Strange Idling condition

[Whiskey River]

Here goes, when I start the car, hot or cold, it purrs like a kitten, smooth as glass. When I put the car in gear, the revs drop to about 600 rpms, still smooth, if I put the car in neutral or park, the revs go up to about 700-750 and it shakes the whole car. I blip the throttle and it runs up to 900 rpm and once again, smooth as glass. I have cleaned the IAC and replaced the TPS. I cleaned the TB while I had it apart. I have recently checked the plugs and replaced the plug wires (another story). I checked the vacuum hoses and the only hose found that was worn was the vacuum dump for the cruise control. My next step is to wire up an ALDL adapter and hook a laptop to it to test the MAP sensor. Anything that I might have missed? Any ideas? Thanks.

[Whiskey River]

Well, I figured out what it was, I assembled an ALDL connector and upon monitoring it with my laptop, I found out the O2 sensor was/had gone bad but not bad enough to trip the ECM. It was throwing out very erratic readings. If anyone wants schematic's for an ALDL adapter, just PM me and I'll forward all that I have. It's a very easy circuit to make and it will work with any ODB-I GM cars. As for the monitor, I used FreeScan 2.07 by Andy Whittaker. Worked really well for me.

[96montyZ34]

hi, what type of cable do you use to connect your computer to the car ?

[Whiskey River]

It's a very simple circuit. If I had pics of it I would post them. Currently it resides on a breadboard. Once I find a suitable perforated circuit board, I'm going to solder it together. All it does is convert the +5V Pulse Width Modulation signal into a +/- 12V signal the computer can understand. After I assembled all needed parts, about $22 dollars worth, it took 45 minutes to put it together. I had thought about producing 5 or 10 more but I'm not a bank and I would almost need guaranteed orders before I want to sink that kind of money into it.

[lukee1982]

hi, what type of cable do you use to connect your computer to the car ?

 

i was wondering that too. is it possible to do the same thing with obdII :?: :?:

[Whiskey River]

i was wondering that too. is it possible to do the same thing with obdII :?: :?:

 

It is possible but the circuit is quite a bit more complicated. Requiring power from the car instead of the laptop (how mine is currently powered now). From the looks of the schematics I would guess the cost to be around $40-$50 for parts, still cheaper than the $150 plus for prefab converters that I have seen on the market.

[gimp19]

I wonder if the 02 sensor could be causing my cars idling problem. Ever since I got it 2 years ago when the weather is hot 70+ degrees it stalls just about every time I start it. It has never stalled in colder temps 60- degrees. At first I thought it was the MAF sensor untill the MAF triggered my "service engine soon" light and I replaced it last summer (it was causing my car to shutter at constant speeds w/cruise on). I know somthing is wrong cause my gas milage likes to fluctuate from 19+mpg to 15-mpg cty/hwy combined. Anyone have an idea? What ever it is my "service engine soon" light is not being triggered.

[Whiskey River]

Well, the O2 sensor doesn't come into play until it heats up. Usually between 1.5 and 2 minutes, on a cold engine, sooner for a warm engine. Does it stall immediatly after starting it or does it stall when you first put it in gear??? Also, let us know what you have already changed, aside from the MAF.

[gimp19]

Usually it stalls the first time or two right after i turn the key unless I give it alittle gas before it has a chance. So basically my remote starter is useless in the summer time becauese 9 times out of ten it stalls unless I hit the gas quickly. I'm not really worried about that because I dont use it much anyways it came with the car.

 

It runs better when I put it in any gear besides park. I usually back out of my parking lot and it kind off thumps alittle when I put it in reverse because of the engine surging but after the initial shift it idles fine. It dosnt stall after I drive it even if its just a few feet untill its sits for awhile and I have to start it again.

 

I have changed two sensors related to the cooling system witch couldn't be the cause of this problem anyways. I had the throttle body/fuel system cleaned last year, the air filter is new, most of the exaust is only 2years old (i'm not sure about the cat), the alternator is new but i'm not sure about the battery. I think thats about it.

[lukee1982]

It is possible but the circuit is quite a bit more complicated. Requiring power from the car instead of the laptop (how mine is currently powered now). From the looks of the schematics I would guess the cost to be around $40-$50 for parts, still cheaper than the $150 plus for prefab converters that I have seen on the market.

so you have the schematics for obdII ?? if so please send them

also i might as well have the obdI also

that would be great

lukee1982@yahoo.com

[slick]

Mine does the same thing. In park, its fine. But once I put it in gear, it drops to around 600 rpm then goes up a little and it idles really rough. Which O2 sensor would it be?

[Whiskey River]

Mine does the same thing. In park, its fine. But once I put it in gear, it drops to around 600 rpm then goes up a little and it idles really rough. Which O2 sensor would it be?

 

My car had only one O2 sensor, it was on the back of the motor on the downpipe. My last car liked to eat O2 sensors so I bought an O2 socket. I spent more time leaning the motor forward than I did changing the sensor. Also, I know there is a tool made that fits in place of the torque strut and allows a person to rock the motor forward with a wrench or air ratchet at least, where do you find one? I never thought to ask the mechanic when he was working on the car.

[Robby1870]

I think 3100s have two O2 sesors, one for each bank

 

Robby

[cutlassdude96]

OBDII gives you 2 O2 sensors 1 before the cat and one after the cat. anything older then 95 theres just one.

[Robby1870]

OBDII gives you 2 O2 sensors 1 before the cat and one after the cat. anything older then 95 theres just one.

 

I would hate that one after the cat. My car would definitely fail emissions. Good thing they make things that will trick that O2 after that cat to make it think the emissions are right

 

Robby

[cutlassdude96]

yep they do, some people use a high flo cat and not worry about it

[91cutty]

My car just started doing something strange today... very similar to the rough idle problem you described but not quite. When I start the car and leave it in park all is fine. Put it in drive and idle will yoyo between 500-1000. When when I'm driving all is fine again until I slow down. When engine slows down to 600 rpm the car either stalls, or almost stalls and continues to yoyo again. It did this a while ago but went away the next day, but now, 4 months later... it's back and it's not going away this time!

[slick]

Thats what is happening to me. But its not dropping to 600 anymore, its doing the rough idle at around 1000. And as 91cutty described, it almost stalls, except that i give it gas really hard so it doesn't die. I've also noticed that my gas mileage is a little worse too.

[91cutty]

did an idle relearn... problem solved!