Idle speed

[Donjames911]

Just bought a '97 Disco and drove it back from Atlanta to Tennessee, about 300 miles. No problems except I noticed accelleration lag at speed, and the cruise didn't work. When I investigated, I noticed that the vacuum hoses at the tee fitting at the LR of the engine compartment were severly cracked/broken. I cut off the defective ends and re-connected them, but now the engine idles at about 1750 RPM. The manual says it's electronically controlled. Any advice

 

[joey]

Mileage?

I would start with the basics, a full tune up with champion plugs, wire, air filter, clean the MAF sensor, clean the throttle body, change oil.

Then we can see what is up.

 

[Chongo]

Idle speed

Just bought a '97 Disco and drove it back from Atlanta to Tennessee, about 300 miles. No problems except I noticed accelleration lag at speed, and the cruise didn't work. When I investigated, I noticed that the vacuum hoses at the tee fitting at the LR of the engine compartment were severly cracked/broken. I cut off the defective ends and re-connected them, but now the engine idles at about 1750 RPM. The manual says it's electronically controlled. Any advice


Hello;
To start off with most, but not all, cruise control issues are related to the so called vacuum hoses as defined by automotive society lingo.
The truth is there is no such thing as vacuum in the laws of physics, it is a slang term used by our forefathers grandfathered into our language today, and has no scientific meaning. What actually happens is what is called pressure differentials. We live on earth which has 14.7 lbs per sq. in. when the piston in the engine travels away from the cylinder head and reaches bottom dead center, end of the intake ******, around 10 psi will be removed from the combustion chamber leaving the cylinder pressure at around 5 psi depending on the efficiency of the air intake system and the flow of the exhaust, compression ratio and air density. This creates the pressure differentials to exist. Now 14.7 psi outside of the engine pushes air into the 5 psi combustion chamber to tries to neutralize the two. This is how the cylinders fill with air and fuel. This should put an end to the myth that air is sucked into the engine, because it is not, it is pushed. { Now all of these equations are exponential, and not linear so the math involved to calculate these requires the use of algebra and calculus and was created by a math called differential equations. And If you’d like to know the formulas, please send me a private message and I will send it to you.}
With this knowledge now let’s apply it to your land rover’s problem of a high idle and throttle response. Several things will cause high idle, and can also be related to throttle response as well.

1: One is excessive non metered air getting into the intake. This is caused by either a bad signal from the maf sensor to the processor, or ( slang terminology ), vacuum leak, or a stuck iac ( intake air control ), control valve. This will give an O2 sensor a faulty reading, (lean), and in a processors closed loop mode richen the air fuel ratio.

2: Stuck, or improperly adjusted Linkage from the gas pedal to the air intake baffle / butterfly, but this will not cause a poor throttle response.


3: Faulty or misadjusted throttle position sensor.


4: faulty O2 sensors can cause high idle, but not to 1750 rpm, The
processor will run in open loop before that happens, and has some, but
very little affect on throttle response.


5: Crankshaft position sensor.

6: processor, but rare


There are more possibilities, however With the engine running at 1750 there is a fair chance of a vacuum leak, but in any case, this is out of the processors running parameters, and you should have a check engine light lit on the instrument panel regardless. Bad plugs and plug wires won’t cause a 1750 rpm high idle. Before you do anything to the vehicle, lets get the trouble codes read and post the results back on this site for further evaluation, so we can provide more accurate and better help to you. Without the trouble codes, it’s anyone’s guess.

Get back with us on the trouble codes, most parts stores have a code reader that will read codes for the emissions systems only, and it’s usually free, or at a nominal charge.


Checking plug wires:



Testing plug wires

Testing plug wires


Some of you have asked me this question in the past and have asked me to post this, and I thought It could be helpful................


Testing plug wires: First of all you’ll need to buy some dielectric grease so the cables are easier to remove next time.

http://www.jamestowndistributors.com...ct.do?pid=8196


1: Once you have removed the single cable, ( do only one at a time so you don’t loose the firing order. ) , place the ends of a ohm meter at the same time at opposite ends. Then measure the reading, it should read closely around 5,000 ohms if the value is higher than that the wires are in question. Plug wires will hold an ohm reading of around 5000 ohms for a long time, but once they begin to break down the resistance goes up quickly in carbon fiber cables.


2: A brief under hood inspection is a good way to check vacuum hoses are on and that none of them have been burned open by leaning against the exhaust manifold. You've touched every sensor connection to see if it's on tight, you've even checked for trouble codes. However, not everything calls for high-tech diagnostics and the latest scan tester. Engine misfire often is caused by leaking spark plug wires, so visual inspection could reveal what's wrong. The jackets may be damaged from the outside by abrasion caused by engine vibration (particularly at the plug-end boots), a hot engine compartment, spilled fluids or battery acid, multiple disconnections and reconnections for other service, or even a family of nesting rodents.
Run the engine in near darkness, and then look and listen. If you see little electrical arcs, or hear a snap-crack, there is high-voltage electrical leakage. Of course, running the engine at idle doesn't exercise the ignition system very hard, so you can add something to the test by spraying the plug wire ends with clean water from a household spray bottle.
Another test: With a jumper wire, ground the metal shank of a screwdriver that has a well-insulated handle. Then, run the tip of the screwdriver along the length of each wire and all around at the coil and plug boots. This will often produce an arc from the wire to the screwdriver.
Now look at the wires under good lighting. If they are damaged by abrasion, oil-soaked, cut, burned from contact with the exhaust, or have a dried-out look with heat cracks, it definitely shouldn't be a surprise if you see arcs in the dark under some conditions. However, if they look bad but there are no arcs, do a resistance check.
A conventional new plug wire has a resistance of 5,000 ohms , the wire probably is bad if the value is much higher than this. An absolutely failed wire will have a hairline break somewhere, and the resistance will be infinity.



