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Old 01-18-2012, 03:23 PM   #1 (permalink)
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4.0 Disco has idle surge and stumbling issue, very puzzled

My buddy owns the Disco, 97 4.0 with around 140k miles. This problem has never occurred over the years until last week. It would start to idle between 1500 and 3000 rpms. It will surge slowly up and down between them. It also tends to stumble when you drive it which is getting worse and worse.

I pulled it into the shop last week to do a general check of all the usual suspects. We smoked the engine, no vacuum leaks. We took the IAC out to check it. Looked fine but ended up popping the plunger out by accident while cleaning. We replaced it anyways. This did not fix the problem. Checked alternator charge voltage, right at 13.8 and very steady. We swapped another one in just to see and didn't fix it. Cleaned up the MAF, no fix. Disconnected the VSS, didn't fix it. Checked TPS voltage on the scan tool, 0.5v at idle. Everything seems to be spot on. It also does it right on cold start so I am assuming O2 sensors would not cause this in open loop.

The MIL is on with a fuel temperature and a downstream O2 code which they have been in there for years and never had this problem so I am really not wanting to start parts swapping like a hack with these two DTC's.

We unplugged the IAC with it idling at 1500 and it still surges up and down. Very unusual for a stepper motor IAC. This surging must be spark or fuel related and not an idle circuit issue after seeing this.

Any input on what next to look at? I'm thinking possibly a badly worn timing chain or funky crank/cam sensor? I'm running low on ideas. The ECM housing has some corrosion on the inside aluminum bits but the circuit boards are very clean.

My British accent sucks and maybe it knows that I love Jap trucks...I don't know but the solution is evading me
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Last edited by Pietro; 01-18-2012 at 03:24 PM.
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Old 01-19-2012, 05:26 AM   #2 (permalink)
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The ECM housing has some corrosion on the inside aluminum bits but the circuit boards are very clean.
Pull the boards out, scrub them under warm running tap water and dish soap.

Rinse with DI water or alcohol, allow to dry, reassemble, reset adaptive values.

See what you get.
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Old 01-19-2012, 05:33 AM   #3 (permalink)
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For resetting values, is a generic scanner or code reader clearing DTC's reset adaptive learning or does it require a LR Testbook scanner?

Thanks for the help PT
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Old 01-19-2012, 06:22 AM   #4 (permalink)
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For resetting values, is a generic scanner or code reader clearing DTC's reset adaptive learning or does it require a LR Testbook scanner?

Thanks for the help PT
I only have experience with Rover-specific diag computers.
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Old 01-19-2012, 08:14 AM   #5 (permalink)
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We may break down and bring it to the Rovah dealer to get the OEM scanner on it. My OTC doesn't have European software and it won't even connect in generic OBDII mode. I used my better code reader which did connect and read live datastream.

Thank you for the input!
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Old 01-19-2012, 09:42 PM   #6 (permalink)
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Pull the boards out, scrub them under warm running tap water and dish soap.

Rinse with DI water or alcohol, allow to dry, reassemble, reset adaptive values.

See what you get.
OMG!!! That is all!
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Old 01-20-2012, 07:31 AM   #7 (permalink)
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OMG!!! That is all!
I do it all the time KC. Maybe get one in the mail once a month to have the boards cleaned up, adaptive values reset and put into security learn mode.

The only ones I haven't been able to rescue were those where the corrosion traveled up the ribbon cable. I don't have the patience to solder all those tiny little connections.
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Old 01-20-2012, 09:14 AM   #8 (permalink)
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I saw a guy hang a case of beer from his scrotum.
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Old 01-20-2012, 01:17 PM   #9 (permalink)
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There's nothing wrong with what he's doing as long as everything is de-contaminated and dried before voltage is applied again. At the factory, those boards are washed in DI water after soldering, since they use "green" flux (water soluble).
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Old 01-20-2012, 02:03 PM   #10 (permalink)
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Tap water should not be used, nor should dish soap. Distilled water is fine. As the tap and dish soap evaporates, it leaves mineral deposites and othe chemicals that cannot be rinsed off with DI water.

Processes at the factory are done under controlled conditions, not in the shop sink or out in the back with a hose.
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Old 01-20-2012, 04:34 PM   #11 (permalink)
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Tap water should not be used, nor should dish soap. Distilled water is fine. As the tap and dish soap evaporates, it leaves mineral deposites and othe chemicals that cannot be rinsed off with DI water.

Processes at the factory are done under controlled conditions, not in the shop sink or out in the back with a hose.
Yeah, it's so much worse than the salty water and windshield washer fluid that they get exposed to under controlled circumstances.
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Old 01-20-2012, 05:05 PM   #12 (permalink)
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Doctor says to patient, sorry you got your eye poked out witha stick, since the damage is done, do you mind if my retarted son pokes you in the eye with another stick before I stich it back up for you.
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Old 01-21-2012, 07:39 AM   #13 (permalink)
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Doctor says to patient, sorry you got your eye poked out witha stick, since the damage is done, do you mind if my retarted son pokes you in the eye with another stick before I stich it back up for you.
KC, prove you're just ignorant of this process and not stupid.

