I need your opinions my car runs really bad when it's cold. I can't even drive it until it runs for about 5 minutes then I can drive it with no problems. But if I try to drive it before it warms up it studders real bad and it throws a code for the o2 sensor I can't remember the code tho I haven't been driving the car and the code has been erased. It's deff the front o2s since the rears have been deleted. I'm thinking the heater in one of the o2s isn't working properly and causing the car to run bad cold then when the sensor gets warm it runs great. What do you all think?

 

Just a long shot..but possibly the temp sensor..the one in the waterpump. Perhaps it is bad and the pcm is thinking the car is already warmed up and it is not utilizing the cold start parameters.

 

I would think if the temp sensor was bad it would throw a code. The only code I'm vetting is for the o2 sensor. I guess I should drive it and see if i can make the code comeback so I can scan it again.
Thanks

 

Coolant temp sensor only sets a code if its an open cricuit or a short circuit. Does not set a code for the temperature being lower or higher than actual.

You need to get the code. If you haven't pulled the power to the PCM, the code is still stored in the PCM. If you did pull the power, drive the car long enough for the SES light to come on, and scan it.

When the O2 sensor is "cold", it doesn't put out a signal, so the PCM ignores it. The code in OBD-II would set based on the amount of time it took for the O2 sensor to reach operating temperature.

Have you ever done a data log? May be you have screwed up long term fuel corrections (BLM's) and the PCM has to use both the long term and short term corrections to make it run right, but it can't use the short term corrections when the O2 sensors aren't accurate. It locks them at 0% (128).

 

No I never datalog.well when the car is warm it's tough to start up I have to start the car at wot. And when cruising normally I can hear the motor stumbling real faintly.And when I come to a stop the idle dosent drop down right away. I'm thinking all this stuff is connected somehow. I have a mail order tune done I think the tune might be a little screwed up. I'm gonna to try to get the code. I have a cheap code scanner.

 

I got the code today P0135

 

I'm gonna have to strongly recommend against starting a car at WOT for any more times than it takes to diagnose your problem. Any leap in RPM above 3.5k or so when cold starting puts massive stress on valvesprings and will tear your bearings up in the long-run. those kind of starts are why both my engines, the LS1 and LT1 died at ~90k miles

but fixing it depends on that code. with no code we could shout wrong things all day

edit: I'll add that I bought the LT1 broken, and the LS1 I had bought with 75k so it WASNT ME =)

 

P0135 is the code for oxygen sensor on the driver's side, pre-cat. You can try swapping the sensors from side to side and see if the code changes to the passenger side. Could also be the harness or connectors.

 

Tomorrow I'm going to check my wiring and check the voltage and I'm going to switch the sensor and see what I come up with.
And when I start it at wot it never passes 1200 rpm I would never rev a motor that high starting it up I deff no better.

 

haha just making sure! Hey when I was 16, i was like "wow my car has more power when i first start it! lets go fast!! I'm amazed that 3.4L lasted past 160k.

 

If you replace both these and clan the MAF you will fix the problem.

 

P0135 sets when the sensor does not heat up as fast as the PCM calculates it should. Could be a problem with poor voltage on the sensor heater circuit. Do you have a harness extension on the driver's side?

Putting your foot on the floor while cranking puts the PCM in "clear flood" mode. The PCM significantly reduces the fuel flow. That would indicate its either flooded before you turn the key (leaking injectors), or the PCM is setting a too rich cold start A/F ratio. I've seen that caused by a faulty coolant temp sensor.

 

I have a extension on the driver side which I made myself. Do I just use a volt meter and find the black wire and see if it's putting out 12v?
And as for the wot start I only have to do that when the car is warm. I really think the tune is off. It's a mail order tune from pcmcforless.

 

The black wire is the ground. The 12V power is supplied by the brown harness wire. See wiring diagram from Shoebox:

http://shbox.com/1/1995_pcm2.jpg

Again, putting the pedal on the floor means it needs the "clear flood" mode. This sounds an awful lot like my son's Saturn with a faulty coolant temp sensor. $18 for a sensor solved problems that had a dealer recommending a new engine . I doubt the tune would be causing it.

 

Ok brown wire I'm going out right now to mess with it. I will order a coolant temp sensor tomorrow and see what happens they are cheap enough.