3.9EFi revs dropping too low when drive & reverse selected

This ones a new one on me...

The wifes 3.9EFi Auto starts and runs fine, smooth too. HOWEVER, occasionally and normally only when the engine is fully warm, if you select D drive or R reverse from either P park or N neutral the revs drop down a little too much. Wife says it has stalled on occasion.
I tried to replicate this today, and indeed it dropped down to a near stall when going from D into R pausing at N. D into R without the pause at N did not cause any issue.
I can understand that the idle/revs are going to drop a little when engaging gear, but the drop seems a little excessive compared to RRC of the past and present.
Only things I've done so far is a basic service (oil,plugs and filters), checked timing (ok) and sprayed intake cleaner on MAF and into plemun.
Codes read and showed that the base idle set too high. So, I've screwed that in and set properly, wierd as it looked like it was nearly completely unscrewed before I screwed it back down to its proper position. I reckon previuos owner may have experienced the same and just thought ****ing about with the base idle would rectify it! dou
Ironically this doesnt seem to have changed any of its running, so I disconnected the battery in the hope that would reset the ECU properly...with no change!
Oh, and I replaced the stepper valve for a clean one

The issue only happens in day to day driving if the driver pauses at the neutral selection if going from D to R.... Personally I'd be happy just to drive around the minor issue, so I've just said to the wife that she just needs to speed up her gear selection!

I'm thinking probably there's gundge in the intake assembly that a cleaner spray can't shift, particularly as the stepper valve I took out was well grottied up!.


Would appreciate any other thoughts and suggestions I may have missed?

check colour of box oil

ah...forgot to add...when we bought it the box fluid was very very low (in fact we bought it at a silly cheap price as the seller said it felt like it was jumping out of gear occasionally...related?)...so I topped it up after buying asap.
Doesn't look too bad tho this could be down to some fresh red stuff being in there diluting the old (too old) stuff??

Or, maybe not having anywhere near enough ATF in there damaged the box??

Why didnt you change the oil rather than top it up?

storm99 said:

Why didnt you change the oil rather than top it up?

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The priority at the time was to see if the occassional 'jumping out of gear' the seller had said was down to there being very little ATF in the box when I looked....luckily for me it appears it was. Messing around with a change would've been a waste of time if I then needed to change the box (which is what I was expecting to do when the wife bought it)
ATF aint that expensive, so I think I'll probably change it as next course of action?

just check it for burnt clutch evidence ,

jamesmartin said:

just check it for burnt clutch evidence ,

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I'm assuming evidence will show itself as black or brown bits in the fluid or general brown discolouration?

cheers for your help James

had the same on my 3.9 joe, before and after a recon box (didnt have it recond for that)

tried everything, so did stu and in the end we put it down to worn/stretched valve gear timing chain etc. it helped getting it timed up well and a base idle re-set (but I think you have probably done that) but it never went away. if it makes you feel any better it never got any worse either and I just got used to it. it only actually stalled about 4 times in 2 years.

You could always cheat and just wind the adjuster on the throttle cable out like k-man did for a year or so but I know it was a bad boy thing to do

fett said:

had the same on my 3.9 joe, before and after a recon box (didnt have it recond for that)

tried everything, so did stu and in the end we put it down to worn/stretched valve gear timing chain etc. it helped getting it timed up well and a base idle re-set (but I think you have probably done that) but it never went away. if it makes you feel any better it never got any worse either and I just got used to it. it only actually stalled about 4 times in 2 years.

You could always cheat and just wind the adjuster on the throttle cable out like k-man did for a year or so but I know it was a bad boy thing to do

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Cheers Fett....I have advanced the timing very very slightly only about a degree, but is was pretty much how it should be, which is why I didnt bother mentioning above.
so did K-man's cable last ok or give up after leaving it under tension?

Joe, if the stepper looked proper grotty I would recommend you take off and clean the plenum and ram housing. Whilst it's all off, check the setting of the throttle disc and make sure that is all clean as well. Then I'm afraid it is the "set base idle" routine. One other thought, stick a strobe on it and watch the timing - does it wander?

I had odd running issues some time back and found timing was going all over the place due to a stretched timing chain.

joe1972 said:

Cheers Fett....I have advanced the timing very very slightly only about a degree, but is was pretty much how it should be, which is why I didnt bother mentioning above.
so did K-man's cable last ok or give up after leaving it under tension?

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Nah it lasted, but his headgaskets gone

setting it up like that will keep recoding a tps fault in the ecu though, I am not sure if that will do any real harm but it will make good reading on ur fault code machine if anything else goes wrong lol

Make sure you do a good read of my posts on changing the autobox oil if you dont know when it was lst done/hasnt been done for too many miles.

Hope you get it sorted mate.

classic kev said:

Joe, if the stepper looked proper grotty I would recommend you take off and clean the plenum and ram housing. Whilst it's all off, check the setting of the throttle disc and make sure that is all clean as well. Then I'm afraid it is the "set base idle" routine. One other thought, stick a strobe on it and watch the timing - does it wander?

I had odd running issues some time back and found timing was going all over the place due to a stretched timing chain.

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Timing was rock steady once the idle speed settled.
Yep, I think a good clean will be on the agenda once the weather gets better n Jacky doesnt need it to get her to work n back instead of slip sliding around in an old rwd merc.
For now I think she'll be just driving around the issue.

cheers chaps

Have you done a base idle reset?
Try a double clean out of the auto box oil drain replace the filter run for 100 miles drain again and refill as it maybe a dead bit of sludge in the torque convertor throwing the base idle out

vougese39 said:

Have you done a base idle reset?
Try a double clean out of the auto box oil drain replace the filter run for 100 miles drain again and refill as it maybe a dead bit of sludge in the torque convertor throwing the base idle out

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yes, base idle spot on.
Yes, as said before, I think changing the box fluid is going to be something I will do. Thinking the fact the level was so low could well be some grot in the system.
cheers for the advise.

read the 4hp22 FAQ on ashcfrofts before you change it joe, it fooked mine right up

It could well be your stepper motor. They are 'fickle' things and can have this effect if they are not seating very well, or indeed if the motor is just shagged. The fact that the air bypass screw has been moved a long way would indicate that the stepper is open a fair bit ... what method did you use to set the base idle?

LOL...this thread seems to be going round in circles!

thanks for the advice folks.
I shall do what I've said I'll do asap.
cheers

fett said:

read the 4hp22 FAQ on ashcfrofts before you change it joe, it fooked mine right up

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I did the change with the bobtail...it worked wonders with that...but I guess I was lucky that time lol

joe, sorry to drag this up again, but I have exactly the same problem since i bought mine, I have recently done the base idle 100 times!, engine oil changed and stripped plenum to do the rocker gaskets cleaned reassembled etc. new stepper motor,drop in revs still there, approx 300 revs, i put into N rev up, then into drive. I have found to up the idle to 1000 gets rid, but i think its just hiding an isse.

did you resolve yours?