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  #1  
Old January 28th, 2016, 05:27 PM
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Stalling on stop - rough running

Hello - I have a 1994 D90 ST, about 95,000 miles. Recently the CEL light came on and it is running rough. Like its mis-firing...? When I come to a stop the idle dips very low and sometimes will stall.

I realize how hard it is to diagnose something this random but are there any common issues or suggestions on where to start? I was going to replace the cap, rotor, plugs and wires.

Will an OBD1 reader help and pull codes like an OBD2? Any recommendations on a suitable reader?

Thanks in advance!
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  #2  
Old January 28th, 2016, 05:33 PM
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Quote:
Originally Posted by gmuiter View Post
Hello - I have a 1994 D90 ST, about 95,000 miles. Recently the CEL light came on and it is running rough. Like its mis-firing...? When I come to a stop the idle dips very low and sometimes will stall. I realize how hard it is to diagnose something this random but are there any common issues or suggestions on where to start? I was going to replace the cap, rotor, plugs and wires. Thoughts? Thanks in advance!
is read the codes before anything else.

Might be an oxygen/co2 sensor. Might be an idle control valve or a throttle position sensor.
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  #3  
Old January 28th, 2016, 05:33 PM
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May try cleaning (brake clean) the idle air control valve.
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  #4  
Old January 28th, 2016, 05:35 PM
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stepper motor! ecu uses stepper to control idle air when throttle closed.. and next to throttle plate, theres a bypass channel for air to get to stepper. it can get clogged with gunk and oxygen starve your idle. clean it out with carb cleaner using straw in channel.
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  #5  
Old January 28th, 2016, 05:52 PM
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Also worth mentioning the vehicle speed sensor (VSS). It's been covered on here before.

Any speedometer issues lately?
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  #6  
Old January 28th, 2016, 06:12 PM
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Quote:
Originally Posted by Overlander View Post
stepper motor! ecu uses stepper to control idle air when throttle closed.. and next to throttle plate, theres a bypass channel for air to get to stepper. it can get clogged with gunk and oxygen starve your idle. clean it out with carb cleaner using straw in channel.

Not sure I did it correctly but I unplugged it, unscrewed it and removed. I saw a pin-hole at the very end of the inside of the stepper. I sprayed a bunch of carb cleaner in and on it a couple times. I replaced, started but to no avail. Still running rough and the CEL remains on.

I saw other users simply replacing that part as it appears to be inexpensive. Perhaps I try chasing that.

Also - thanks for the clue on this item as I found another thread here on the Stepper and stalling issues.
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  #7  
Old January 28th, 2016, 06:21 PM
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Quote:
Originally Posted by sherpamike View Post
Also worth mentioning the vehicle speed sensor (VSS). It's been covered on here before.

Any speedometer issues lately?


No speedo issues.
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  #8  
Old January 28th, 2016, 08:25 PM
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I have a 1994 D90 as well and basically had the same problem. For that problem I read the code and changed the Throttle Positioning Switch (TPS) and the problem never repeated. I'd try that route before going to far.

But agree with advice, get codes if your code reader isn't working. My 94 code reader in the footwell still works after all these years.

------ Follow up post added January 28th, 2016 08:26 PM ------

I also had an issue with my stepper which I replaced but in that scenario the opposite seemed to be happening. Mine was stuck at a very high idled from time to time (like 2k rpm) and then would run horribly.
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  #9  
Old January 28th, 2016, 08:28 PM
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I agree with the group- TPS, stepper motor, or potentially a ground issue. Have you installed any new things like lights, lockers, or accessories lately?

My '94 had a ground issue having to do with a shotty air locker install, but behaved similar.

Good luck,

Jay
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  #10  
Old January 28th, 2016, 08:29 PM
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Quote:
Originally Posted by wmatos1001 View Post
I have a 1994 D90 as well and basically had the same problem. For that problem I read the code and changed the Throttle Positioning Switch (TPS) and the problem never repeated. I'd try that route before going to far. But agree with advice, get codes if your code reader isn't working. My 94 code reader in the footwell still works after all these years. ------ Follow up post added January 28th, 2016 08:26 PM ------ I also had an issue with my stepper which I replaced but in that scenario the opposite seemed to be happening. Mine was stuck at a very high idled from time to time (like 2k rpm) and then would run horribly.
This was my experience as well. You can test the TPS. Usually they end up with dead spots.
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  #11  
Old January 28th, 2016, 08:46 PM
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Quote:
Originally Posted by gmuiter View Post

Not sure I did it correctly but I unplugged it, unscrewed it and removed. I saw a pin-hole at the very end of the inside of the stepper. I sprayed a bunch of carb cleaner in and on it a couple times. I replaced, started but to no avail. Still running rough and the CEL remains on.

I saw other users simply replacing that part as it appears to be inexpensive. Perhaps I try chasing that.

