Slight Misfire at idle

[Avatar]

Hi, I have a 1993 toyota camry LE with a 2.2L Motor and I have been having a slight issue at idle for a while.

this is what I've done so far:

1. Compression check - Good
2. Checked Vacuum lines - Good
5. Checked Distributor / wires / plugs (Air gap, coil resistance, plug resistance, spark gap, inspected dist. cap) - Good
6. Checked MAP sensor - Good
7. Checked / Cleaned intake (EGR, IAC, VSV, TPS, throttle body)
8. Replaced ECU with known good ECU - problem still occurs
9. Checked Injector resistances - Good --- I also had the injectors cleaned while the head was off too so I know the injectors are not clogged
10. Fuel Pressure test - Good

I am stumped. Its nothing that really affects driveability, there is no CEL popping up. Its not really noticeable enough to call alarm to, but I can feel the motor every once in a while just miss lightly. I also did a Leak down check because I thought maybe one of the valves weren't seated correctly when i replaced the head gasket (Valves, seats, seals new), but it was and it checked out too.

I am thinking it has something to do with the Oxygen sensors, but I dont have any tools to monitor the upstream and downstream sensors.

I was searching online for an OBD1 to USB tool with datalogging software but haven't been able to find anything besides an actual hand-held data stream tool. Any suggestions on where I could get an OBD1 > USB tool with Software to hook into my laptop?

Thanks in advance

[fenixus]

how do you know there is a misfire? usually CEL starts flashing when it happens and ultimately you get a solid CEL with a code either specific to cylinder or random.

what spark plugs and wires do you have on it (and how old)?
how old is the fuel filter (and what brand)?
how is air filter doing?

also make sure the intake hose is free of any cracks (even micro cracks, hard to notice).

I believe OBD1 has no PC USB interface available for live monitoring on a PC. However there might be a serial port interface but that most likely would be Toyota specific device with some proprietary software for it. sorry I have not much idea about OBD1.

[Stillrunning]

Originally Posted by Avatar

have been having a slight issue at idle for a while.
I am thinking it has something to do with the Oxygen sensors

If mis at idle and not at speed then usually fuel trim(vac leak/rich), if mis at speed (especially under load) then usually electrical. If it is an oxygen sensor then it should show up in the color of the plugs, too white for lean, black for rich. You can pull the O2 sensor and test it. You can also Goggle for plug color reference. I'd suspect a vac leak but not one as obvious as a vacuum line unless it has a small crack. If the mis is not there at idle cold start-up and is there at hot idle then probably vac leak as rich cold start-up will hide minor vac leak. As Fenixus says check for intake hose cracks as well as possible leaks at intake manifold since you just did the HG, even o-ring leak at an injector will cause a vac leak. I'd use propane method to locate. You can also remove plug wires one at a time to see if it's cylinder specific by noticing no change when wire is disconnected.

Originally Posted by fenixus

usually CEL starts flashing when it happens and ultimately you get a solid CEL with a code either specific to cylinder or random.

Probably not on an OBDI.

[Avatar]

its not enough to change the idle really. It barely moves in rpm, I can just hear the motor hesitate slightly at idle. While driving (L-2-D-R) Its not noticeable. I know for a fact there is no vacuum leaks. I have a used EVAP Smoke machine that I purchased at an auction from a shop that closed down and I had no smoke coming anywhere besides out the throttle body a little because I didn't plug the TB Inlet. I am using Denso spark plugs, I did a tune up the same time I replaced the head gasket (Toyota Fuel filter, All OEM Ignition parts (high tension wires, rotor, dist. cap).

I will pull the plugs and re-check the gap, look at the condition of the plugs and also check the O2 Sensor.

Again, the miss isn't noticeable enough at idle to call alarm .. its just been doing it for a couple years and I figure since I am not super busy to check into it. If i cant figure it out its not a huge deal, but It would be nice

[Avatar]

Well I went out today and Connected TE1 and E1 together and raced the motor for 90 seconds at 2500 rpm. After that I connected VF1 and E1 to my multimeter and Counted how many times the Voltage fluctuated which it was more than 8. So I disconnected Te1 and E1 jumper and Raced the motor at 2500 RPM measuring the voltage output and it was 2.267 .. It was fluctuating around .003 Volts every half second. Repair manual indicates if it has more than 0V to "Replace the Oxygen Sensor".

So I am assuming that the Oxygen sensor is not doing a proper job and will need replaced. Can anyone confirm this?

Also, I did not pull the spark plugs yet

Edit:

After some researching, I have determined that the Oxygen sensor is culprit. When the computer receives a rich signal (high voltage) from the O2 sensor, it leans the fuel mixture to reduce the sensor's feedback voltage. When the O2 sensor reading goes lean (low voltage), the computer reverses again making the fuel mixture go rich. My Oxygen sensor is staying at high Voltage, so it is reverting to a Lean Condition (Limiting the fuel) Causing it to not have as much fuel as it should (Random Mis-fire).

Thanks for the feedback, I will replace the O2 sensor and re-test and post back

[fenixus]

nice troubleshooting

oxygen sensors (thimble type) usually do not last much longer than 100k miles. I replace them as a part of major tune up. get new Denso OE ones from ebay, they are much cheaper over there.

check for part numbers here:
http://www.densoaftermarket.com/catalog/

[a94autoCamry]

keep us posted if the new o2 sensors fixed your problem

[Avatar]

Update for you all

I installed the new oxygen sensor today and my idle problem is fixed! No more slight mis-fire at idle anymore, with the motor cold or hot! Hard to believe that a single Oxygen sensor could be that annoying!! Voltage readings are right along what the repair manual lists too. I will post back if anything changes

[fenixus]

[a94autoCamry]

question: when you drove the car...did you ever floor the gas pedal and did it bog/hesitate when you did so??

Glad to hear the o2 sensor has fixed the problem

[Avatar]

Originally Posted by a94autoCamry

question: when you drove the car...did you ever floor the gas pedal and did it bog/hesitate when you did so??

Glad to hear the o2 sensor has fixed the problem

no, I don't recall having a hesitation problem while I was accelerating