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View Full Version : OT- Car Troubles/ OBD Readers



garagemark
01-21-2011, 06:12 PM
I have a 1997 Plymouth Breeze for a work car, and for the last six months or so it has been idling too slow, to the point of ALMOST dying. First thing I did was change plugs. I also changed the idle air control valve motor... to no avail.

I also have a pretty good OBD II code reader, but there are no codes set in the ECM. My reader will give real time readings of various sensors that can be observed during a drive cycle(engine running) . Only problem is that I don't know what the values should be at any given time. The maintenance manual does not offer this information.

Does anyone know where I can learn about what the sensors should be sending to the ECM in real time? I have searched the net for all I can think of. This has Nothing to do with the code reader function.

Bottom line is there is something wrong with my car's idle that does not set an ECM code. I don't want to just arbitrarily change various sensors or catalytic converters. So if anyone knows where I might look for guidance, I would appreciate the help.

Mark

RB211
01-21-2011, 06:18 PM
Can you simply adjust the idle position of the throttle body?
And for kicks, just unplug one of the 02 sensors and see if it throws any codes.

Liger Zero
01-21-2011, 06:21 PM
Also look for a vac leak. Almost dropped $2500 on a transmission, World's Most Honest Mechanic (Chuck Wolster) spotted the broken vac-line as he was preparing to drop the whole unit. Charged me for two hours labor and a connector-thingy.

garagemark
01-21-2011, 06:25 PM
Unplugging an O2 sensor is doable; adjusting the throttle body is not. Between the idle air control valve, manifold absolute pressure sensor, and throttle position sensor (damn electronics anyway), any movement of the butterfly would shoot false data to the ECM. The butterfly at idle must be totally closed.

When I changed the IAC, the ECM did set a code for it, but after a drive cycle I cleared that code and it did not reappear.

Mark

RB211
01-21-2011, 06:29 PM
Not familiar with your car, however I would look at the basics still. How does the distributor cap and rotor look? If the contacts and wipers are warn down to nothing, that could account for poor idling.

gnm109
01-21-2011, 07:35 PM
The low idle problem with generally poor performance happened to my 1998 Dodge Dakota pickup a few years ago. I got an OBD II reader and it had thrown a code for bad speed sensor. On the Dodge Dakota, the speed sensor screws into the tailshaft of the transmisison so it was an easy, inexpensive repair since I bought the part at the local dealer and installed it myself. It fixed the problem immediately and the Code reader cancelled the code, which did not recur.

In your case, without a code I wouldn't know what to do either.....

Pherdie
01-21-2011, 07:47 PM
Also look for a vac leak.
Ditto. I had the same problem from a vac. leak.....

Gravy
01-21-2011, 07:54 PM
The default first answer for low idle is pretty easy. Get a toothbrush and a can of throttle body cleaner (NOT carb cleaner - it can ruin seals) and clean the throttle plate and body. Just get the gunk out from where the throttle plate sits at idle. If that doesn't fix it, there are several dozen choices of Step 2.

vpt
01-21-2011, 08:00 PM
If it is the same as a honda there is a screen in the IACV passages that gets gummed up with carbon and makes engines idle low. Throttle body cleaner normally can clean it up.

Willy
01-21-2011, 08:05 PM
This sort of thing is hard to diagnose long distance as there are a lot of items that can cause a low idle problem and yet not trigger a code.
A dirty throttle body, a vacuum leak, a faulty power steering pressure switch, and a sluggish IAC motor are just some of the items that will affect idle quality and not trigger a code.

But your inquiry for insight as to the how to interpret the OBDII scanner's readings can be answered with a number of books. Have a look at some of these. You can browse through them a bit to see if they meet your requirements.
Also it is hard to beat a factory shop manual, always a lot more comprehensive than a generic maintenance manual.

http://www.amazon.com/OBD-II-Diagnostic-Secrets-Revealed/dp/0971541140/ref=pd_sim_b_2#_

Larry Backer
01-21-2011, 08:07 PM
99 Ford ZX2 Vac leak, PCV Valve in front of engine that connects to pipe that snakes around to back of engine and then goes into bottom of intake manifold, the rubber boot that goes into the manifold was worn out. The idol had the same symptoms as you are having with your car.

Larry,

garagemark
01-22-2011, 07:36 AM
Ah, Willy. The book of which you link is on order as of ten minutes ago.

I appreciate all of your answers, and yes, this is almost impossible to diagnose from afar. That's why I asked for the reference.... I must learn these things, as this will not be he last time one of my cars gets sick. Yon Know, I spent so much time searching Internet sources that I forgot to look at good old fashioned books. Anyway...

