OT- Car Troubles/ OBD Readers

[garagemark]

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]

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]

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]

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]

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]

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]

Also look for a vac leak.

Ditto. I had the same problem from a vac. leak.....

[Gravy]

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]

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]

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-Diagnos...ref=pd_sim_b_2#_