Hey guys. I need some help. My 96 vin K 190k bonne has a rough idle, and low mpg about 20 highway. But still no codes, has been happening for the last 1.5 years, progressively getting worse. The problem is there when cold, but gets worse once warm, may have to do with higher idle when cold. Based on an old post I found, AZU had the same problem 1 year old plug wires were bad. What do you guys think, is there anything else I should be looking for. Here is what i've done in June 2010. Then things about 2-3 years ago. This pretty much captures everything that was replaced or checked.

When I did change the plugs and wires in June. I noticed the back plugs were all brown and black, while the front plugs were grey/white.

June 2010
Checked coils (good)
Checked FPR (no fuel smell)
New alternator and battery
Cleaned MAF (but remembered i cracked something on the plastic casing)
New LIM gaskets, and upper intake, sprayed throttle body but did not clean any connecting components
New Radiator and flush
Cleaned ground busses on floorpan
New ac delco plugs and wires
Newer fuel lines
Newer brake lines
New Fuel Filter
Fuel system cleaner
New pcv
New Air filter

2 years ago
Transmission filter and fluid change
Changed all ignition coils
New water pump
New Belt
New idler pulley
New washer fluid pump

6 years ago
Head gaskets and head service
LIM gasket and UIM

Has the O2 sensor ever been changed? Also make sure none of the spark plug wires are touching the O2 sensor wires.

Have you checked for any vacuum leaks?

Thanks guys. I knew I forgot something. The 02'* were changed in June and the wire 02 wire is about 2 inches away from the nearest plug wire. A majority of the vacuum lines were replaced then checked for leaks with carb cleaner. No change in rpm.

The problem seems to be getting slowly worse as time goes on. In June, the engine would stumble every so often, now at idle its almost constant. The rpm drops maybe drops 50 then goes back up, then down up, so on. Now the majority of the time the rpm is down at idle. Acceleration is still spot on, no noticeably missing except for poor gas milage. I may just wait for a code to pop up, its bound to happen sooner or later.

I noticed the back plugs were all brown and black, while the front plugs were grey/white. This has gotta mean something, a sign of the failure, but I just won't know enough about engines. Maybe my back head gasket is leaking or the valve stems seals are going bad. Maybe it doesn't mean anything. I don't know

You will want to make sure the O2 wire is as far from the plug wires as possible. If possible, have the O2 readings scanned and logged. You want a nice even curve for the readings. Seems like the O2 sensor is going out. What brand did you change it with.

Thanks Danthurs. Im pretty sure I used AC delco from rockauto. I remember reading posts and intentionally not buying bosch. Nor would I have bought any other brands, except maybe denso. If my memory does serve my correctly, the ends were different, stock versus replacement, i believe the new ones had a series of holes rather than slits. I tried looking on rockauto but my order history only goes back to January 2010, is there identification on the sensors? I could pull one and let you know the type.

According to what I wrote in my manual they were replaced 12/4/09, not in June. Geez doing so much work on both the bonne and truck, I kinda got things mixed up, my O2s for the truck were replaced in June.

This could possibly explain the problem and why I've been experienced the problem the last year and or so. Seems legit.

So is it possible to scan the O2'* myself, or at autozone. Or will i need to take to the dealer.

You need a scanner that can scan live data.

Alright so not possible to measure voltage or resistance with an ohm meter while running. Like plot data reading every 1 minute or something.

I don't know anything about scan tools. Is there a cheap scan tool that you recommend or do you know anyone that lives near Louisville, Ky that will let me borrow one (LOL). I've just pumped so much money into the bon bon lately....

Needs to scan in real time. Here'* a scan, the O2 is the B1S1 line, second group from the bottom, lite blue line.

Thats pretty sweet Danthurs. I wish I had a supercharger.

Is there an economy scanner you recommend? Im not sure what to look for.