Ed Hughes

I may take back my suggestion on vacuum in my post 8. I'd think that would be a constant problem- not something that kicks in like that. But, there are smarter people than me. I'd think either the ICV is hanging up or there is something happening with fuel. I also questioned in post 8 if the ICV has been cleaned-has it? That is simple and easy, and would be #1 in my mind.

Joe6pack

The ICV is clean and functions per the Bentley Manual. I have also swapped in a known good ICV (borrowed from Rusnak) and got the same results.

dshepp806

+1,...also get the LM to test mixture.

I burnished my copper trace , when I had the AFM cover off,..then cleaned it up,..then applied my noraml (audio!) Caig products. Although I didn't see any additional wear in the area of idle positioning (I was told to closely check this), decided no need to attempt a MOVE of the wiper arm contact postion but many have improved response by doing so......a connectivity thing, as you would imagine.

Was the O2 sensor changed?

Best,

Doyle

Ed Hughes

You really need to spell out what exacty you've done on these diagnosis request threads. I don't see that you posted that before. You did state that you replaced the O2 sensor, in response to Doyle's question above.

Joe6pack

Ok, here goes - Cleaned and checked ICV. Replaced cap, rotor, fuel filter, plugs, coil, CHT sensor and O2 sensor. Cleaned all grounds. Checked and cleaned afm. Cleaned intake using intake cleaner. Checked for vacuum leaks. Checked all wiring. Played around with mixture and set idle each time per Bentley manual. Best idle mixture seems to be full rich. Don't have an LM-1, so I've been using the narrow band O2 sensor. Can't get it any better than 0.1 VDC at idle. Runs great except for this little blip. Something is changing about 15 seconds after letting the idle drop back down. It is very repeatable and seems electrical in nature.

I just went out and ran the same route I ran earlier today with the O2 sensor unplugged. The base idle was lower, but it did not exhibit the drop in the videos. I had observed this behavior previously and that's why I changed the O2 sensor. So, my theory is that 15 seconds after getting off the gas, it is going into open loop mode. Why? I saw in one of the catalogs there is something called and Oxygen Sensor Relay. Anyone know anything about this relay?

Thanks for all the help. I know I am a pain in the butt, but I love problem solving and maybe this will help someone in the future.

Joe6pack

Ok, looking at the wiring diagram in the Bentley manual, there doesn't appear to be an oxygen sensor relay on '84-'89 cars even though Pelican shows one. If I am reading the diagram right, the oxygen sensor goes straight into the DME. Boy, I hope this isn't a DME problem.

TroyN

Those vids sure helped, your problem is not at all what I was thinking originally. It looks like the basics are in order, otherwise you probably wouldn't have such a steady idle. It sounds like it's popping a little though, which suggests to me it's running on the lean side (I know under certain cases it can pop when rich too).

In one of the other linked threads, I think, it talked about being able to check voltage readings at the ICV while it's plugged in, maybe try that. Hate to say it but having the wide-band O2 (you can get one from AEM which while not as nice as the LM1, does the job - I have one in my turbo and two in my race car) will probably shed a lot of light on how your car is set and what it's doing when it goes into low idle.

How do you get it out of low idle, can you do it while just sitting?

It almost sounded like the AC compressor (if you still have one!) was engaging, maybe another vid at the engine compartment is in order.

Joe6pack

Yes, it does pop with the O2 sensor plugged in. With it unplugged, the idle drops and the popping goes away. When taking voltage readings off of the O2 sensor, I can get it no better than 0.1 VDC. The afm is full rich. That's why I am wondering if I can get a little more adjustment out of the afm by changing the internal settings to tighten up the spring. Maybe the O2 sensor is reading lean at idle and the DME is shifing to open loop because the sensor isn't really sending it anything. Just a theory. I suppose one other option is to starve the air intake for air. Restricting air intake should richen the mixture at idle. I am at work now, but I may try that tonight.

dshepp806

I'd be extra careful if deciding to touch that spring...I've read somewhere that this baby is everso carefully calibrated (somehow).....and very easy to frick up.....moving the wiper arm to fresh copper isn't so much an issue.

Just an FYI.

Best,

Doyle

Joe6pack

I don't want to touch it without someone with knowledge addressing it. I have read that afms wear out, but I 'm not sure about the failure mode - i.e. do the springs weaken over time. I know that I am out of adjustment.

rusnak

Your O2 sensor seems to be working well, that is what brings the idle back up- I would guess. I think you have a lean condition, brought on by low fuel pressure or a vacuum leak I would also guess. You really should use a fuel air meter to do these adjustments.

The drop in idle looks exactly like the lean-stop test, which is to remove the oil cap while idling a fully warm motor with the o2 sensor hooked up. You can observe the mixture go lean, then return to normal as the injector pulses are lengthened. It takes a moment, just as in your video. I would hook up a fuel gauge and rent a co% meter if you can't find a F/AR meter. Vacuum is not constant you might have a hard to find vacuum leak. Have you traced the brake booster hose? There is a bend I believe near the firewall that is a biotch to find.

The other parts are tune up parts, and don't affect fuel air delivery. I think your dme is going to turn out to be ok.

Joe6pack

10-4. I just read an old thread you were involved in involving a bad afm and a rich condition. I may pull the afm again tonight (I'm getting good at it) and do the 9 volt battery test. I agree on the lean condition. I have checked for vacuum leaks several times, but I may give it one more go. I have not checked fuel pressure, but I may give that a go if nothing else pans out.

I can't seem to find an F/AR meter or co% meter for rent around here. I have considered buying an LM-1 or LC-1, but it seems like a lot of money for something I will use once.

rusnak

Joe, if you want, I can let you borrow my air flow meter from my '84 to use for diagnostic purposes. Just send it back whenever you're done using it. It passed smog not long ago, and it's sitting on the motor, which is waiting to go back into the car. I can just pull it and send it to you.

It fluctuates from .97 to 1.03 lambda, which works very well. And I won't need it soon (got spares somewhere).

Ed Hughes

I still would question what would cause a vacuum leak to "kick in" like that? It seems something is physically happening, and it isn't instantaneous.

Joe6pack

Hi Ed, yes, that's what has made this so hard to diagnose. As I said in an earlier post, coming off throttle, the idle is fine. It takes about 15-30 seconds before the idle drops. Using my DMM and the O2 sensor, I can see about 0.1 VDC at idle. Revving the engine it goes up to about +/- 0.5 VDC (I may film this and post another vid). I still think the O2 sensor is dropping out due to a lean condition which is causing the DME to switch to a default mapping. And, I can't richen the mixture because I am out of adjustment on the AFM. So, its back to looking for vacuum leaks, the aforementioned low fuel pressure or the faulty AFM.

Russ - Thanks for the offer, but you have already done too much with loaning me your ICV way back when I started this odyssey. Let me continue to play with this a little longer. If I can't get anywhere, I may take you up on the offer at a later time.

Thanks.