High idle problem MAF ? TPS? other? - Defender Source
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  #1  
Old October 30th, 2006, 03:22 PM
MonLand
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Loic Fabro
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High idle problem MAF ? TPS? other?

Hi,

Here are the symptoms I have on my 1995 3.9L D90:
- when I start the truck, idle is around 1000 rpms (which seems ok for a cold engine)
- As the truck warms up, the idle goes up. It will reach about 1600~1700 rpms.
- From time to time, the idle will oscillate between 1200 and 1800 rpms (either at full stop or if I release the clutch/coast at 30-40 mph). [fast oscillation 1200->1800->1200]. This seems to happen after the truck ran for a while.

From what I understand, when the engine is warm, the ECU work in closed loop (i.e. using more and more of the information sent by the sensors). So it seems to be related to sensor stuff not getting properly to the ECU.

Now this all happened after I replaced the valley gasket (i.e. took the plenum out). When I remove the plenum, I also spayed some carbon cleaner/disolver into the plenum. I think that was a mistake as it is fairly probable that some of the cleaner+carbon went into the MAF / TPS / side....
I am pretty sure there are no vacum leak (but then... not even sure how to verify that completely).
Based on what I read in other message, a few potential culpirit:
- the ECU might need to get reset (unplugged for 5 minutes)
- the TPS might need to be cleaned (or replaced)
- the MAF might need to be cleaned (or replaced)
- fuel pressure regulator

What I could not find anyway yet is a way to test the TPS or the MAF. You folks seem to be swapping those out for good (better?) one and look for improvement. Is there a more "scientific" way of testing both? :-) [Probably with a voltmeter or a ohmmeter]

What do you guys think?

I would typically not use my D90 to go to work, but I am losing a lot of power steering oil on the disco.... so now I have to fix that problem! :-)

Thanks,
MonLand.
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  #2  
Old October 30th, 2006, 04:27 PM
btate
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Bryan Tate
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There have been alot of recent post regarding this issue. I would read up on those.

I have chimmed in several times on this one, as I had the same problem.
(replaced, MAF, O2 sensors, distrib and module, Stepper motor, tps, engine flush, etc)

Mine was MAF, got a used one and it fixed the problem. I worried about vacuum leak also on my truck, seems a likely culprit for yours with the recent work.

It does take a good while for the computer to sort itself out, if you have disconnected it, or replaced something it reads....
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  #3  
Old October 30th, 2006, 04:42 PM
MonLand
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Any specific thread in mind? I'll do a search with your name in it! :-)

Follow-up Post:

Before I forget: there are no codes raised by the ECU, no check engine light. And as expected, disconnecting the MAF "fixes" the problem (and the check engine light comes on! ;-) ).
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I have an ex MoD and an ex wife. The two no longer conflict with each other.
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1996 Discovery NAS
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  #4  
Old October 30th, 2006, 05:35 PM
btate
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Bryan Tate
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I didn't have codes either....shall I saw. I had codes only when I disconnected things.
Well, there was a code 23 if I remember correctly, but it hit or miss with it.
I enventually took it the LR dealer, a great mechanic there reset base idle and got it purring like a kitten.

Does it stall out at idle?

Do an "advanced" search in "Looking for help" use the word "Idle" and "search title only"
That should give you enough reading for the night.....
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  #5  
Old October 30th, 2006, 06:48 PM
MonLand
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Loic Fabro
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Cool Got code! (48 - stepper motor)

Quick update, On the way bad tonight, I did get the Check Engine light. I have a code 48 now.


=====
Code 48 - Stepper motor
check base idle speed- see setting procedure. Refer to tests 15 and 16 of continuity test procedure. Check road speed sensor- refer to test 25 of continuity test procedure.
=====

So I guess I'm going to do those tests.... I only have the 1993 110 Workshop manual, so I hope to find them there.

