whalebird

With the AFM off, be sure to test the intake air temp circuit. This wasn't mentioned in earlier posts, so disregard if it has been eliminated
Another approach is to perform the DME test plan layed out in the factory manuals. It measures everything at the control unit plug as opposed to each component individually.

rusnak

The intermittant symptoms are confusing. Vacuum leaks, depending on where they are, can cause intermittant symptoms, at least in my case. But a bad fuel pump, bad or leaky fp regulator, etc can also cause problems. You probably need to get out the test instruments. The dme test plan was posted a while back, and is vey good.

I think napa auto should be able to rent a co% meter to you. If you do buy an lm-1, you will have no problem re-selling it. You'd probably use it at each tune up, or smog inspection.

TroyN

BTW, having an on-board AFR meter is not a one-time-use thing. AFRs will fluctuate based on weather, temp, season, issues with your motor, ignition system, FI, etc. Having the meter will let you constantly monitor how everything's doing, all the time. It's fun to watch too.

A loaner CO meter will probably work only in the tailpipe, which is after the cat, so will not give you valid readings.

Without real-time AFR readings it's all speculation as to what's happening.

Droops83

It sounds like you are running lean, at least at idle if it runs best with the idle mixture screw all the way in. You say you had it checked for vacuum leaks. How? Was it smoke tested? Smoke testing is great, we use ours all the time, but I have found that it often will not pick up on the infamous intake manifold gasket leaks on the 3.2s. Check the torque of all the nuts and do the old fashioned carb or brake cleaner spray around the gaskets and see if the idle changes. How are the breather hoses? If you only had the intake system smoke tested, that doesn't take the breather system into account. Check fuel pressure as well, it is unlikely that it is the problem but always worth checking as part of a full diagnosis if everything else looks OK.

Does the engine run/idle any differently when warm with the O2 sensor disconnected? That will be a big clue. If the voltage is staying at 0.1V and not switching, that is another clue (though most basic DMMs are not fast enough to show an O2S switching, will usually show the average 0.5V, you need an oscilliscope to accurately test an O2 sensor). But, the bottom line is, you really need to check the idle mixture with at least a CO meter, or even better, a 5-gas analyzer to see what is going on. With a basic CO meter, you need to test it before the cat at the test port, but of course the plug is always rusted in there and if the head breaks off and you have to drill it out . . . if you have access to a professional grade 5-gas analyzer, it WILL accurately measure AFRs after the cat, we use ours all the time for this purpose. Of if you can get your hands on one of the aftermarket wideband setups you can plug it into the stock O2 sensor location. Just be sure to free air calibrate the sensor before you put it in.

Oh yeah make sure you check the idle switch on the TPS to make sure the DME knows that you are at idle---does the idle change when you disable the ICV by jumpering the test pins (which is done when you check base idle)?

I would check the basics before condemning the AFM; you at least need to know what your actual AFRs are.

Good luck.

Joe6pack

Well Droops – I think you are on to something. Last night, I did something I hadn’t done before. I checked for vacuum leaks with the engine cold and the O2 sensor unplugged. It seems that a couple of the intake runners may be the culprit. With engine warm, off idle I was getting 0.4-0.6 VDC at the O2 sensor. At idle, however, the reading would drop to 0.1 VDC and stay there. But, with the engine cold, I couldn’t get above 0.1 on the O2 sensor when revving the engine. Sooooo, I sprayed intake manifold cleaner around the base of the runners and on a couple of them, the idle changed. I had done this test before with starting fluid, but never really got a change. But, I had always done the test warm with the O2 sensor plugged in. My theory is that with the engine warm and off idle under load, the leak either seals itself (thermal expansion) or is so small that the DME can compensate. However a few seconds after stopping, the pressure drops and everything goes lean (you can actually see this on the multi-meter attached to the O2 sensor).

Tonight, I am going to re-torque the intake bolts to spec. And repeat my tests. Even if this doesn’t work, I am going to order some new gaskets from Pelican – can’t hurt. I really think I have it this time.

dshepp806

As to the AFM "wearing out mode": it is usually do to worn spots on the copper trace. The arm can be repositioned so that it contacts "fresh" copper throughout it's sweep. I've not done this but have read of many others who have. This repositioning (as I recall) DOES NOT involve any muching around with the spring. Spring adjustment is a completely different thing (the pros will chime).

None of the above is a reccomendation but just an answer to your post.

It does sound like your on your way addressing vacuum leaks.......

Best of luck,

Doyle

Joe6pack

Ok - I tightened up my intake bolts last night. Either my torque wrench is way off or they were way loose. Anyway, I'm still lean. Though I'm not really in the mood, it looks like I will be replacing the manifold gaskets this weekend. Which brings me to my next question. I have searched, and it appears that it is recommended to replace the gaskets dry. I have always used a thin bead of RTV red on Ford intake manifolds. In fact, it is a common practice to throw away the two end gaskets and use RTV only - that's what I do. If nothing else, the RTV holds things in place. What is the board's consensus on RTV and intake manifold gaskets?

Thanks,

whalebird

I too have done the RTV thing on domestic V8s. It conflicted with my intincts to use clean new gaskets on whatever I was wrenching. Laying a big glob of silicon just didn't set right with me...but thats how it's done. I wont even talk about a Rover V8 which I have had the misfortune of trying to get "right".
To answer your question, I suggest no RTV anywhere on the intake. In fact, nothing kills an O2 sensor faster than silicon. Install them dry. If anything, a touch of spray gasket adhesive may hold them in place for assembly. A major flag in the Porsche world is looking at a motor/trans and seeing a big glob of RTV somewhere. It makes one ask "who's been in here?".

Ed Hughes

I used a little Curil T.

Joe6pack

How about aluminum paint on head gaskets. I have never understood that one although I have always done it without fail. Certainly doesn't seem to do any harm.

I can see where using a lot of silicon on the intake gaskets would be frowned upon, but I would think that a little wouldn't hurt and could help since these things seem to be such a source of problems. Done correctly, it should be a positive.

Droops83

Joe,

There is no need for silicone on these. Do them dry, or if you must, use a little Curil-T like Ed suggested (that is great stuff, always use it on chain cover/housing gaskets). The reason these gaskets leak is the barrel nuts that hold the manifolds on loosen up over the years. You will likely find the narrow parts of each gasket warped.

While you have the manifolds off, replace the fuel feed hose assembly that runs underneath the intake and goes to the fuel rails. Even if it looks fine now, it will leak at some point and be a fire hazard and it is a lot easier to do with the manifolds off.

Even after you do this repair, you should try to get you hands on some sort of CO meter/wideband O2 sensor and make sure you set the mixture accurately.

Ed Hughes

Curil T smells minty fresh too!

Joe6pack

Thanks - I always have this fear that one day I will look in my rear view mirror and see flames.

I'm thinking of asking Santa for a LC-1 or an LM-1.

whalebird

Been there - done that (In a VW beatle)...ALWAYS carry a fire extinguisher in your car. If nothing else, a small cheap one from a marine supply store.
Maybe Santa would bring me an LM-1 too. Group buy??

rusnak

Atta boy, an LM-1 will be an invaluable tool.

To rehash, the afm can be checked with a 9 volt battery (see other thread). If the idle does not drop when the oil cap is removed, then you might have vacuum leaks. Check the intake and crankcase hoses with a strong flashlight and inspection mirror. Take the airbox and afm out. Check the brake booster hose as it turns next to the firewall bulkhead and trace it to the mc booster.