Also - thanks for the clue on this item as I found another thread here on the Stepper and stalling issues.
the idle air bypass port is at the throttle/choke plate on opposite (driver side) of engine in the plenum. stepper is on passenger side. take off maf and intake hose. you can see the small straw size hole in the plenum where the choke plate is closed. thats where you clean.
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  #12  
Old January 29th, 2016, 01:07 PM
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May be a funny fix but see if you have any holes in the tub from the MAF to the throttle body. Though this may not affect at idle as it is more the stepper motor issue....or possibly you could see any vacuum leaks to the booster or to the dist.
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  #13  
Old January 29th, 2016, 02:06 PM
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The should be a fault code display that will tell you what the fault is. Mine is under my passenger seat and gives a number for the fault code when the key is on.
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  #14  
Old January 29th, 2016, 04:06 PM
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Bingo another CEL 45... Look for my other post from earlier this week in emissions passing... The rough running happens when the o2 sensor fault comes on, it defaults to the bar fuel map and basically runs rough(er).. Also check all the stuff I already posted before you buy an o2 sensor, takes 20 min or so.. Stalling CAN but not always be the idle sensor already mentioned. They are pretty simple and I'm my Opinion rarely are the root cause, but can mask the symptoms.


Reposting here too.. We need a CEL article or 2





95 Disco uses the same engine management ECU, so should not be the issue (both are 3.9 engines, distributors, etc.. same as the Range Rover for that year).

couple of things to check for a CEL 45.
1) Damage to the O2 sensor body - if it looks beat up replace it - your drive shaft has hit it.
2) loose O2 sensor in the pipe.. 17mm wrench and check for tightness
3) loose at the engine side Plug - make sure it clicks in there good - if you can easy pull it out without squeezing the side clips - make sure the plug is seated all the way and does not come out - mine did this today basically a worn plastic plug - you can zip tie it together.
4) then Replace the O2

Do you know how to reset the codes on it?
1) open the passenger side cubby
2) locate the serial plug (its white with 4 pins - and is 2 pieces connected together. - just kinda hanging out near the ECU.. see picture attached )
3) ignition on (do not start the truck)
4) disconnect plug - wait 5 - 10 seconds - then reconnect.
5) turn off ignition - wait for the computer relay to drop out - you will hear a "Click"
6) turn ignition on (not started again) and check for codes again.. if none are present - then your reset, if there is another one it will now appear - Always do this if you see a CEL 44 - b/c there is usually a CEL 45 right behind it.

Other things that i have found cause CEL 45's
1) Corroded spark plug lead on the distributor - pull them one at a time and check - if you find some replace leads and Distributor cap.
2) leaking main hose (the big one from the MAF to the intake on the top of the engine.
3) Ignition amplifier
4) Coil (usually manifests as CEL 44 and $% with poor running then total cut out)
5) worn plug wires arcing on one cylinder (Passenger side in the case of CEL 45) - dumps fuel into the exhaust and causes backfires
6) exhaust leak Before the O2 sensor - where the header joins the exhaust down pipe.

... some others but those are the main ones that are easy to fix.

Serial Plug picture
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  #15  
Old January 29th, 2016, 04:23 PM
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A 45 code will not make the vehicle run poorly. If it did I would do something about the code 45 fault I have been driving around on for the last 8 months. It means the LH o2 sensor is not sending signal.
Look for bad vacuum hoses first.
Could be a bad ignition amp module.
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  #16  
Old January 29th, 2016, 04:31 PM
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Mine goes from purring to not happy when the CEL comes on..

It's easy to feel the difference.. May be what he is experiencing.. Dunno.

YMMV..

The CEL needs to be solved before moving further
Again IMHO..
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  #17  
Old February 1st, 2016, 08:19 PM
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Quote:
Originally Posted by Overlander View Post
the idle air bypass port is at the throttle/choke plate on opposite (driver side) of engine in the plenum. stepper is on passenger side. take off maf and intake hose. you can see the small straw size hole in the plenum where the choke plate is closed. thats where you clean.

Ok - new Stepper sadly did not fix the situation. Will check the Idle Air Bypass Port next. For those of you who might need the Stepper, here are some pics from my new one, Pep Boys.
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  #18  
Old February 1st, 2016, 08:29 PM
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Have you installed any accessories lately(lights, lockers, CB, stereo)? If it isn't the IACV it's starting to sound like a potential ground issue.
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  #19  
Old February 1st, 2016, 09:07 PM
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Originally Posted by genie90 View Post
Have you installed any accessories lately(lights, lockers, CB, stereo)? If it isn't the IACV it's starting to sound like a potential ground issue.
Negative. There is nothing I installed that wasn't already there. There are ARB lockers and a Winch in place but to my knowledge, are working ok.

IACV is next - will report back the next chance I get to get in to it.
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  #20  
Old February 1st, 2016, 10:33 PM
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Originally Posted by gmuiter View Post
Negative. There is nothing I installed that wasn't already there. There are ARB lockers and a Winch in place but to my knowledge, are working ok.

IACV is next - will report back the next chance I get to get in to it.
Isn't the Idle Air Control Valve what you just tried replacing? Or did I miss understand.
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