Until the book comes, I will re-check for vacuum leaks with carburettor cleaner. If I knew what the MAP was in the intake at idle, it would verify either a vac leak or a bad valve (not really expected; the car runs fine at speed).

I actually clean the throttle body quite frequently. It does get gummed up rather quickly; always has.

Thanks for the replies guys.

Oh, and did I mention that I HATE CARS. I'm just too cheap to have someone else fix em. :rolleyes:

Mark

garagemark
01-22-2011, 09:58 AM
Good Lord boys, I hate to even admit this: The intake manifold gasket is blown on not one, but TWO cylinders! A little carb cleaner verified this post haste. That's why the ECM set no codes- the leak(s) is behind the MAP sensor.

I feel like an idiot.

Mark

Liger Zero
01-22-2011, 10:00 AM
I feel like an idiot.

Mark

Why? Not an easy thing to diagnose!

gnm109
01-22-2011, 10:01 AM
At least you found the problem. That's when I feel the best - when I've found out what's wrong with the vehicle.


.

vpt
01-22-2011, 10:08 AM
Good Lord boys, I hate to even admit this: The intake manifold gasket is blown on not one, but TWO cylinders! A little carb cleaner verified this post haste. That's why the ECM set no codes- the leak(s) is behind the MAP sensor.

I feel like an idiot.

Mark


Time to trade it in on a nice reliable honda.

Metalmelter
01-22-2011, 10:08 AM
Good Lord boys, I hate to even admit this: The intake manifold gasket is blown on not one, but TWO cylinders! A little carb cleaner verified this post haste. That's why the ECM set no codes- the leak(s) is behind the MAP sensor.

I feel like an idiot.

Mark


Don't feel like an idiot - at least you posted what you found so others can read it and most importantly - LEARN ;)

I was just gonna post to do a real good search for vac leaks and swap out the IAC and clean behind the throttle plate but noticed you found a few problems. And they are hard ones to find too. I had my fill with almost 25 yrs of mechanics. Nice to see your on the right track ;)

Willy
01-22-2011, 02:00 PM
Good Lord boys, I hate to even admit this: The intake manifold gasket is blown on not one, but TWO cylinders! A little carb cleaner verified this post haste. That's why the ECM set no codes- the leak(s) is behind the MAP sensor.

I feel like an idiot.

Mark

Yeah don't feel bad you did find the problem, we all learned something!

I'm sure the book you ordered will come in handy in the future.
At least you'll be able to read it at your leisure.:D
Thanks for letting us in on your findings.

Liger Zero
01-22-2011, 03:15 PM
Do NOT return that book. Now that you have it you'll be able to keep this car in "awesome" condition for a long long time.

garagemark
01-23-2011, 10:08 AM
Thanks for the words of wisdom. I have been maintaining my cars for thirty five plus years. I should have know better, but these newer cars with their fancy electronics sometimes stump me. I'm looking more for codes and data than doing the basics. I have learned form this experience.

The most fun I have anymore is with my MGB. It has real points and real distributor and real dwell and real adjustable carburettors. You know, my day kind of stuff. But anyway...

Changed the manifold gaskets (really four molded O-rings) and fuel injector O-rings (hell I had it off anyway). The old girl runs like a new one again!

As I have many more vehicles (I'm insurance poor), I will not return the book. I think this OBD reader will pay for itself in a short amount of time.

Thanks again to all who kept me motivated.
Mark

I think I'll go do some woodworking today.

DICKEYBIRD
01-23-2011, 10:43 AM
...but these newer cars with their fancy electronics sometimes stump me. I'm looking more for codes and data than doing the basics.Very wise words there g/mark!

I still earn the daily bread working in a car dealership, although not on the shop floor for a long time now. I can't tell you the number of times through the years I've been out in the shop on an unrelated mission and walk up to a vehicle that's giving someone fits trying to diagnose. Usually it'll have enough electronic diagnostics equipment hooked up to it that it looks like a NASA launch and a couple or three talented techs standing around scratching their heads. I'll walk up, look around a bit and wiggle the loose battery cable, shake the loose ground wire, point out the split vacuum hose, loose harness connector plug, etc, etc.

We have good techs but sometimes they get hung up on the esoteric stuff and forget the basics. They're good kids though and accept my ribbing good-naturedly and absolutely learn from the experience. It usually happens only to a new tech once or twice though; they don't like to be embarrassed by some old guy that works in the office!:eek: