Rough idle due to O2 sensor?

[1stGENracer]

What would cause the rough idle on my car? I was thinking it is my O2 sensor? Would that cause my car to idle rough, and jump up to 1100rpm's then down to 650 rpm's? I have a new pocketlogger, and the O2 sensor seems to be reading fine, it goes from 0.04 volts to .96 volts when it is idling rough. I'm not sure , can you guys help?

 

[Enigma_Man]

If your O2 sensor seems to be working correctly, I wouldn't suspect that.

I know mine is dead, and I've ordered a new one, and I always have sorta rough idle, but it could be due to any number of things.

Some good things to check would be:

1) Do an intake leak test. Basically you build a thing that can cap off the turbo inlet, and has a tire pump attachment to it, so you pressurize the intake while the car isn't running so you can listen for leaks. This will cause a whole host of problems, from running rich/lean/poorly, to bad idle, poor performance, etc.

2) Make sure all the wires are attached well at the battery, and that the terminals are clean, and free of corrosion. I don't know how many "weird" problems I've had that have been solved by cleaning the battery connections. Anything from bad idle, to what felt like random fuel cut, to no-starts, to poor acceleration. So many things depend on good electrical connections in these cars.

Hope that helps out some, That is where I would start, people here are very knowledgeable, and might have something to say about the BISS and such, I don't know much about that yet.

*edit*
Another thing I thought of, If you have a datalogger, make sure that when you are idling that the car reports that it is trying to idle. If your throttle cable is maladjusted, the car sometimes won't know that it's supposed to idle, and will idle inconsistently.

-Jesse

 

[1stGENracer]

Ok, well I am going to make one of those leak testers on tuesday, so I will check for leaks. Thanx.


Also on my datalogger, the little Idle switch thing turns on when I push the throttle, and tunrs off when idling.

It looks like this when I'm on the throttle.

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and that TDC sensor thing is flashing on and off, doesn't stay steady on.

 

[Zerocygnal]

The only common thing I can think of that usually causes that problem is a leak from the intake tract or a vacumn hose disconnected. I would check the BISS screw personally. Other than that Not a clue if your fuel and ignition system is in working order.

 

[1stGENracer]

BISS screw is there, maybe it just needs to be adjusted a little.

 

[jizzo007]

i'm having problems that are very similar. what is the biss screw and where can i find it? and once i've found it what do i look for?? thanks

 

[rick]

i just recently had a problem with my talon, it wqas rising to 1500 then dropping to 1000 at idle. i adjust the biss, and it seems to helped, but its doing it again. i need to change the o2 sensor and plugs.

 

[1stGENracer]

My rpm's don't change that much, just a little bit, from 750 rpm's to 1000 rpm's.

 

[jw]

Originally posted by 1stGENracer

Also on my datalogger, the little Idle switch thing turns on when I push the throttle, and tunrs off when idling.

It looks like this when I'm on the throttle.

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and that TDC sensor thing is flashing on and off, doesn't stay steady on.

1G has a idle switch on the TB. If you look behind the TB, you will find it sticking up and you wont miss it. Try pull the connector off the switch, you will turn the idle switch constant on and the idle will go up around 1500rpm.

The TDC sensor should be flashing because the crank is rotating. When the CAS reads TDC, it will light up the TDC on the logger.

 

[IPT]

Check you intake for leaks. Do a pressure check. Also with as old as your car is you might want to think about checking and/or replacing the vaccum lines. I was amazed at how may of my lines in my 92' had samll holes in them.

 

[1stGENracer]

I alreay replaced a few lines, but I was going to do the rest.

 

[purplehazetsi]

my 91 tsi does the idle like that, but on hot days it will idle steady at 2 for a while then drop to 1500 then to 1000, but it could be your tps (throttle posistion sensor) or an idle motor! chech those out it could be them