intermittent problem with tick over 300 3.9 v8 1996

Hi all
Please help me with this very irritating problem ! I have a1996 3.9 v8 with a distributor with a module in the base and an amplifier next to the coil. Car has always run very well.About a month ago it developed an intermittent tickover problem hunting and events for stalling at rest. The car is auto so you can sometimes save a stall by putting it in neutral.Otherwise it ran very well. Three weeks ago I decided to replace some old parts with quality or or OEM bits. I replaced the coil ,ht leads, distributor cap,rotor arm ,spark plugs, air and oil filter and all oils.The old plugs were a lovely light brown colour. The car now runs very well with incredibly smooth power delivery at all revs and doing about 17 to the gallon But ,after an improvement for a few days, the tickover problem is back. Is there some air or petrol feed that needs cleaning or whatever becausecI do not know what to try next!
Please help if you can
Many thanks
Mussy

Check the crankcase breather and so called "flame trap" isn't blocked also run a bottle of injection cleaner through the system for a start, if there is still a problem u will need to check and may maybe clean the idle control valve and check/set the base idle speed.

Instructions good setting base idle herehttp://www.actproducts.co.uk/2011/lucas-14cux-fuel-injection-system-–-installation-and-diagnostic-notes/
I tend to nip the stepper motor to throttle hose with long nose mole grips rather than fashion bungs.

The 'base idle' is factory set so shouldn't need adjusting, unless it's been interfered with in the past that is.
Even after after 17 years mine has never had the need never been adjusted but then if you don't know the engine history its worth a look at.

Thanks Guys

I have checked the crankcase breather and the plenum entry --both were a bit grubby but clear . I cleaned them out and will see if it has an effect. I have had the car for 15 years -70 of its 80k miles and the tickover has never been adjust ed although I see the allen head is not protected by an anti -fiddle device! I will report on if there is an improvement ,and also try the injector wash. In the meantime ,can you tell me hoe to clean the idle valve? Do i just unscrew the allen head ?

Best

Mussy

Thats all just under screw it, you will need a large spanner, you may/will require a replacement fibre washer.
I removed mine once for a look see and a bit of preventive maintenance but there was nothing to clean so refitted it straight away.

Are you getting mixed up with idle adjustment screw and air bypass valve? Air bypass valve is the small canister bolted to the back of the plenum chamber. Instructions here but quite what all these 10 seconds are for me not know.
Fixing high idle speed problems on Lucas Hotwire Equiped Rovers - Stepper Motor Idle Speed Control | Land Rovers

Check the flexi hose air flow meter to throttle for holes.

Dear cooltide and discool,
Thank you very much for that---I will now check those pointsand report back--I was confusing the idle screw and the by-pass valve. Is there no way of cleaning the idle screw as ,from what little I can see from the MAF/plenum connection -its filthy!

All the best

Mussy

carb cleaner but you don't want to loosen crap and suck it into engine, so its a plenum top off job. If it ain't broke.....

I know I am getting ahead of myself but ,if I need to replace the stepper I see that Rimmers have the oem at £240 and the aftermarket at £70 ---are the aftermarket any good?
best

Probably are. If you haven't got a tachometer, Stick an Allen key in the idle adjustment screw and give it 180 degree turn anti clockwise. Take live off battery and reconnect after 30 seconds to reset ecu. It may be all it needs and you can reverse the procedure if it doesn't sort it out.

Cleaned the internal area on the idle screw so far as I could from the plenum /maf join and its been 4 days and 120 miles and the idle has been fine. Do you think thats the problem solved or is it lulling me into a false sense of security?

Hi all!-----There,s no fool like an old.........! So after talking about it for weeks and trying everything else recommended and that I could think of ,I very nearly ordered a new stepper but took the plenum top off first .Lots of nasty bits of old gasket goo and other rubbish in there but nothing obvious causing the problem so I had a look at the stepper motor .This is housed at the back of the plenum chamber up against the back of the engine bay and only easily accessible when you have taken the plenum top off. --So grabbing the housing with a view to extracting the stepper and replacing it ,I stuck my half inch socket ratchet on it and prepared to heave--only to find all three bolts not even finger tight .! It occurred to me that this would let a lot of air in through the gasket so I applied flange seal wherever appropriate and tightened everything up and its been running fine ever since (about 800 miles) tickover has never been better --rock solid at 700. Trust me to miss the obvious. Thanks again to discool and cooltide who tried very hard to push me in the right direction of airleaks !
Go Well
Mussy