=========
Additional information: http://www.robisonservice.com/servic...er_trouble.asp
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I have an ex MoD and an ex wife. The two no longer conflict with each other.
Quote:
it is not hoarding it is selective collecting
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MonLand
1995 D90 NAS
1996 Discovery NAS
2006 LR3 NAS (hers, but comfy! :) )
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  #6  
Old October 30th, 2006, 08:06 PM
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Tim Brown
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Might be some good info in here for you.

http://www.defendersource.com/forum/...hlight=code+48
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  #7  
Old October 31st, 2006, 05:07 PM
MonLand
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Quote:
Originally Posted by devinchi
Might be some good info in here for you.

http://www.defendersource.com/forum/...hlight=code+48
It does contain a ton of great information. I will also bookmark the url (http://www.rangie.com/articles_topic...at=6&subCat=26). All the tests are in there! :-)
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I have an ex MoD and an ex wife. The two no longer conflict with each other.
Quote:
it is not hoarding it is selective collecting
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1996 Discovery NAS
2006 LR3 NAS (hers, but comfy! :) )
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  #8  
Old October 31st, 2006, 05:30 PM
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Tim Brown
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Let us know what you find out, I am still dealing with my issues with this code.
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  #9  
Old October 31st, 2006, 06:18 PM
MonLand
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Quote:
Originally Posted by devinchi
Let us know what you find out, I am still dealing with my issues with this code.
Because I also took the T-Case out, I was also thinking that maybe there road speed sensor might have some issues. But I'll definitely keep you all posted!

Last night I cleaned the Stepper Motor (aka Air Bypass Valve). It did not look dirty. The thing it is screwed on those does not seem very "clean" (i.e. the surface it stepper motor will hit is not smooth), so I hope we are not looking for a 100% closure there.
I verified that the Throttle Potentiometer was working (no dead spot), but I did not check the exact values.
Because I left everything in pieces, I don't know if cleaning was enough.....
After reading how the MAF works, I am probably also going to try to clean it a little (seems like dust could get in there somehow?). I do know that the big duct that went from the MAF to the throttle body was not correctly fitted, so when I reinstalled it, I made sure everything was nice tied and clean.... maybe that's the problem..... I will try to disconnect the ECU also for 5 minutes and see if resetting it will help (or not).

I just can't drive it at idle 1600 rpm.... In stop and go traffic, I'll kill the clutch in no time. On the bright side, that gave me more motivation to fix the power steering of the disco! ;-)
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I have an ex MoD and an ex wife. The two no longer conflict with each other.
Quote:
it is not hoarding it is selective collecting
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1995 D90 NAS
1996 Discovery NAS
2006 LR3 NAS (hers, but comfy! :) )
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  #10  
Old November 2nd, 2006, 12:42 PM
MonLand
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Still no progress

It looks like I need help..... :-( Well I guess if I get help, then it's not that bad! :-)

Warm engine, RPM is still in the 1600~1800 range.

I cleaned the Airflow Valve thingy, remove its support, cleaned it as well.
I verified that vaccum is working getting to that same support/into the plenum (when the tube is removed, then RPMs go higher). It's definitely getting too much air..... Any idea if/how I can verify that the Airflow Bypass Valve (Stepper motor) actually works? I measured 50 Ohms (up to the Engine ECU) on both sides, so unless the ECU is not triggering it to close, then I would assume it works.

On "normal" operations, I don't get any error code.
The "road sensor" seems to work (when I unplug it, the truck drives weird/lacks some power/knocks a little).
I tried to unplug the large pipe/create a leak at the output of the MAF/input of the intake, and that does indeed reduce the engine RPM. But the engine might be getting too much gasoline (???? How would I know?). I actually wonder if there wasn't a leak in the past (when I re-installed it, I made sure there was no leak). If I create a too-big of a leak, then I get the 48-stepper motor error (which seems normal as the ECU probably has issues regulating the engine.
I looked at the idle screw adjustment, and it is already screwed to the maximum possible. If I unscrew it, this raises the RPMs even more. I don't know if this is normal or not. I did not see this in the workshop manual.

