3.9EFi revs dropping too low when drive & reverse selected

Not read all the pages... but I have Rev Drop when in R or D and had the hot stall issue where it would just keep dropping when out and about. This is a 1990 3.9 EFI.
I changed the Stepper/Idle and cleaned inside the chamber.
I also removed the Flame Trap and replaced it + cleaned out all 3 pipes from Flam Trap to T Piece, Pipe to Plenum and smaller pipe in to right side. My T Piece has a brass insert which was clogged and the trap and pipes were well crudded up.
Went through about 1 large can of brake cleaner doing this and sprayed anywhere in plenum I could and cleaned it all up.
Cleaned the pipe from the back of the idle valve which comes round to the back of the plenum as well.

Since then its been fine not changed the idle on the throttle.

Did try and remove the plenum but the allan key bolts are very very tight so did not risk it.

Right then thats my next job then..again. this time Im gonna replace all the hoses, crankcase filter and spark plugs too. As a point I have a hose at the back of the plenum in front of the throttle linkage that goes into the plenum housing. It has a metal "sleeve" this seems very easy to slip off, should it be "air tight" would the system be that sensitive to a loose fitting sleeve?

anyway thanks for the info.....will order the bits and go for new. it all looks original anyway.

right then, checked and cleaned, new stuff on order, however I jhave since discovered that when I remove the vacum hose going into the fuel regulater, it doesnt drop the revs at all and runs perfick!!! Im getting plenty of suction from the hose so that ok. Does this mean shagged fuel regulator or would there be other symptoms. Smells better too when removed, no petrol in exhaust, so maybe the issue was over fuelling from a sticky/broken regulatot.

good find if it works

cox325 said:

right then, checked and cleaned, new stuff on order, however I jhave since discovered that when I remove the vacum hose going into the fuel regulater, it doesnt drop the revs at all and runs perfick!!! Im getting plenty of suction from the hose so that ok. Does this mean shagged fuel regulator or would there be other symptoms. Smells better too when removed, no petrol in exhaust, so maybe the issue was over fuelling from a sticky/broken regulatot.

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Then let us all know because that the last place one would look for a fault.

Ok another update!!! Changed breather. Changed stepper motor old one had sheared leaving thread in hole!! Changed fuel regulator for new. At first everything seemed sorted but when warm after a short run it's back to dropping the revs when going from N or P to D or R. Still no faults on ECUmate. Base idle set although the screw won't go in any further!! Garage seemed stumped. So am I.

cox325 said:

Ok another update!!! Changed breather. Changed stepper motor old one had sheared leaving thread in hole!! Changed fuel regulator for new. At first everything seemed sorted but when warm after a short run it's back to dropping the revs when going from N or P to D or R. Still no faults on ECUmate. Base idle set although the screw won't go in any further!! Garage seemed stumped. So am I.

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Base idle screw in to lower idle speed, screw out/up to raise idle speed. Has been that way around with all mine.
Did ya type that out the right way mate?, as it will stall with screw right in.

when I had a hot running fault I changed everything and it turned out to the tps

im assuming its working as i have 0.34v and a progressive increase in value as throttle is depressed also ECUmate shows 2% throttle postion at idle. I really do wish it was something simple!! She has an MOT on Friday, plus I got a ZF gbox filter for them to do with a gbox oil change. See if that alters it, might even get em to try a base idle reset that I have been doing every time I try something else!!

that oil change may well fook your autobox right up if its not had them at the correct intervals in the past. for your own sake plese read the FAQs on ashcrofts website for the 4hp22 box. It ended up costing me a box rebuild ell before it needed it and on cars this age they may well be scrapped before the box would die a natural death. its about £1500 for a box rebuild and fit btw :doh:

I hope it wont come to that!!! the car has never been offroad yet! but Im building it for that purpose, inspired by mr noisy and green hornet I have to admit. Anyway the service book shows Matford dealer stamps up to 64327 miles in 2006, since its been in cardiff and done 20,000 then I bought it. I got all receipts of service and parts etc, so can only assume its all been regular and showing genuine parts too!!

ok , well read the faqs and be sure bud- its the oil change that can cause them to fail early

I think it was only 14 cu on the sd1

I cant even remember if the op is running 14 cu or 14cux this has been going on so long lol

roger

thanks for the link, very intresting read and is obviously exactly the issue I have, the solution though is more complicated!! None of the parts listed still exist and found it a little hard to follow, especailly the solution!! When my baby comes back from the garage with a new MOT I'll have another look though.........otherwise I'll have to live with it then

what injection system you running? cant remember

the air valves are what they use for air con models which would give the same symptons when the air con kicks in due to the extra load on the engine.

fett said:

what injection system you running? cant remember

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14CUX hotwire etc , no lpg

3.5 efi said:

the air valves are what they use for air con models which would give the same symptons when the air con kicks in due to the extra load on the engine.

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I got air con on mine, so could I just get another/same valve used for that?


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