Warm idle issues

[Mike F]

Hi everyone! It's been a while since I've posted here; hope everyone is doing well! I apologize ahead of time if this particular issue has been addressed, but I didn't really find something exactly like this during a search. For a while now, I have been having a warm idle issue. It runs and idles smoothly when cold, but once it warms up (presumably to the point where Lambda takes over), I get a very "cyclic" bad idle. It will idle fairly well, FV is buzzing, then the FV stops, dwell drops considerably, and it stumbles like it's going to die. Then FV starts again, idle goes up, and it's fairly smooth again. This happens continuously. See video below:


http://www.youtube.com/watch?v=8TtSp4IH_wA

Like I said, it's been doing this for a while, but as I haven't been driving the car that much it hasn't been something that I have really dug into. It did this before and after my VOD job, which included new plugs, wires, distro cap & rotor, silicone vacuum lines, and injector seals. Does this look like a mixture issue? I thought it may be, but before I started fiddling with the mixture screw I thought I'd run it by everyone here first. Thanks!

[DMC Fanatic]

My car does the same exact thing when it goes right from open loop to closed loop. With my car, it will swing and hunt like this until the engine starts to get hot, then the dwell will settle nicely fluctuating between about 35 - 45 degrees. When you start driving it, it will clear up sooner than letting it idle. Whats happening is the o2 sensor needs to be hot to start putting out a good signal. Did you let the car get hot enough to notice any change? How long did you let it idle for when you took this video?

[Bitsyncmaster]

Try pulling the idle motor connector when it's doing that and see if the dwell holds. It could be the really slow idle speed it not letting the O2 stay warm.

Another possibility is a restricted exhaust (plugged cat) which would also upset the O2 sensor.

[Elvis]

The mixture or signal (bad O2 Sensor? shorted cable ? pulled connector? ) is so far off,
that the Lambda ECU tries to control or compensate for it - but reaches the end/limit.
Then the ECU says - this must be wrong, this is not a valid condition - and starts over again
and jumps back to the starting position.


I don't know if it's too lean or too rich.
What I would do is - if I am sure there is no bad vacuum leak -try to adjust the mixture.

Mark the position where you started to turn the screw. Close the hole after adjusting it.
Do not turn that screw more than half a turn, I bet it's less than a quarter turn to bring it
in a good working condition. Usually you turn the screw 1/16 turn to adjust it, so please
stay within half a turn.

[Mike F]

My car does the same exact thing when it goes right from open loop to closed loop. With my car, it will swing and hunt like this until the engine starts to get hot, then the dwell will settle nicely fluctuating between about 35 - 45 degrees. When you start driving it, it will clear up sooner than letting it idle. Whats happening is the o2 sensor needs to be hot to start putting out a good signal. Did you let the car get hot enough to notice any change? How long did you let it idle for when you took this video?

For this particular video it had only been idling for ten minutes or so, but even when I drive it continues to do this. It never completely dies, and runs fine under power, but when I stop (red lights, etc.), it goes back to stumbling.



Try pulling the idle motor connector when it's doing that and see if the dwell holds. It could be the really slow idle speed it not letting the O2 stay warm.

Another possibility is a restricted exhaust (plugged cat) which would also upset the O2 sensor.

I'll try pulling the ISM connector and report back!

[DeLorean03]

That is practically identical to what my car did from 2004-2005. Could not stand it. Went open loop and had a pretty rock-solid steady idle up to this year.

[Mike F]

Ok, cranked her back up and got it warmed back up enough to let Lambda take over (didn't take long as I just had it running before I posted that video). Pulled the ISM connector, and no change.

[Elvis]

My car does the same exact thing when it goes right from open loop to closed loop. With my car, it will swing and hunt like this until the engine starts to get hot, then the dwell will settle nicely fluctuating between about 35 - 45 degrees. When you start driving it, it will clear up sooner than letting it idle. Whats happening is the o2 sensor needs to be hot to start putting out a good signal. Did you let the car get hot enough to notice any change? How long did you let it idle for when you took this video?


When cold the dwell should be steady - if not - then the temperature signal is faulty !