Any other vaccum line I might have overlooked that would be of interest?
When I removed the plenum, I unplugged the gas rail. Based on what I saw (return goes back to the tank), I assume that nothing needed to be purged, right?

What do you guys think?
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Quote:
I have an ex MoD and an ex wife. The two no longer conflict with each other.
Quote:
it is not hoarding it is selective collecting
---
MonLand
1995 D90 NAS
1996 Discovery NAS
2006 LR3 NAS (hers, but comfy! :) )
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  #11  
Old November 3rd, 2006, 11:00 AM
MonLand
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I was thinking:
- if the RPMs go up after the engine warms up, this might mean that the ECU does not think that the engine is warm, right?
- In that case: it is still in open-loop (probably) and likely to send too much fuel (and less air). Does that sound possible?

=> I should probably check the output of:
* Coolant temp sensor (I assume the ECU does not care about the oil temperature in handling the engine)
* fuel sensor

I unplugged both... not sure if anything could have gone wrong replugging them.... maybe I switch 12V and signal? I would think it is a thermistor, not a funky sensor, but I'll check anyway.

BTW, I had unplugged the ECU for an entire 24Hrs thinking that maybe this would help it reset its adaptive capabilities and restart from scratch.... Tried to restart last night, no change, idle rpm go up as the engine warms up.
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Quote:
I have an ex MoD and an ex wife. The two no longer conflict with each other.
Quote:
it is not hoarding it is selective collecting
---
MonLand
1995 D90 NAS
1996 Discovery NAS
2006 LR3 NAS (hers, but comfy! :) )
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  #12  
Old November 7th, 2006, 12:58 PM
MonLand
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Loic Fabro
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Quick update on this issue: It's fixed! :-)
Last Friday, I went to a NOVA happy hour where I meet a bunch of people (sorry guys.... really bad with names..... Ken, Eric, Tony and Bryan?). Anyway, Tony invited me to come on Saturday as he was wrenching. When I showed up (again.... really really bad with names.....) two other D90 owners were there as well installing a newly purchased NAS Hardtop. Anyway, the plan was to start swapping out parts until one would fix the problem. 5 minutes later, the stepper motor was swapped with a Buick replacement and the engine was running perfect! :-) THANKS!!!!!!

I did some more digging since Saturday: AB stepper motor: $180; Builck replacement (or equivalent): $40....
So, the morale is that even is the resistance of the stepper motor is fine (in my case 60 Ohms), it does not mean it is not stuck (in my case, stuck open).....

For those of you who are suspecting a problem with the stepper motor, here are the ones you might see when the motor is stuck open:
- starting idle around 1000 rpms, raising to about 1600~1800 rpms as the engine gets warmed
- when driving it, if you depress the clutch (i.e. no gear engaged), the rpms will oscilate 1000-1600.
- the OEM stepper motor is very expensive and a cheaper unit can be swapped in (no splicing or anything like that).

HTH someone else!
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I have an ex MoD and an ex wife. The two no longer conflict with each other.
Quote:
it is not hoarding it is selective collecting
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MonLand
1995 D90 NAS
1996 Discovery NAS
2006 LR3 NAS (hers, but comfy! :) )
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  #13  
Old November 7th, 2006, 01:18 PM
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One caveat: that Buick part has an adjustable Pintle -- you need to get it close to spec before you install it.

Glad it all worked out!
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  #14  
Old November 7th, 2006, 04:13 PM
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Quote:
Originally Posted by MonLand
Quick update on this issue: It's fixed! :-)
Last Friday, I went to a NOVA happy hour where I meet a bunch of people (sorry guys.... really bad with names..... Ken, Eric, Tony and Bryan?). Anyway, Tony invited me to come on Saturday as he was wrenching. When I showed up (again.... really really bad with names.....) two other D90 owners were there as well installing a newly purchased NAS Hardtop. Anyway, the plan was to start swapping out parts until one would fix the problem. 5 minutes later, the stepper motor was swapped with a Buick replacement and the engine was running perfect! :-) THANKS!!!!!!

