bureau13

Hmm, not sure. How does one read that?

ptuomov

MAF voltage, for example. Not familiar with the 86, but 87 S4 with sharktuner gives you MAF voltage.

If it can make a lot of torque by consuming a lot of air, it probably has to be a big leak and throttle position/linkage or cruise control would be suspects.

bureau13

Yeah it really feels more like a throttle linkage type issue rather than a leak, but everything seems fine to me. I can hear it click the idle switch when I release the rod after manually moving it. Maybe I should measure at the LH, but that throttle body plate does not appear stuck open, and the cruise cable is disconnected.

Adk46

bureau13

I believe you are correct, but I never removed the TPS from the throttle body, and the spring closing it is pretty strong. It was not held open when it was off the car... Is it possible something happened to it during reassembly? Maybe? Something to look at for sure... Action on the linkage feels normal but definitely something to consider

bureau13

I took off the air box, removed the MAF and felt around best I could. Nothing is obviously amiss. Put it back together, started it up...idling a bit over 2K. That's what it did before, and then when I started it up hot, it was at 3K. Maybe random, maybe related, who knows? Both wrong. I guess if I don't figure something else out by this weekend I will start working backwards and removing things until I find something odd. I have no idea what I will do if I DON'T find anything! At the very least, I should be able to leave the water bridge and oil fill tube alone. Right?? Maybe a good time to see if anything leaked, although it obviously hasn't been run much.

Question: If I pull the intake runners off again, do I need to buy another gasket?

bureau13

So I was bored and on a conference call that didn't require my full attention, and grumbling to myself about having to pull the intake off again, so I thought I'd do some more searching for idle issues. I found a thread where people were recommending blocking off various non-critical (for the engine) vacuum lines to rule them out, specifically brake booster, fuel vapor recovery, etc. This set off an alarm bell or two, because I just remembered something else I changed, that now reveals something I didn't change as a vulnerability. That little temp-controlled vacuum switch near the passenger side firewall? One of the nipples was broken off, so I had plugged it. It's been that way as long as I've owned the car. Now that I've replaced that broken switch with a shiny new one, I reconnected the vacuum lines properly. But what if that switch/cannister/whatever thing that it connects to has a leak? Might it not be leaking somewhere where I wouldn't necessarily see smoke?

Anyway, I have a few things to test. I'm optimistic!

bureau13

*&^%$#!

I blocked off the vacuum lines to both fuel vapor recovery switch things, blocked off the line at the T that leads to one of those fuel vapor recovery things and blocked off the leg of the Y connector that leads to the brake booster and HVAC vacuum controls. No change.

I disconnected the MAF electrical connector. Idle surges rhythmically, but still at about 2K.

I reconnected the MAF...btw both MAF o-rings are new and in place and stuck a vacuum gauge in the line that should go to the brake booster. About 18 inHg, which surprised me. With an apparent large leak, shouldn't that be much less? Or is this a case where the brake booster/HVAC vacuum can be wildly different than the other stuff? I seem to remember that happening in other vacuum leak cases. In any case, is this a clue about anything?

I give up. FOR SALE :-

Just kidding. Kind of. The thing is, I'll bet when the cause is finally found, it's something SOOO stupid....

bureau13

This thread has become my inner monologue. Should it somehow become disconnected from the forum as a whole, future generations who read it will determine that I was a crazy person. They may well be right.

I just noticed something while looking at a picture in another intake refresh thread: The two breather hoses from the PS cam cover had hose clamps on them at the cam cover. I have no such clamps, but it's entirely possible that I did before, and put them somewhere on reassembly that didn't actually require them. In fact, I think I did have them clamped before? In any case, it's a barbed fitting and the hose seems pretty tight. As tight or tighter as any of the vacuum lines in the seven way splitter, to be sure. Surely that is not something that would leak at a vacuum but not show anything during a low pressure smoke test?

Bertrand Daoust

Don't worry Jeff I'm sure many of us, like me, are looking at your thread but don't know exactly what the problem might be.

Just something I think of, are you sure that the throtle plate is well seated when closed?
Just saying...

With the idle that high, it would need to be a big leak. If this would even be possible. Can't say.
To me it seems to be something else.
But that's me.

I would first make sure, if you didn't already, that everything's good with the throtle cable, quadrant and throtle body.

Good luck.
I'm sure you'll find what the problem is.

bureau13

Thanks Bertrand! I'm just getting frustrated, as I miss driving this beast. Sorry about the whining

I agree, it seems like it would need to be a leak that is big enough that it's hard to hide. Before reassembly, the throttle plate seemed to be fully seated. I cleaned that area up, but I didn't disassemble that mechanism, or the TPS. I can't really see it now, but everything "feels" right when I manually move the throttle linkage back and forth. I've ordered one of those little phone boroscopes so I can try to see up in there without taking everything off.

I've been thinking more about the ISV. It's basically simulating a slightly opened throttle. What is the RPM if it fails fully open? I am guessing this is the situation when you jumper the diagnostic connector to remove LH idle control, and my recollection is that it jumps up a few hundred RPM, nothing drastic. Trying to work out if there's any way a failed ISV could cause this, other than via vacuum leak. Seems doubtful?

While I'm thinking about it, anyone know what the small threaded holes on the back of the plenum boxes are for? Nothing was attached there on my car. There are two screws loosely threaded there, I think by the powder coater to protect the threads...I don't remember them from before. NOTE: The holes do not go all the way through to the inside

bureau13

Here are a couple additional observations, in case something triggers an idea:

Vacuum from the line going to the brake booster is still at 19 in-Hg. Vacuum from one of the capped-off lines that is supposed to go to (I think) vapor recovery (not the one from the thermoswitch) is about 15 in-Hg. So, maybe vacuum leak? Yet I've had vacuum leaks that resulted in that reading which caused only marginally high idle. FWIW...

With engine off, I turned the idle screw all the way closed, then started the car. It ran and idled, around 1800. So, a bit lower than it has been, but if I understand this correctly, it shouldn't idle AT ALL with that closed off. Correct? Or do I need to jumper the ISV off to do this test?

With all non-essential vacuum ports capped, engine running, I gingerly sprayed some carb cleaner near the ISV, near the intake tube connections, and near the throttle body, injectors and even those breath tubes that aren't clamped....no discernible changes. I did this quickly, and not very well, because I'm paranoid. The engine heats up quickly at this speed and I really didn't want to deal with anything catching fire.

For now, I've removed the intake plenums, MAF and air box...peering around the tubes hasn't shown anything amiss...and I'm awaiting my boroscope, which should arrive tomorrow. I'm not pulling the rest of the intake until I've at least tried to snake that camera around everywhere to see what's what.

Mrmerlin

their is a very good chance the TPS unit is filled with oil

bureau13

Interesting... On what are you basing that? I didn't touch the TPS at all, I just cleaned the air guide and throttle body and replaced the o rings. It wasn't doing this before. Where would the oil come from?

Assuming that this is the case, I assume that's a symptom, not a cause. What is the solution?

bureau13

OK, I just went back and dug up some threads on this, it appears lots of folks had vacuum leaks through crunchy o-rings on the throttle body, which also leads to the TPS filling up with oil. Assuming I don't see anything obvious with the borescope, I will take a look at this when I disassemble. I've been operating under the idea that this must be something new, either something that I've done wrong, or something I've done right has now exercised a different area (e.g. the vapor recovery aft of the thermoswitch, since my old one was broken and blocked off). That said, maybe me having it apart and cleaning it up moved things around. Entirely possible.