IACV troubleshooting questions - Defender Source
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  #1  
Old February 7th, 2011, 11:54 AM
msggunny
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Richard
08 D3, 04 D2, 77 SIII
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IACV troubleshooting questions

Ok, its on a D1 but it should be the same thing on a 97 D90 with the exception of it having an auto box.

I posted this on another board and i decided to use the "shotgun" approach to see what kind of responses i get. Thanks in advance.

The issue with my IACV has gotten worse. It now kills the engine when i idle the engine while its moving, even a little bit. See below for a better explanation.

I unplugged the IACV and it is doing almost the same thing, almost like the computer isn't "sensing" the IACV. The only change was that after i unplugged it, the truck wouldn't die out when i idled it while it was moving.

This leads me to believe that there is another issue besides the ones i am looking at, namely the VSS. The IACV will do its "check" when i have it out of the manifold and plugged in, the plunger will go out and then back in to set the idle position.

Any ideas as to why it would run the same with it disconnected as it does when its connected?

Anyone know of anyone in the NE area that can reset a ECU's adaptive values? I would send it out and drive the series but i dont have a heater in it and its snowed in....

Thanks

Quick historical update of the issue from an older post:

97 D1 5 speed 102k miles.

New IACV so it shouldn't be that.

I am having a hard time figuring this one out (not really hard since i'm dumb)

After the engine is warmed up and she is has been run a bit the idle will do weird things when i go to neutral, either by putting the clutch in or pulling the shifter out of gear.

It falls to normal idle rpm, bumps around and then drops to almost nothing, some times reading 0 rpm on the tach but my scan gauge rpm reads 300 - 400 rpm does this a few times and then settles down to normal idle rpm.

batt light and sometimes the oil light comes on because of the low rpm.

Its the worst when i coast into a stop.

if i down shift as much as possible until i come to a stop it seems to make it recover faster but still falls on its face a bit.

After it recovers it idles fine, i have tried revving the engine at a stop and it goes to normal idle just fine.

I am inclined to suspect it may have something to do with the VSS. Again, it only does it when the vehicle is moving and not at a stop.

it did something similar in Virginia this summer, part of the issue was a bad IACV and i replaced it and just replaced that one a month ago.

My VSS appears to be working fine, although when i first got it 30K ago it would do the "drop to 0mph while your driving" and "act like you hit the electronic governor at speed" things but appeared to fix its self (which is bull **** i am sure)

Any input would be appreciated, I dont want to just thrown a VSS at it and keep my fingers crossed.

Thanks.
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  #2  
Old February 7th, 2011, 12:09 PM
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Check base idle.
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  #3  
Old February 7th, 2011, 12:19 PM
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James Pierce Jr.
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My money's on the VSS.

Have u tried unplugging it to see if that makes a difference?
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  #4  
Old February 11th, 2011, 07:57 AM
msggunny
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I replaced the VSS and it did nothing. Guess its time to start throwing parts at it. TPS is next.
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  #5  
Old February 11th, 2011, 08:46 AM
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James Pierce
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James Pierce Jr.
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Well I lost that bet!

Holly cow now you sound like my dad His motto is "when in doubt swap it". There are enough parts swappers out there lets try to diagnose the problem first. I remember when I picked up my 90 in Indiana it was running ruff above 1500 rpms so we took it to a local mechanic who wanted to start replacing stuff and get it back to what he called a "base". At that point I knew we were in trouble. He no more knew how do diagnose the problem than the guy behind the counter at Pep Boys.

Some problems are hard to diagnose online but surely with all the knowledge floating around on this board someone can steer you in the right direction. (obviously not me)

A few questions to clarify my understanding of the facts and help get everyone thinking:

It starts and idles fine while sitting still park?
It tries to die but recovers when rolling at any speed without your foot on the gas?
I assume there are no codes and the check engine light is not on?
You've replaced the IACV and VSS.
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  #6  
Old February 12th, 2011, 08:55 AM
msggunny
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Richard
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Quote:
Originally Posted by jamespierce View Post

A few questions to clarify my understanding of the facts and help get everyone thinking:

It starts and idles fine while sitting still park? Correct, although now its starting to bump around a bit, it starts up fine when cold and idles around 900rpm but after running for a bit and then trying to restart it sometimes wont idle at all and die. It is quickly remedied by tapping the throttle when it "starts" and then it will idle normally

It tries to die but recovers when rolling at any speed without your foot on the gas? Correct, it will fall on its face when coasting in to a stop when i take it out of gear, it was recovering on its own but now its dying all together 50% of the time
I assume there are no codes and the check engine light is not on? Yup, no codes
You've replaced the IACV and VSS.
2 IACV's, new VSS and a TPS will go in if the one PT sent me gets here today
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  #7  
Old February 13th, 2011, 04:40 PM
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Dave Johnson
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Are you on the original alternator?...long shot, but there is a long history of crazy symptoms from a failing alternator on the 3.9s..many times causing erratic idling, loss of power under load or during transition...interference with spark...
Also, had you or anyone done anything recently (maintenance, cleanup, etc.)?? I once mistakenly swapped the #1 injector connector with the connector for the one of the nearby temp sensors - fit perfectly...also created a myriad of idling/power issues that varied if the motor was hot/warm/cold...just 2 suggestions before you start ordering up a slew of parts...
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  #8  
Old February 15th, 2011, 09:29 PM
msggunny
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Richard
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New update.

After replacing the TPS and VSS and having no luck with that, i unplugged the VSS and drove it around today.

No issues, runs just fine.

Either the new VSS is bad, or the VSS isnt talking to the ECU in the correct language once it gets warmed up. Or something completely different all together.

Either way it runs fine, i just use my GPS for speed and will get the ECU out to get checked once i get my SIII back on the road.
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