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I've posted about a couple things previously, searched threads where people had similar issues, etc. However, I was sort of thinking about these things one symptom at a time, and it occurs to me that if they're all related, they may set a lightbulb off in someone's head, seeing them all together. So here we go, if any lightbulbs go off, please let know! (I'm ignoring my no-start issue for now, because it's not happening, and was either fixed with relays or will come back at some point). Btw some things have been suggested for some of these symptoms individually, and I have or will try them, this is evaluate them together as a possible singular problem.
- Rough idle, especially when cold...it just doesn't seem smooth. I DEFINITELY need motor mounts, but it's not just the vibration, it just doesn't sound smooth.
- RPM drops almost to zero before returning to idle when driving...doesn't really do it sitting in the driveway in neutral, for some reason.
- When getting on it hard from about 3K to close to redline, sometimes it pulls super hard, sometimes it just seems to not have that same power, and others it will have that sluggish feel, and then it's like something catches and it surges up to that full power feeling.
- At light throttle, around 2K-3K, I often get a shudder or rhythmic surge, it feels very much like when you suck at shifting a manual, only in this case it can happen fully in gear...usually if I back off the throttle a bit and then give it more gas it goes away.
Do these sound like related items, or are they more likely separate issues?
TPS: check for click sound and for voltage/resistance at harness connector;
ISV: not aware of a good check, but can try the WD40 and monitor for any changes;
Also seems to me that fuel pressure could be in-play, erratic voltage to pump, faulty regulator, etc. Is the problem at start up constant, or intermittent like the high-demand variability?
Someone sharper can probably hone that down to a finer point, but usually the list of candidate problems gets longer, especially when diagnostic work isn't knocking off some candidate faults.
And case in point, hey some vac issue at the ecu could introduce variability into the timing, but the intermittency seems odd for that one.
Simple check- vac gauge on the line and try to emulate throttle demand.
Or, bad plug/coil wires...see how it goes....;-).. mist with spray bottle of water at night and watch for arcing, and inspect wires for chafing/wear/white marks and the surfaces they are on for indications of shorting to ground.
Regarding the TPS, I'm definitely getting the click. Still need to do the other check to see if the switch is actually working properly.
Here's an interesting tidbit on the history of my ISV: The PO was replacing all the aging vacuum lines in the intake area. The ISV looked OK so he sprayed some WD40 in there and left it alone. It's hard to say but I think both of the idle problems have been getting worse, which would make sense if I have an ISV that is on the way out. Brian (PO) suggested I spray some more into the vacuum line that connects to it (but where is that? I can't figure out where that is) and if it gets better, I'll know that's the issue.
I went to validate info was available via above, and noted the prevalence of success posts were for S4s, so take note of this, extracted from the "which hose" thread that comes up in the search results:
"FWIW the idle stabilizerthats being described works very differently on the 85/86 engines VS the 87 and newer
The 85 86 ISV is a wear item and spraying WD40 into it isnt going to fix a sticking issue.
NOTE the armature will wear down and the brushes will grind into it thus grabbing the armature and causing it stick.
The 87 and later can usually be freed up if its a corrosion issue.
Lol yeah yeah....but to be fair, most of those links with pictures or diagrams reference the '87+ cars. There were some pics of a half-dismantled S3 top end but I couldn't see the ISV or associated tube. There was a pretty good verbal description of where it is for an S4, if it's roughly the same on my car then I think I know where to look.
I should add perhaps that I replaced the distributor caps/rotors (made a big difference actually) but not the wires. I see no arcing at night but I'm sure that's not a definitive test. They're expensive so I didn't want to simply replace them "just because," and I didn't want to get cheap ones that are likely junk, but they are almost definitely the original wires (~87K miles). I'm almost thinking at that age, I should just shut up and replace them so I have a decent baseline in the ignition system.
Lol yeah yeah....but to be fair, most of those links with pictures or diagrams reference the '87+ cars. There were some pics of a half-dismantled S3 top end but I couldn't see the ISV or associated tube. There was a pretty good verbal description of where it is for an S4, if it's roughly the same on my car then I think I know where to look.
The ISV is located on the passenger side of the engine under the back side intakes. If you take the air box off and the MAF out, you can see it. To remove it though, you have to get to the worm/hose clamps and i think the only way is to remove the big center "T" intake over the throttle body. I'm not positive about it being the only way but, that's how I got to my ISV. Getting that center "T" intake back on the throttle body is a BEAR.
well, this is where, in some respects, the 85/86 intake is good, once you're down far enough you can loosen or remove isolated runners instead of the whole thing.
I agree that popping the "T" out without disturbing the runners is frustrating at first, finding the right combination of twists, tugs and petitions to the higher power of your choosing..getting back in is the reverse, but you have to zip a straight edge around the forward edge of the boot to get the center bore to seat.
All of this is manageable.....if the angles to loosen the clamps can be divined.
And you are probably right about the wires- like the fuel lines age and exposure can be cruel to the insulation. I didn't mean to impart that the visual inspection is determinative for sure, it's just a coarse check. Replacements are costly compared with some other cars but with some digging there is a decent continuum of pricepoints and quality levels.
Yikes, I have my airbox out (first time) and I can see neither the ISV nor the back-of-engine grounds. In any case, it seems like the WD-40 trick isn't such a great idea for the S3, based on the comments above. I'm going to keep poking around while I have the airbox out, but I honestly don't know how you guys get to some of this stuff.
Regarding the plug wires, here's a quick pic that shows what I'm seeing...I haven't found any obvious issues with the insulation or the ends, but this extra layer of insulation that abounds is mostly like this...all cracked and falling off. I don't think that in and of itself should be a problem, but it seems like pretty good evidence that they're pretty damn old.
for what it's worth, as far as the RPM drop. Mine would almost stall with a romp of the throttle, and then level off. I just did a intake refresh this spring. As far as the intake tubes go, they look more scary than they are to R&R. I found a vacuum line disconnected from the throttle body, and I took the ICV off, spayed it liberally with PB Blaster, and then sprayed a silicone lubricant in it and let it soak.
Something I did cured the idle/stall problem. Now when I romp the throttle it goes right back to idle RPM's without searching. Always take several pics before, during and after while doing a Intake R&R.
Oh, and as for the plug wires, I am sure yours are original by the looks of the pics. I also still have my original wires installed. Just be very careful as not to cause any stress to the wires.
12-04-2014, 10:32 PM
Rough idle and other symptoms
