2G Stumbling at hot startup

PlanZero · Feb 1, 2017

Ok here's another one. My GF has been daily driving the TSI AWD for several months, and about 75% of the time she (the car) stumbles and wants to die at a hot or warm start. It seems to be worse after a highway or longer trip. After about 30 seconds she's fine, and only once or twice did she actually die. Giving her some gas makes no difference. Originally I thought IAC because sometimes the idle bounces up and down, but after changing the IAC twice with known good ones it doesn't really help. I also put in an evoX fuel pump (worked great on my FWD, no difference on the AWD), and new fuel filter. The CTS is newer, and no problems on cold start.
This car is mostly stock, so I'm thinking possibly MAF. It doesn't appear damaged or dirty and I'm wary of using any cleaner. However, when I unplug the MAF she sounds much worse. I also tried examining and jiggling the wires on the plug since they're prone to breakage when she's acting up but still no difference.
I remember reading somewhere that this is common on DSMs, but I don't know if it was even a reliable source, and the few DSMers around here never had this problem.
Once I he weather breaks I was gonna go to the junkyard and grab a MAF (609) and plug off a galant and see if there's a difference.
Anything else I should check?

Zero6391 · Feb 1, 2017

so this only happens at start up? and only last 30 seconds? sounds like maybe front oxygen sensor

PlanZero · Feb 1, 2017

Yeah only on hot starts, and usually only when she's running kinda hard. I replaced the front O2 with a denso (OEM) about 6 months ago after I fried the wire running without a heat shield. No CELs except for egr since it's blocked off. This problem has been happening close to two years now, worse in the hotter months.
I also have an exhaust leak from a broken mani stud, which I plan to fix once it warms up. On my other Tsi I had 3 broken studs before the motor swap and never had issues, so I don't think that's it.

oneslowwdsm · Feb 1, 2017

Sounds to me like a throttle position sensor needs adjustment. There are proper ways of doing this but having DSMlink makes it much easier. Have you ever tried raising or lowering the idle via BISS screw?

PlanZero · Feb 1, 2017

Never thought a tps would cause these problems (you weren't answering my other post were you, oneslowdsm?), but I must emphasize I know way too much about calibrating the tps. I've replaced them many times, at least three times on this car. Since both my dsms are automatics, the tps plays a crucial role in telling the TCU when to shift. I also rebuilt the TB (with metal BISS) and deleted the FIAV.

2gmitsueclipse · Feb 1, 2017

Is the FPS still connected?

PlanZero · Feb 1, 2017

2gmitsueclipse said:
Is the FPS still connected?

Now that you mention it, the FPS is still connected. Perhaps it's malfunctioning? I'll try rerouting the hose tomorrow, or I can always swap it with my other DSM. The FPS is disconnected on my 96 and I never had any hot start issues, though my 97 is much more finicky all around.

Carlz0r · Feb 2, 2017

I had a CAS start to fail, it did what you described and eventually wouldn't start at all on hot starts (60-90 minute waits until one day it fully packed it in).

luv2rallye · Feb 2, 2017

FPS: http://www.dsmtuners.com/threads/vapor-lock-hot-start.217349/#post-1821514
Other possibilities: http://www.dsm.org/how-tos/JFM/HotStart.html

PlanZero · Feb 2, 2017

Thanks luv2rallye! No wonder that didn't come up when I searched.

I'm going to try the fps this weekend after I take her for a rip.

When I put the evoX pump in, the assembly looked fine and I used a new o ring. How could I even tell if the assembly was bad, as stated in the first link?

miliman13 · Feb 2, 2017

You know, you can test the maf with a multimeter...theres instructions in any of the repair manuals.

Better than throwing money at it.

PlanZero · Feb 2, 2017

Yeah I know, I'll try to do it this weekend. It's a PITA to work on this car because my gf dailies her and we work different shifts. Also, I've had two IACs and a TPS that all were in spec with a multimeter, but were definitely malfunctioning and corrected after I changed them. I needed to go to the junkyard anyway, so why not grab a spare for $10, plus a plethora of pocket parts.

miliman13 · Feb 2, 2017

^ to elaborate, with a heat gun or blow dryer. You heat up the maf and measure resistance. This will show if it's actually working when it gets hot. To eliminate your hot issue.

Detail · Apr 21, 2017

I've been struggling with this for a while. I pulled the fpr line today when it wouldn't start and nothing changed. This is really embarrassing. Anything else to try?

D

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2G Stumbling at hot startup

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