What did you do to your MK6 today?

[MrFancypants]

Yeah.

Any idea how the thing works? If it functions something like a fancy automatic “choke” system I can definitely see that being my problem. The way the car finally decides to drop to idle has a distinctly mechanical feel to it, like something had just decided to snap into the place it’s supposed to be after hanging the revs for a few seconds.

 

[Knotical]

Any idea how the thing works? If it functions something like a fancy automatic “choke” system I can definitely see that being my problem. The way the car finally decides to drop to idle has a distinctly mechanical feel to it, like something had just decided to snap into the place it’s supposed to be after hanging the revs for a few seconds.

I believe it uses a vacuum actuated arm to set the flaps to one of two positions. One position directs all the air to one side of those "blades" in the intake runner, basically cutting the port in half vertically to promote tumbling. The other position drops the flaps out of the way, allowing use of the entire intake port.

 

[MrFancypants]

I believe it uses a vacuum actuated arm to set the flaps to one of two positions. One position directs all the air to one side of those "blades" in the intake runner, basically cutting the port in half vertically to promote tumbling. The other position drops the flaps out of the way, allowing use of the entire intake port.

Ah ok then I’m guessing that’s not what’s going on.

 

[jay745]

Now I've got a new problem... now the car won't gently fall into idle after coming to a stop or revving the engine. It'll drop to about 1200 RPMs, sit there too long, increase in idle a bit occasionally spending a lot of time at 1500 RPMs, then it'll drop down to normal idle with a "snap." The longer it sits at an elevated idle the more it seems to want to quickly correct and send it down to the normal idle. Idle is smooth and fine when it gets down to it, no extra vibrations or weird noises.

How is the idle regulated on these cars? Can the bad spark plug cause this?

This is why I have trust issues with other mechanics touching my car. Maybe I should have just did the valve cleaning myself.

That's a clear symptom of a vacuum leak

 

[MrFancypants]

That's a clear symptom of a vacuum leak

Yeah that was my first thought but nothing obvious jumped out at me. I chose not to do any digging around the manifold because I’d rather not mess with work someone else did and then have to try to explain to them why I was poking around when I bring it back to them.

 

[Alpinee30]

That's a clear symptom of a vacuum leak.

This Id smoke check it you have to have a leak. Is you manifold the newest revision? High idle is a signal of an Air leak after MAF. Have you looked at fuel Trims?

 

[MrFancypants]

This Id smoke check it you have to have a leak. Is you manifold the newest revision? High idle is a signal of an Air leak after MAF. Have you looked at fuel Trims?

A new manifold was installed in 2017 or 2018, so I believe it’s of a new enough revision that it’s not prone to its original mode of failure.

I was busy working through the ignition issues yesterday so I didn’t observe fuel trims or do a smoke test.

Right now the plan is to get the new spark plugs in to eliminate that as a possibility (although I’m convinced you all are right and it’s a post MAF air/vacuum leak) and take it back to the shop that did the valve cleaning as I don’t have the ability to do a smoke test (need tools).

 

[MrFancypants]

New clue, threw a code this morning: P0441, EVAP emissions control system, purge valve

So it's a vacuum leak or a pinched line or something. I pulled the gas cap while the car was running to see what would happen and the idle immediately went to shit, so it's not that.

 

[MrFancypants]

Filled up my gas tank and now the car won't start. Fuck.

 

[MrFancypants]

Ok I managed to get it started by pulsing the throttle. But it runs like shit.

*edit* to avoid turning this thread into a live stream I’ll just edit this post…

I came across some knowledge about how the evap system works. Basically as you fill the gas tank vapors are stored in the charcoal canister. After filling up the purge valve opens and releases those vapors into the engine and pulls fresh air into the canister to clean the charcoal.

If the purge valve is stuck open those vapors aren’t trapped in the charcoal canister, but instead allowing those fuel vapors to fill the engine, effectively flooding it… causing it to run like crap until those vapors are cleared up. I also have to assume that the reason I’m getting some rev hang as the engine falls to idle might have to do with this valve being stuck open and not controlling those fuel vapors.

So the problem is in the evap system somewhere.

 

[brat_burner]

Yea and that purge valve is in the engine bay or should be

 

[king1138]

Ok I managed to get it started by pulsing the throttle. But it runs like shit.

*edit* to avoid turning this thread into a live stream I’ll just edit this post…

I came across some knowledge about how the evap system works. Basically as you fill the gas tank vapors are stored in the charcoal canister. After filling up the purge valve opens and releases those vapors into the engine and pulls fresh air into the canister to clean the charcoal.

If the purge valve is stuck open those vapors aren’t trapped in the charcoal canister, but instead allowing those fuel vapors to fill the engine, effectively flooding it… causing it to run like crap until those vapors are cleared up. I also have to assume that the reason I’m getting some rev hang as the engine falls to idle might have to do with this valve being stuck open and not controlling those fuel vapors.

So the problem is in the evap system somewhere.

Sounds to me like your EVAP purge valve failed. That would cause all of those symptoms, and they are pretty common to fail in the stuck open (or partially open) position.

 

[MrFancypants]

Sounds to me like your EVAP purge valve failed. That would cause all of those symptoms, and they are pretty common to fail in the stuck open (or partially open) position.

Yeah and what’s frustrating about that is the hose that’s basically glued on that, as far as I can tell, can’t be dealt with without pulling the intake manifold.

I found a tip that I can just cut the line and patch in a new line on the new valve, which I believe I’ll be doing.

Also wtf why am I having all of these issues all at the same time?

Good news is that after banging in the spark plug with the .70 gap the car stopped misfiring. I’m sure it’ll drive great when I get the new plugs in.

 

[speeding_ant]

Yeah and what’s frustrating about that is the hose that’s basically glued on that, as far as I can tell, can’t be dealt with without pulling the intake manifold.

I found a tip that I can just cut the line and patch in a new line on the new valve, which I believe I’ll be doing.

Also wtf why am I having all of these issues all at the same time?

Good news is that after banging in the spark plug with the .70 gap the car stopped misfiring. I’m sure it’ll drive great when I get the new plugs in.

Yeah, I tried that with ours and it wasn't 100% successful. Annoying that they glued it. I'd patch it with something full of resin, is strong, and overlaps the tube a lot.

 

[MrFancypants]

Yeah, I tried that with ours and it wasn't 100% successful. Annoying that they glued it. I'd patch it with something full of resin, is strong, and overlaps the tube a lot.

Yeah I'm not so worried about the hose to valve connection, that seems like a good hose clamp would work. For the hose butt joint I thought I'd use a lot of overlap and smear some variation of JB Weld on the inner tube before I insert it. I can't imagine an inch of overlap with an epoxy/resin seal would be problematic.

The rev hang is gone now, it's back to normal idle with no surging. So I guess yanking on the hoses and unplugging and plugging the thing back in did something. I still ordered a new valve though.