3: Grab a water bottle sprayer and add a little regular dish soap and water and spray the spark plug wires WHILE THE ENGINE IS RUNNING in park. If the soapy water mixture finds a hole or soft spot in the spark plug wire the spark will jump out of the wire and ground itself to the water.
The engine will really miss and run bad once the spark comes out of the water. If you see the spark come out of the wire or the engine begins to run rough and miss when you spray water on the spark plug wires….you need new spark plug wires!
Watch the video……….


YouTube - How To Check For Bad Spark Plug Wires



I hope this helps…………. Chongo

 

[Donjames911]

Chongo,

First, thank you for taking the time to respond.

Second, I have a degree in Chemical Engineering, with a backround in electronics and physics (yes there IS a physical basis for a vacuum as opposed to pressure differential <grin>), thanks to military service aboard nuke subs. Also have rebuilt 2 VW Beetles and a Porsche 911 from the ground up, and in my racing days built an off-road 2 seat buggy starting with a basic frame. What I lack is experience with the Disco.

So feel free to get technical! I have already researched some of the things you mentioned, and the others have given me food for thought and approach. Thanks again for your advice! I will keep you and the forum advised of my progress.

Don James

 

[Chongo]

Chongo,

First, thank you for taking the time to respond.

Second, I have a degree in Chemical Engineering, with a backround in electronics and physics (yes there IS a physical basis for a vacuum as opposed to pressure differential <grin>), thanks to military service aboard nuke subs. Also have rebuilt 2 VW Beetles and a Porsche 911 from the ground up, and in my racing days built an off-road 2 seat buggy starting with a basic frame. What I lack is experience with the Disco.

So feel free to get technical! I have already researched some of the things you mentioned, and the others have given me food for thought and approach. Thanks again for your advice! I will keep you and the forum advised of my progress.

Don James

Chemical engineering…….. I chose structural engineering and physics, but anyways, awesome, and congrats on your degree. (yes there IS a physical basis for a vacuum as opposed to pressure differential <grin>), lol, that’s funny, I was once told in physics class, ( there is no such thing as Vacuum, the whole world sucks……) lol. And yes, it has a valid measurement application in our atmospheric environment, depending on altitude and density as long as it is measured against a known constant, i.e. 14.7 lbs/ sq. in. and the gauges are calibrated to that. Unfortunately it’s only as accurate as the known constant, if the constant becomes a variable, then the readings have to be measured against a known constant i.e. 0 lbs pressure. This is one of the reasons for the automotive and emissions engineers have drifted from the use of a map sensor, ( manifold absolute pressure), to a maf sensor. But for all automotive needs, any Vacuum gauge will do for diagnostics. The accuracy required to measure automotive diagnostic needs aren’t as stringent as scientific needs.

I don’t know about you, but I really liked my science classes, I thought my engineering classes were a joke compared to the science classes. They really answered a lot of my questions and basically gave me a different perspective on procedures, and point of view. The only subject not covered well when I went to school was plastics, of course they where somewhat in their infancy in 1983, and that might have something to do with it, and the college’s professor’s lack of experience, or familiarity in the field, and basically the college’s just weren’t up to speed on the subject in my area. I will say I disliked English with a passion. …….
Military service, me too, navy, desert storm and the oil field
Aftermath, all I’ve got to say is people in this country need to have more respect for their military people. I like Israel’s mandatory 2 years service program, we should do that, especially if you’re young and have nothing planned after high school…..

That’s too funny, my first car was a VW bug too, in matter of fact, the first 2 were VW’s, took me 4 hours to free the brakes so I could push the first one home and rebuild it……… I was 14.

One thing I remember in college, was one of my professors was involved with a science project in Japan. The test was to confirm the life of an atom. They had several pools, ( roughly Olympic swimming pool size ), filled with an electrolyte and many sensors to detect the energy of an atom when it’s orbital shells collapsed, of course highly subject to the Heisenberg principal I’m sure. But since energy is neither created or destroyed, it was based on this principal, and I graduated long before the results. Do you recall hearing about this? And did you hear of the results?

Anyways, when I respond to your questions I’ll cut out the layman terminology, lol.

I’ll send you my e-mail address on a private message, (pm ), to you.

Well, best wishes to you from one ex Navy guy to another…….
May your sails always be full and your waves be small……… Chongo

 

[Donjames911]

Joey,

You were spot-on. Cleaned the MAF (man, it was dirty), lubed the linkage, and Idle is back to normal. Thanks, bud.