[DMC Fanatic]

I would try leaning it out a little about a quarter of a turn and see what happens. This will increase the dwell figure. Also, how old is your o2 sensor?

[Mike F]

When cold the dwell should be steady - if not - then the temperature signal is faulty !

Mine stays rock solid when cold.

[Elvis]

did you read my first post ?

[DMC Fanatic]

When I went into the VOD in my car and replaced the same components that you mentioned and assembled everything back together, my mixture ended up being a little off, so I had to readjust it. You probably have the same issue. Id also recheck the vacuum lines just in case.

[Mike F]

I would try leaning it out a little about a quarter of a turn and see what happens. This will increase the dwell figure. Also, how old is your o2 sensor?

I will give that a shot. I assume that would be counter-clockwise? Just want to make sure! As far as the O2 sensor, I have no idea. I have not changed it (had the car right at a year), and there's nothing in the records that came with the car (dating back to 1993) that indicate that it was changed since then.

[DMC Fanatic]

Yea counterclockwise

[Mike F]

did you read my first post ?

I did. I actually missed it the first time through; you guys respond fast! I'll try working on the mixture a bit. I was just hesitant to do it before I ran it by here first. I've heard quite a few horror stories about gung-ho mixture adjustments...

[Elvis]

Update ?

adjusting that screw takes only minutes :-)

[Mike F]

I'm turning it really, really slowly. :) Sorry, I should have posted that I had to pack it in after that last post. Haven't had the chance to get back out and work on it any more. I will see if I can get on it tomorrow. Thanks again for the help; I'll keep you posted!

[Mike F]

Finally managed to get in there and work on the mixture this afternoon. I think I still need to do a little more tweaking to get it just right, and I'll do that once I put some more gas in (she's running low and don't want to keep idling in the garage and run the risk of not making it to the gas station!). Wow, that sounds like such a dumb reason not to finish when I see it typed out... :) Anyway, things are significantly better now. It isn't dropping down like it wants to die anymore, and the meter is showing much more normal behavior now. Before, it wouldn't even get to the point where it was "bouncing" so that I could check the range. It's bouncing now, and other than the "upswing" going a little past the 45-degree mark, seems to be performing well. I'll work on it some more and see if I can get it dialed in tighter. Thanks again for everyone's help!

[DMC Fanatic]

Thats great to hear! Just a quick question - When your car immediately changes from open to closed loop, does the dwell swing at low numbers first until the engine gets hot then swings in the correct range? Or does it immediately start swinging from like 35 to 45 degrees? On my car the dwell swings a little low and erratic like in the video you posted then settles in nicely when hot.

[Mike F]

Thats great to hear! Just a quick question - When your car immediately changes from open to closed loop, does the dwell swing at low numbers first until the engine gets hot then swings in the correct range? Or does it immediately start swinging from like 35 to 45 degrees? On my car the dwell swings a little low and erratic like in the video you posted then settles in nicely when hot.

Well, I can't say that I have yet seen what it does immediately upon switchover from a cold start since dialing it in. I did, however, shut it down once I got it initially running well, and started it up a few minutes later. With that, it did not start swinging immediately in the proper range when it did the switchover. It went a bit low and then "caught up" a few seconds later and settled in. Seems like ours are both doing roughly the same thing.

[David T]

Well, I can't say that I have yet seen what it does immediately upon switchover from a cold start since dialing it in. I did, however, shut it down once I got it initially running well, and started it up a few minutes later. With that, it did not start swinging immediately in the proper range when it did the switchover. It went a bit low and then "caught up" a few seconds later and settled in. Seems like ours are both doing roughly the same thing.

If the car hasn't been running in closed loop for a long time and/or it has been running very rich it can take a while for the O2 sensor to start reacting correctly. In fact, it may never really work like it should and you may have to replace it.

[Mike F]

It is entirely possible that my O2 sensor is shot. Like I said before, records dating back to 1993 never show it having been replaced, and with the mixture having been obviously off a bit there's a definite chance that it may be fouled. My car has 46k on it, so it should have been replaced once (if you obey the lambda counter, anyway), but if it was I don't have any record of it. The PO kept pretty good records, so I suspect that if he had done it there would be proof.