreal and give it a little rev and it comes good again.

Airflow meter or
stepper motor
or sucking air may be even through the rocker cover gaskets. Either way when the car starts it should not rev high then die down, it should start and sit steady at about 750 rpm.

[dave]

Thanks for the advice, geuss i'll just have to start replacing suff till its fixed.

[armbrup]

14CUX is supposed to "rev high then die down"
On each shutdown the stepper winds out to maximum.
On start up the ECU reads the RPM signal and drops steps out until idle stabilises at about 750RPM in neutral on a warm engine.
Aircon on adds one step.
VSS adds one step.
I think cold start adds one step. ( not sure of this but certainly cold start is faster)
Regards Philip A

[6.2troopy]

had the same problem, a new air filter fixed it straight up.

[RRV839]

Make sure you're coolant temperature sensor has a good earth and the connection is clean and tight, i frequiently have to do this on my 3.9 as it reads wrong and throws the idle out all ove rthe place, also you can get what the call an air mass meter cleaner, similar to carby cleaner, but safe to use as if doesnt stuff sensor's. ive use this in mine and it ran alot better and got better fuel economy. AFM, coolant sensor and air filter fuel filter and plugs and leads are the common ones, obviously checking all the disposables like plugs and filters first is the best way to go about it. Also make sure you are getting consistant spark, and when the engine is running does the tacho flicker at all, this can be a sign of an ignition module on its way out i've replaced a few in my LR's and the problems we're usually worse when hot.

[armbrup]

All good stuff except the tacho is driven by the alternator, nothing to do with ign module.
If the tacho flickers the alternator is dying, which could of course also affect idle speed.
On cars other than LRs often the tach is driven by ign.
Regards Philip A

[dave]

I dont have a tacho the engines in a buggy so no idea if it flickers

[dave]

I dont have a tacho the engines in a buggy so no idea if it flickers

[RRV839]

Are you sure about that? I have had the alternator off my car (when i had it rebuilt) and driven it in and out of the garage etc and the tacho worked then, i know there is two differnt types of modules, could this be one of the differences maybe?

[dave]

Are you sure about that? I have had the alternator off my car (when i had it rebuilt) and driven it in and out of the garage etc and the tacho worked then, i know there is two differnt types of modules, could this be one of the differences maybe?

Not sure what your getting at. I have no tacho as the motor is in a buggy and i dont run a tacho. Or where you just getting at the tacho flickering not being directly related to the alternator.

Anyways i borrowed an Airflow meter and stepper motor off a running car today,
1st i tried the stepper motor where there was no real difference.
2nd i added the airflow meter this only made the thing run like shit,put im back in and it would idle smooth again so i swapped my stepper motor back in and again it stayed the same,so again i put the borrowed airflow meter in and the car idled ruff again.
So after all that i have my original airflow meter and stepper motor back in and its idling smoothly.It also dosn't seem to stall when in gear and turning the steering anymore.
I'll take it for a run this weekend and see how it goes.

Im still unsure of what was or is causing the problem , but i guess i have eliminated 2 things
Any other thoughts.....

[RRV839]

yeah sorry off track i was reffering to the alt and tacho

[armbrup]

yeah sorry off track i was reffering to the alt and tacho

Yes I am sure on all 3.5 and 3.9 with v belts anyway.
Haven't really looked at later ones . See if it has a third wire from the alternator which is white AFAIR.

Regards Philip A

[RRV839]

ah, mine is serpentine (late 94) i'll still check the alternator though.

[armbrup]

What sort of steering box and pump do you have?
The 14CUX idle etc is calculated on a standard rover pump load.If you have a bigger one it could be the problem.
In this case the fix would be to just increase the kerb idle a bit to compensate.
The other trickier fix could be to rig a switch to the ECU input for the aircon clutch (assuming you have no aircon) , to trick up the idle when you want to turn the steering while stopped. Falcons have a switch on their steering racks for this.
regard sPhilip A

[dave]

What sort of steering box and pump do you have?
The 14CUX idle etc is calculated on a standard rover pump load.If you have a bigger one it could be the problem.
In this case the fix would be to just increase the kerb idle a bit to compensate.
The other trickier fix could be to rig a switch to the ECU input for the aircon clutch (assuming you have no aircon) , to trick up the idle when you want to turn the steering while stopped. Falcons have a switch on their steering racks for this.
regard sPhilip A

Running a VK commodor pump and a steering orbital valve to a 2.5x8 stroke singal ended ram.
This has been on the car for a good six months prior to the problem arising.
I am running an aircon pump as an air compressor which cycles regualy while runnig due to small air leaks , lockers and air accuated brakes, it dose not seem to afect the idle when it kicks in and out .

I also looked at the TPS not sure how to check it other than unplugging it,when i did this it still idled ok but had a delay when opening the throtle.Pluged it back in and the delay was gone so im geussing thats working fine.
Could the computer be the problem

[advdisco1]

i got my idle fixed the other day and it was the air flow meter again. they put a new one in and all was good. i think the meter is ajustable somewhat cause they set it up to a machine(scope) to test it and adjust it cause it was running to lean.(the old one was running to rich) so i think if you change the meter it could still run lean or rich on idle but it may fix the problem.
i dont know how to adjust it maybe someone else knows

[armbrup]

Have You got a K&N filter on it?

The 14CUX is almost unique in that it does not have a "burn off" phase on shut down.
oil from the filter can foul the MAF wires.
The fix is to clean them with no residue CO2 electronic contact cleaner. The wires are located in a little hole on the left? as you look into the MAF.
At the same time slightly twist the prongs in the connector on the MAF to get the best contact.
Then replace the K&N with a paper filter.
Regards Philip A

[advdisco1]

do you think that the k&n would do damage to the afm. i was told the a uni type filter would be no good(soaked oil) but a k&n type(spray on oil) would be ok

[RRV839]

had a k&n for the last 12month and ive never had an afm problem in my car ever.