Once again, a cursory investigation would have taught you that this is an accepted practice.

But, I accept that if "I" say it, you just have to challenge it, regardless of how reasonable my statement may have been.
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Old 01-21-2012, 09:01 AM   #14 (permalink)
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And I quote!!


"In general, there are three general grades of water: tap water, distilled water and deionized (DI) water. In terms of cleaning, neither tap water nor distilled water are sufficiently pure to handle the job as both are contaminated, to greater or lesser degrees, with minerals and organics. So you must jump to DI-water."


"Rinse with deionized or distilled water. Many people prefer to rinse with deionized water over tap water. Regular water will leave deposits that can cause electrical shorts, but deionized water will rinse clean, dry, and leave nothing behind."

Hell, this next guy can't even complete a sentence and he knows better than to use tap water

"In fact, we ourselves can begin cleaning the motherboard, so pay attention to that special washer to buy water, or to use non-conductive second distilled water to ensure clean water without the electrostatic ion. Note that it is best not to use our mineral water drunk (including the much-ion impurities), do not use tap water, such water often weak acid or weak alkaline, susceptible to corrosion circuit boards."


Guess they use DI water cause its more expensive than tap water!

http://www.engineeringlab.com/cleaningbatch.html.

You can dunk a computer in the ocean then clean it and it will "run". But it's not good for it. If we were talking about a board with simple components like resitors and caps, go ahead and puke on it for all I care and it will be fine. But once you start moving up to true computer boards, there are far to many delicate components that have nooks and crannies that you will never be able to rinse the tap water out of.

Just because you CAN do something does not make it right nor does it make it good advice.

I guess I will run over to Intel down the street today and tell them they don't need all that water filtration equipment and they can simply use tap water to rinse all their chips etc. It will save them a bunch of money.
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Old 01-21-2012, 09:35 AM   #15 (permalink)
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KC-you're beating a dead horse here.

If you can pull your head out of your ass long enough and really think about this, you'll realize you are arguing to argue.

The reason the ECUs become compromised is exposure to corrosive salts. Rinsing in tap water and detergent will loosen and remove those deposits. Any remaining salts can then be rinsed with distilled or DI water and consider it done.

If the salty water had a given conductivity, one could assume tap water to be at least ten-fold less, and distilled/DI to be another ten-fold less.

And, as for your internet cut/paste, I found multiple examples of folks suggesting that circuit boards could be run through the freaking dishwasher.

Yet again, something one learned in general chemistry proves the answer.
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Old 01-21-2012, 09:48 AM   #16 (permalink)
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Your advice is wrong period! And it could lead some soccer mom to stick her Land rovers perfectly good comp in the dishwasher because one of her headlights is dead. The things you post on the Internet are read by idiots alike and many can't be bothered by reading things in their intirety. So they jump to conclusions on their jump to conclusions mat and they fuck shit up due to bad advice.

Your advice to use tap water on a crusty nasty board that may be dead already is suitable, but if the board is not truly damaged yet, you may in fact do more harm than good.


Oh and my quotes were for Professionals not 16 year old Ask Jeeves authors.

And dishwasher cleaning is fine when they are supplying the dishwasher from DI water sources which is where this idea originally comes from. Then your ask Jeeves author heard from his brother in law that they use dishwashers at low budget refurbishing houses and runs home to drop his lap top into the load with the casserole dish from last night.
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Old 01-21-2012, 10:23 AM   #17 (permalink)
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Your advice is wrong period!
Clearly that is why it is so effective in returning otherwise dead Land Rovers into operational vehicles.
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Old 01-21-2012, 10:32 AM   #18 (permalink)
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Never said it wouldn't "work".

You just can't help but miss the point can you! Go to fucking Walmart and buy some distilled or DI water plus some denatured alcohol and do it right! Or use some of the pre packaged chemicals in a can that are designed for the job.

By the way, FYI the purer the water the more aggressive of a solvent it becomes. I took chem to!
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Old 01-21-2012, 11:33 AM   #19 (permalink)
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Back at ya KC. Start with warm running tap water and end with the reagent grade water and then the alcohol.

If you didn't take P-chem, none of the earlier stuff matters
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Old 01-21-2012, 04:15 PM   #20 (permalink)
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Oh good god. It is just a simple circuit board. It does not matter...
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Old 01-21-2012, 04:44 PM   #21 (permalink)
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I want to change my name to Jeeves. For sake of soccer moms
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Old 01-21-2012, 05:31 PM   #22 (permalink)
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I want to change my name to Jeeves. For sake of soccer moms
That's why I was having you drive me around in my own truck at CC!
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Old 01-21-2012, 06:26 PM   #23 (permalink)
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I wouldnt mind cleaning some soccer mum's.....
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Old 01-21-2012, 10:09 PM   #24 (permalink)
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I wouldnt mind cleaning some soccer mum's.....
Why is it that when I think of cleaning an English soccer mom, I think of Victoria Beckham
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Old 01-21-2012, 10:44 PM   #25 (permalink)
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Why is it that when I think of cleaning an English soccer mom, I think of Victoria Beckham
maybe you had some meat stuck between your teeth and needed a tooth pic....
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