I did some more digging since Saturday: AB stepper motor: $180; Builck replacement (or equivalent): $40....
So, the morale is that even is the resistance of the stepper motor is fine (in my case 60 Ohms), it does not mean it is not stuck (in my case, stuck open).....

For those of you who are suspecting a problem with the stepper motor, here are the ones you might see when the motor is stuck open:
- starting idle around 1000 rpms, raising to about 1600~1800 rpms as the engine gets warmed
- when driving it, if you depress the clutch (i.e. no gear engaged), the rpms will oscilate 1000-1600.
- the OEM stepper motor is very expensive and a cheaper unit can be swapped in (no splicing or anything like that).

HTH someone else!

Do you have a part number for the Buick part?
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  #15  
Old November 7th, 2006, 04:49 PM
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whats an adjustable pintle??? how is it adjusted?
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  #16  
Old November 7th, 2006, 05:11 PM
MonLand
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Quote:
Originally Posted by rover4x4
whats an adjustable pintle??? how is it adjusted?
The thing that sticks out and that has the spring around it. You can turn the pintle and screw (or unscrew) it for it to be longer/shorter to begin with.

Part number? Don't know what I got but the part reference list (http://www.defendersource.com/tech/part_sub.html) gives two:
NAPA 2-1738
AC Delco 25527077

I do know that I read other post about other part numbers (see http://www.jpurnell.com/RR/repairs/A...ss%20Valve.htm for example; use Google for other references! ;-) ).
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I have an ex MoD and an ex wife. The two no longer conflict with each other.
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it is not hoarding it is selective collecting
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  #17  
Old November 7th, 2006, 06:19 PM
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Thanks Loic
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  #18  
Old December 21st, 2006, 09:49 AM
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maybe ill bring this thread back to life. Lets see, 3.9 57k miles runs good etc. etc. All the little vacum hoses look good Ive cleaned the stepper a while back had it hooked up to the computer (rovacom) and it gave a good report. But even since then it will idle high in the mornings to be expected, but even once it comes up to temp and I have been driving it for a while It wont idle down like it should (~750 RPMS) It will idle around 1200 1300 then idle down after a few seconds, could the stepper motor be getting stuck? Any thoughts... o yeah NEVER any codes and consistant 15/16 to the gallon
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  #19  
Old December 23rd, 2006, 11:18 AM
MonLand
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If your stepper was bad the same way mine was, when you are driving (and the engine is hot) around 30 or 40 mph, depress the clutch, leave the skinny pedal along (i.e. no gear engaged _but_ the road sensor will be sending the right info the ECU), if your rpm jump between let's say 700 and 1500 rpm, then your stepper is stuck.
Mine was perfect from the "testing" point of view, no code (well.... except when I unplugged it engine running! ;-) ), the ohm value was perfect (can't remember what the value should be). This is what led me to beleave it was fine until it was swapped for a "really working" one.....
Having said that, did you check/clean the flame trap? Seems that this also could cause the same symptom you are experiencing.
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I have an ex MoD and an ex wife. The two no longer conflict with each other.
Quote:
it is not hoarding it is selective collecting
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1996 Discovery NAS
2006 LR3 NAS (hers, but comfy! :) )
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  #20  
Old January 8th, 2007, 09:44 AM
MonLand
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Any update? Is the problem fixed? If yes, then what was it and what was the resolution?
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I have an ex MoD and an ex wife. The two no longer conflict with each other.
Quote:
it is not hoarding it is selective collecting
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1995 D90 NAS
1996 Discovery NAS
2006 LR3 NAS (hers, but comfy! :) )
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