A scanner would say if he's in open or closed loop. However, O2s do go bad or maybe the connector has been tweaked/burnt on the header. A quick visual wouldn't hurt.

It seems like the surge could be coming from false air. Have you sprayed around to see if your RPMs change?

I have seen a similar concern with a clogged cat. It was clogged and the pressure would build up which would cause the rpms to drop. This would build pressure on the pre-cat side of the collector. When the pressure built up high enough, it would blow through the partially clogged cat which increased the idle. The cycle would repeat.

These are all theories without being there, but check the O2s and their connectors, spray for false air, and perhaps your cat is getting clogged.

 

BTC and Wild1, the headers are coated, but I bought them used so the inner coating would have been burned away by then. I would imagine the O2 sensors are fine. I replaced them just over a year ago as well, so they are pretty new. I have sprayed around for false air and didn't get any change in RPM. Also, I have an off-road Y pipe so there are no cats on the car.

I recently had the car scanned and the only code was P0300 for random multiple misfire. I didn't get any O2 sensor codes. Would I get a code for the O2 sensor if the wires or connectors were burnt?

 

I had a problem that fits your symptoms perfectly. First, the LCD that I have on my scanner that goes on and off is the one that indicates the engine is in closed loop.

Second, remember that the engine starts in open loop then after reaching a predetermined temperature, it switches to closed loop.

After nearly 2 years, the wire going to the right O2 was burned and caused my engine to run crappy. It would start ok and run fine until it got warm. It would idle bad, then rise up in RPMs, run good for a few seconds and start all over again.

When I scanned it, I found the right O2 stayed rich (the signal stayed higher than 450mv). After it finally went to closed loop, the pcm would see the right side was rich so it kept pulling fuel until it got as lean as it could and the PCM would jump back to open loop (LCD on scanner off). The fuel trims would go back to neutral and then it would go to closed loop and start the whole process all over again. Up and down. Up and down.

My short term solution was to unplug either O2 to force it into open loop while I drove it back and forth to my work area.

The next thing I did was to put a jumper in the O2 connector to put ground on the 2 signal lines. This should make the O2 readings stay very low. But mine did not change from being high all the time. I knew at that point the wiring was a problem.

The wires burned under the foil wrap near the header going down from the top of the passenger inner fender. The wires were all burned and discolored.

My advise to you is to scan it for real time O2 data and fuel trims. HOWEVER if you don't have access to a scanner try disconnecting an O2 sensor. Doesn't matter which one and see if the problem is gone even after it warms up.

Then there are some things you can do to help isolate the problem even without a scanner. Like the ground jumper I mentioned.

The only problem with this theory (if you will) is mine is OBDI which does not have a DTC for insufficient activity of the O2. Yours is OBDII and if you had this problem, I would expect to see a an SES set and either a DTC0154 or a 0134 for insufficient O2 activity.

So I may have just wasted countless time typing all this for nothing.

 

Speedy, I appreciate the response. With my car being OBDII, does that mean I can unplug the O2 sensor and perhaps that will isolate the problem?

 

is your SES light on? go to autozone and have them scan your car for free, then see what codes pop up and go from there.

 

Ok, I went under the car and found the O2 harness extension that I made laying up against one of the header primaries. I pulled it out, cut out the charred section and soldered it all back together. Put the car back together and it seems to run fine. It still idles like I've described in other posts though. No SES light on. Now I'll update this thread in a few days because with all the other things I've replaced, the car ran fine for a day or two and then went to crap so I'm not getting my hopes up just yet.

With the idle still being weird, do you guys think I need to just replace the IAC valve?

 

without scanning it, I would say no. Look at it and clean it. And to answer your question. Yes if you unplug one of the O2s it will set an SES but it will also stay in open loop. If it runs better then you know it's a closed loop problem.

 

A while back I had an idle problem. I put Autotap on and discovered that the voltage for the TPS was flopping from .2 to .5 Volts. If the car started up with the low setting, when the higher voltage became present, the idle would climb up. I had replaced the TPS and IAC to no avail. Cleaning was another waste.

The solution was a swapout of the PCM. (lucky me I had two), reflashed the PCM with my Lt1-edit prgrm and 'Voila'...problem gone.

the voltage for the TPS comes from the PCM. I may have had a bad connection, or the power supply for the TPS may have been flaky.

 

Ok, so after repairing the burnt O2 harness, the car is still running badly. i.e. runs fine for a minute then starts to shake/shudder/stumble (misfiring). It's not quite as bad as before but it's still present. My IAC valve was dirty so I cleaned it but did not replace it. Do you guys think that replacing it will clear up my problems?

 

Unfortunately, I still recommend scanning the computer for current data and watching the O2 activity. It may not be throwing codes but cutting and splicing a harness could be an issue. Some O2s sample air through the insulation. After crimping or soldering, the insulation has been somewhat affected which could alter the proper operation of the O2s.

 

I didn't cut the O2 sensor's end of the harness. I cut the computer's end. Everything that is attached to the O2 sensor is untouched so the insulation that it would sample through is unchanged.

 

Well I replaced the IAC valve today, reset the IAC position as per shoebox's website's instructions, and nothing has changed. Fortunately I was able to get my money back for the part but I'm still in the same situation I was in before.

 

Finally decided to get back under the car today after many weeks of frustration and just putting it off. I theorized that the burnt O2 sensor harness might have shorted the sensor out. (more than one wire burnt, probably touched more than one at a time on the header) Well I unplugged both O2 sensors today and the car ran fine, other than smelling like it was running richer than all hell. So I'm thinking I can replace one (or both) O2 sensors and the car will be fixed. Do you guys agree?

 

i do

 

Is there any way to get a scanner on there (Autozone or a local garage) to view Current Data? Your O2s should be switching from .100 to .900. Find if one or both are lazy then replace the confirmed dead sensors. They can be pricey. Do not get the splice type, be sure to get one with a connector that matches the car. If you splice in a crimp, you may run into corrosion troubles in the future along with the possibility of hampering the sampled air through the wire.