Stubborn to Idle with Clutch In

[Aaronbrook37]

Hey guys,

My B6T is acting up again. Can't catch a break with this motor... so I'm hoping there's an easy fix to what I have wrong. When starting the car cold, it won't hold an idle either period or for more than about 5-10 seconds. It can also at times be very difficult to start: requiring dozens of cranks and about a minute to get it going. Occasionally though, it'll hold a perfect 850-900 idle and let me get on my way. Later in the voyage, the engine rpm will drop the second I put the clutch in, and it'll hover around 500 for a few seconds before stalling if I don't catch and save it with the throttle. The same is true regardless of speed, revs, gear, or load on the motor. Then, even later in my test drive, it started to idle perfectly again. So it seems like 50/50 when it will idle and won't. When it does die on me, it'll start right back up with no issues. Here's what I've checked or replaced in the past little while:

TL;DR - Car won't idle when I stick the clutch in while driving.

Spark plugs and wires are brand new. Fuel pump, fuel filter, battery, distributor cap, and rotor have 3000 miles on them. Motor rebuild has 3000 miles on it. ISC has been replaced this week, and BISS screw is in the correct position. No vacuum leaks are apparent, and all silicone couplers are tight. No irregular noises coming from the engine bay at all. Battery is charged, serpentine belt is new, and alternator is working as intended. No lights on the dashboard indicating trouble.

Could my ECU be causing problems? It's the one thing I haven't even thought of throughout everything and it could very well be damaged.

Thanks all,

Aaron

[koRnhead]

Are you vented to the atmosphere with your BOV?

[Aaronbrook37]

I'm currently not running a blow off valve because I couldn't get the flange made up in time to get it on the motor swap. As such, the intake is sealed off on both ends for now. It hasn't posed a problem for the past four months... could it be coming back from the dead with a vengeance for me not having one?

[Movin]

Wires bad to the ISC ?

[koRnhead]

Depends on how much boost you are running. If its under 7 pounds you should be fine. Over and your throttle body will hate you.

[Aaronbrook37]

Depends on how much boost you are running. If its under 7 pounds you should be fine. Over and your throttle body will hate you.

Hmm well I'm running stock boost on a slightly larger turbo. Any reason it wouldn't cause problems for a few months first? I suspect it may be something else, but this could certainly contribute.

[koRnhead]

Remember your wastegate doesn't release the air that is already in the pipes. Just stops it from making further boost. Hence the need for a BOV. On low boost ie 7 and less the throttle body usually can handle the pressure. But at some point the seals give up and or you bend the throttle plate. Not saying this has already happened to you. But I would look over your TB real well and get that flange welded up.

[Aaronbrook37]

Oh wow I didn't realize it could do that much damage... I figured it only injured the turbo, not the throttle body as well. Thanks for letting me know, Kornhead. I'm going to be swapping blocks in the next couple weeks, and I'll be sure to switch out the throttle body if it appears to be damaged. It would certainly explain the issue. I'll also ensure to get the BOV on there to prevent further damage! Yikes... glad I caught this before it was too late. Appreciate it, good sir.

[blkfordsedan]

Is the IAC clean and functioning properly? My only other guesses would be the VAF meter, ignition module or a lose wire somewhere.

[koRnhead]

Not a problem.....and you are correct your turbo isn't exactly meant to hold pressure as well with the throttle plate closed. While it may not be the whole issue. It certainly will be a factor.

[rbrown]

I am with blkfordsedan, IAC. I think they call it ISC on the B6T. Also the BAC valve is related to this circuit. Sounds like they are not reacting properly to temperatures any more.

[FestYboy]

BAC... Blood Alcahol Content?

[rbrown]

BAC... Blood Alcahol Content?

lol Yeah that could be an issue as well.

[Aaronbrook37]

Well, I took a good look over the car and spent a little time working on it trying to sort out the issues at hand. Here's what I accomplished:

1. Rebuilt my intercooler piping completely from air filter to throttle body, finding a loose crooked fit on the compressor outlet. (nice big leak!)
2. Cleaned out the throttle body, which was a little dirty and sticky.
3. Sprayed out the ISC again with cleaner and some black/brownish gunk came out. I've done this two times now.
4. Charged up the battery, checked the plug gaps again, and dried out the entire ignition just in case.
5. Checked and cleaned up the O2 Sensor, the ISC wiring, and the TPS wiring. The ISC wiring was super cruddy and corroded.

And I think everything helped a little bit. The car pulls much more responsively and almost wants to idle now. It'll still stall with the clutch in or in neutral, but it takes a few seconds usually to do so. I reset the BISS screw now that my major air leak is gone, but it didn't help the issue. It also still has the starting issue where it'll take 10 times cranking the key to get it going after it stalls out the first or second time starting (which are easy starts). Was really hoping it would be something simple, but it may be more complicated than I had hoped.

[Aaronbrook37]

http://www.youtube.com/watch?v=kHb2yEfU6u0&feature=youtu.be