Unplug the the O2 sensor and car runs smoothly?

[84GNTTYPE]

When the 02 is plugged in, my car idles a little rough, runs rich, and has a slight "miss" to it.

I unplugged the sensor tonight and after a couple minutes it idled smoothly, not rich, and no miss. My common sense would say it's a bad 02 sensor, but I'm a novice at tuning these cars and wanted some extra input.

It doesn't throw any codes when the sensor is plugged in. I can post some scantool numbers if necessary. Tell me what you need.

Thanks.

 

[Jerryl]

Was the car cold when running rough?
Did you disconnect the O2 when she was warm?
Did she started running ok when warm or does that matter?

 

[84GNTTYPE]

The car has idled rough when its either hot or cold for awhile. Last night it was hot. I unplugged the sensor when it was hot.

 

[Jerryl]

What are your numbers?

O2
O2 CC
BLM
INT
TPS
IAC

 

[84GNTTYPE]

Numbers

Numbers with O2 Sensor Plugged in:

O2: fluctuates widely between 106-663
O2 CC: steadily climbing
BLM: 113
INT: 113-122
TPS: 0.48
IAC: 39


With O2 Sensor unplugged:

O2: little fluctuation from 446
02 CC: 0
BLM: 128
BLM: 128
TPS: 0.48
IAC: 18


All of the readings were taken when the car was up to operating temp.

Thanks
John

 

[Jerryl]

How many miles on the O2?
What is the TPS with the car off?
What are your MAF readings?

 

[84GNTTYPE]

The O2 sensor isn't more than two years old with no more than 3000 miles on it.

The TPS is the same with the car off: 0.48

The MAF readings are 7-8 with the sensor unplugged and 8-9 with the sensor plugged in.

 

[Jerryl]

Try to reset your TPS to 0.46 max with the engine off.
Your MAF looks high also and could indicate problem. MAF reading should be 4-5 at idle. Drive the car and have the computer learn the new setting.

Are you sure you have the correct chip for the set-up (injectors, FP etc)?

 

[84GNTTYPE]

I will reset the TPS tomorrow and try that.

The car is stock and, as far as I know, has a stock chip. What is the ID number for the stock PROM?

Thanks.

 

[Jerryl]

I am unsure of the stock PROM ID number. Do a search on this board and it should pull it up.

You stated that your O2 CC climbs steadily. Is it "lazy" and on its way out? Try changing the O2 sensor also if all else fails. It may not be old but if someone ran race gas in the car, it may have ruined it. If nothing else, for $25 you will have a spare.

 

[84GNTTYPE]

There has been no race gas ran in the car, at least since I had it. The previous owner was a little old lady . . . so I doubt she was running any either. In any case, I replaced the sensor after I had the headers welded.

What is a good brand of O2 sensor to use? The last one I put in was a Bosch, but is there a better brand I should be using?

Thanks.

 

[Jerryl]

There are differences of opinions on this. Most on here will recommend the GM O2 sensor - AC Delco

Make sure to verify/adjust the IAC after you adjust the TPS.

 

[84GNTTYPE]

I adjusted the TPS and IAC and the engine no longer runs rich, so that is good.

Replaced the O2 sensor with another Bosch sensor. Called the GM dealer and they wanted $55 for one. Talked to two different parts stores and they told me that Bosch makes all of the O2 sensors anyway. Not sure if this is true, but it sounded good.

The car still stumbles at idle with the O2 sensor plugged in and idles smoothly with it unplugged. Could this problem be do to electrical gremlins? I've known that I had electrical problems for awhile, but only the lighting system seemed to be affected. I was going to start testing things with my multimeter tonight, but the battery was dead in it. Will get a new one tomorrow.

If there is a chance the electrical prob is affecting engine performance, I'll start tracking that down right away.

Thanks for all your time.

John

 

[Jerryl]

You are making good progress.

Now, verify the battery is FULLY charged and that the ECM is seeing 13+ volts. Verify your charging system and check ALL grounds. Also, verify the coil pack is good.

What is your MAF reading at idle?
Forgot if you checked your plugs and wires (??)
One step at a time .................

 

[84GNTTYPE]

I finally got some to get to working on the car again.

How do I verify that the coil pack is good?

What are the major grounds I should be looking for? Just want to make sure I don't miss any.

I'm going out this evening to start testing. Already tested the alternator and battery and they are fine.

Plugs and wires are pretty new (2 years), but what should the resistance of plug wires be?

MAF reading is 7-8 at idle, sometimes dipping to 6 or hitting 9. I've heard that tapping on the MAF and listening for engine stumble is an easy way to test the MAF. I did that and observed no problems.

Thanks.

 

[buickpower]

i have similar problems

I have problems similar to yours, most of my numbers are similar to yours on the scanmaster, low blm's, maf reading 8, my tps was high (.48), and I reset it, after lowering IAC numbers (which were close to yours also) with the minimum air adjustment screw. I also have a bosch sensor, and it went lazy so I replaced it, although it didn't seem to help all that much. What maf sensor do you have? Mine is a remanufactured unit, one of the crappy bottleneck ones, but it is all i can afford right now. I am wondering if this maf sensor of mine is miscalibrated or something of that nature, but I will have to wait to find out. It stalls if I unplug it, and won't seem to start without it.

To do a static measurement of the coil pack, you can check the resistance across each of the three towers, and they should measure ~11-13kohms, although this is not always accurate since the coil pack is not under load. The best way is to find someone with a coil pack tester who can verify good spark under load (I have yet to do this as well). As far as the grounds, the major ones I can think of are the big ground w/ several smaller wires that are grounded to the lower alternator bracket, the ground from the firewall to the driver's side valve cover, the small negative wire that goes from the negative battery terminal to the body close by.

Good luck and keep us posted,
Mike

 

[84GNTTYPE]

I checked the grounds --- they're all fine. Haven't checked the coilpack yet.

I think I may have found a vacuum leak at the vacuum block. I'm not sure yet if it is leaking through the throttlebody to vacuum block gasket, or out of the unused vacuum port.

I checked my MAF --- its an AC Delco unit. Is there any way to verify it is working properly?

Thanks.

 

[buickpower]

Not that I personally know of off hand, all I have heard of is the swap method. By the way, do you have an AC Delco PCV valve? that is the best kind to have for an accurate idle, and it doesn't hurt to replace it since the springs can gradually relax. However it does sound more like a vacuum leak like you mentioned.

Mike

 

[84GNTTYPE]

I replaced the PCV valve last year with a Purolator one. Pretty sure I fixed the vacuum leak and it still does the same thing. I'm getting an intermittent Code 22. I'm going to start a new thread for that one.

Thanks.

 

[Jerryl]

.... Pretty sure I fixed the vacuum leak and it still does the same thing. I'm getting an intermittent Code 22. ..........

Did you get the code 22 all this time?