inconsistent air/fuel and idle

[sidallmighty]

hello ive read what i could find related to this problem but i couldnt find anything exact to what im experiencing.

ok so heres the deal, i start the car and my idle sits around 1300 rpm with an AFR of bout 13.7, ill let it sit and idle for about 10 minutes, afr drops to about 11.5-12.0 and my idle increases to about 1400.

ill drive at about 65-70 mph with an afr of around 12.0 which seems normal

i stop and go in a store for an hour or so. i come out fire it up and now my afr is at 10.7-11.5 and im idling at about 15-1600, ill drive home, ill slow down to stop at a stop light and my rpm fluctuate between 1100 and 1600 up and down until i come to a full stop, once im at a full stop my rpm's are sitting at about 1000.

now this will happen in any order, at any time it chooses, it seems to drive fine when im actually on the throttle, but once i let off it starts acting weird

ive worked with the biss, and the iac, and it will temporarily fix the issue until i take it for a quick drive to test the idle after stop and go conditions. i cant figure it out, and im paranoid about blowing my engine. please help

 

[JamesH]

Any vacuum leaks? They can exhibit these types of symptoms.

 

[JusMX141]

Vacuum leak, bad FPR, bad o2 sensor.

 

[sidallmighty]

is there a way to test the o2 sensor so i dont spend money on one if its good?

 

[Calan]

ill drive at about 65-70 mph with an afr of around 12.0 which seems normal

Normal would be an AFR of 14.7:1 during light load cruising and idle.

But this begs the question... how do you know what the AFR is? Please update your profile with any mods you have such as a wideband and logging software.

It sounds like a bad O2 sensor so far, but we need more info as to how your car is set up.

 

[manifestmessiah]

Best i could come up with, hope it helps.

start the car and let it run until the vehicle is warm, which usually takes about five minutes. The oxygen sensors must be about 600 degrees Fahrenheit to provide an accurate reading. This will cause the engine to become very hot, so be careful.

backprobe the oxygen sensor's signal wire. Be very careful when using the backprobe, because the plastic connectors are often very brittle and can break easily.

Connect the positive lead from the digital voltmeter to the backprobe.

Connect the negative lead from the digital voltmeter to a good solid ground point on the chassis of the vehicle.

Turn the voltmeter on and set it to the 1 volt scale. The voltage of the O2 Sensor will fluctuate between 100 and 1,000 millivolts, which is 0.1 and 1.0 volts, so having a quality volt meter is important.

Turn the vehicle back on and check the reading on the voltmeter. The reading should fluctuate rapidly. If the reading stays at around 0.5 volts, ensure that the vehicle is fully warmed up. If the vehicle is warm and the 02 Sensor reading does not change, then there is a problem with the 02 Sensor.

Or you could use Map gas to induce a vacume leak.

Oh also if the O2 sensor was bad it would throw a CEL. you could also graph it using a scanner

 

[sidallmighty]

Gotcha

 

[Colt4G63 also]

ill drive at about 65-70 mph with an afr of around 12.0 which seems normal if I were pulling a 25' camper up a steep hill.

Fixed