Continuing idle problems...

[s1ngletracker]

I have a basically stock 93 tsi, other than an axleback exhaust, which is why this problem is so pronounced and noticeable. Stock boost, all emissions equipment still intact.

I just did a boost leak, eliminated a few leaks (other than one that appears to be ON the compressor housing). I blocked the FIAV, I just replaced my ISC with a known good one. TPS tested and looked good. Throttle switch also tested and checked out. Looked at the caps in the ECU, no leaks at all. New paper air filter.

2 things: When I am rolling out of gear, the idle lopes, between about 1100 RPM and 1500, bounces back and forth about once every second or two. When I come to a full stop, it will slowly settle to about 1100 RPM. So that's interesting.

Also, the idle is just a bit rough, not really smooth and steady. This becomes very obvious with the louder exhaust.

Any suggestions for what to look at next?

[Kevin 1G Drummer]

My car does the same idle surge thing you were talking about, but I haven't really looked into it too much yet.

[Halon]

mine does that same bounce when rolling in nuetral sometimes, but settles when i stop. I figure it's because I have my car setup to idle at 1000. If your car is mostly stock, why are you idling at 1100? You should be closer to like 750 or so. Have you tried re-setting your idle? There's a VFAQ on the proper way to do it.

[iceminion]

Rolling=VSS spinning=IAC trying to keep idle higher
stopped=VSS stopped=IAC back to 700RPM

Just because you replaced your IAC with a "known good" one doesnt mean your IAC motor drivers on your ECU are any good.

FIAV has nothing to do with idle surge because it is all metered air anyways.

If you have your PCV system modified so that it is sucking un-metered air into the car, that would explain it.

The beauty of DSM's with stock MAF's is that they ALWAYS work great while in vacuum.

Good luck, tell us what fixed it.

[asshanson]

FIAV has nothing to do with idle surge because it is all metered air anyways.

I disagree. When I installed my SMIM I couldn't hook up my coolant lines because of the new location, and it idle surged badly. I blocked it off and it idles fine now. But that's probably not his problem because he said he already blocked off the FIAV.

[s1ngletracker]

an update...

I've been messing around with the BISS screw. I am able to actually kill that higher, loping idle to where once warmed up, it idles around 850 or 900 and doesnt lope. However, then when I shut the car off and try to start it after sitting a while, it won't idle initially. Even when the coolant temp is still high. I also get a strong smell of gas in this situation. So i'm basically even more confused now.

[s1ngletracker]

Rolling=VSS spinning=IAC trying to keep idle higher
stopped=VSS stopped=IAC back to 700RPM

Just because you replaced your IAC with a "known good" one doesnt mean your IAC motor drivers on your ECU are any good.

FIAV has nothing to do with idle surge because it is all metered air anyways.

If you have your PCV system modified so that it is sucking un-metered air into the car, that would explain it.

The beauty of DSM's with stock MAF's is that they ALWAYS work great while in vacuum.

Good luck, tell us what fixed it.

PCV system is completely stock.

[s1ngletracker]

I'm starting to suspect my BOV is bad. I can hear it leaking boost out once I hit a certain boost level (stock boost). Its like the squeak, whoosh sound you hear when you let off the throttle, except I can hear it on WOT. Could this be causing any other weird consequences that I'm not thinking of?

[Kevin 1G Drummer]

If your BOV is leaking, it won't make much difference if it's recirculated, unless it's leaking through the flange.

On a side note, now that it has been warmer lately, my car has stopped the idle surging when coasting in neutral. So I think my issue was related to the GM airflow sensor.

[s1ngletracker]

I've done a bit more work. I found some leaks in the throttle shaft O-rings, those have been replaced. I crushed my BOV a bit and tested it, it isn't leaking. I tested the wires, the resistances all look good.

I've gotten rid of any loping, my idle is stable and at a decent RPM. The reamaining problem i'm having is that the idle is just rough! It idles like it has a high lift cam, and it doesn't, if that makes any sense. It makes the car shake noticeably at idle. If i set the idle too low, it shakes even more and almost seems to struggle to idle.

Should I start looking into like the oxygen sensor? Coolant temp sensor? Try another MAF? I'm not getting any check engine lights.

Anyone know what to look at for this?