Engine dies when coming to a stop or clutch pressed in and coasting
10-23-2018, 10:10 PM
#1
Rennlist Member
Thread Starter
Engine dies when coming to a stop or clutch pressed in and coasting
My 07 TT seems to have trouble with idling when coming to a stop or coasting. The revs fall below the desired idle rpm and then either 1) just fall to zero or 2) "catch" and rebound above idle and then settle in at idle. It doesn't do it every time, but it shouldn't do it at all.
Interestingly, the car does not do this if I clear all codes. The more it's driven thereafter, typically the more likely it is to have the issue. I've owned the car 10 months and it's always done it. I can drive around the problem by letting the revs drop slowly, but that's annoying too.
Car has 1000cc injectors and a custom 93 Cobb tune, but does the same thing if I use the Cobb OTS tune for the larger injectors. This leads me to believe there's something other than a bad tune leading to the issue. I've also pressure tested the intake with no issues identified. The car will throw an intermittent rear O2 code, but I'm not sure if that's related to my problem or the Tubi exhaust.
Any thoughts on what to check next? I have a Cobb, Durametric, and other more basic OBD loggers. Are there some common boost/vacuum leaks I'm missing? Failing MAF or O2?
Appreciate the help.
Interestingly, the car does not do this if I clear all codes. The more it's driven thereafter, typically the more likely it is to have the issue. I've owned the car 10 months and it's always done it. I can drive around the problem by letting the revs drop slowly, but that's annoying too.
Car has 1000cc injectors and a custom 93 Cobb tune, but does the same thing if I use the Cobb OTS tune for the larger injectors. This leads me to believe there's something other than a bad tune leading to the issue. I've also pressure tested the intake with no issues identified. The car will throw an intermittent rear O2 code, but I'm not sure if that's related to my problem or the Tubi exhaust.
Any thoughts on what to check next? I have a Cobb, Durametric, and other more basic OBD loggers. Are there some common boost/vacuum leaks I'm missing? Failing MAF or O2?
Appreciate the help.
10-23-2018, 10:34 PM
#2
Is it possible the car has a light weight flywheel installed? I have been debating whether to switch the factory dual mass flywheel for a lightweight version myself, during my research on the the topic I found those exact symptoms on others vehicles. The good news is it can be accounted for in the custom tune.
Kevin
Kevin
10-23-2018, 11:02 PM
#4
Three Wheelin'
My 07 TT seems to have trouble with idling when coming to a stop or coasting. The revs fall below the desired idle rpm and then either 1) just fall to zero or 2) "catch" and rebound above idle and then settle in at idle. It doesn't do it every time, but it shouldn't do it at all.
Interestingly, the car does not do this if I clear all codes. The more it's driven thereafter, typically the more likely it is to have the issue. I've owned the car 10 months and it's always done it. I can drive around the problem by letting the revs drop slowly, but that's annoying too.
Car has 1000cc injectors and a custom 93 Cobb tune, but does the same thing if I use the Cobb OTS tune for the larger injectors. This leads me to believe there's something other than a bad tune leading to the issue. I've also pressure tested the intake with no issues identified. The car will throw an intermittent rear O2 code, but I'm not sure if that's related to my problem or the Tubi exhaust.
Any thoughts on what to check next? I have a Cobb, Durametric, and other more basic OBD loggers. Are there some common boost/vacuum leaks I'm missing? Failing MAF or O2?
Appreciate the help.
Interestingly, the car does not do this if I clear all codes. The more it's driven thereafter, typically the more likely it is to have the issue. I've owned the car 10 months and it's always done it. I can drive around the problem by letting the revs drop slowly, but that's annoying too.
Car has 1000cc injectors and a custom 93 Cobb tune, but does the same thing if I use the Cobb OTS tune for the larger injectors. This leads me to believe there's something other than a bad tune leading to the issue. I've also pressure tested the intake with no issues identified. The car will throw an intermittent rear O2 code, but I'm not sure if that's related to my problem or the Tubi exhaust.
Any thoughts on what to check next? I have a Cobb, Durametric, and other more basic OBD loggers. Are there some common boost/vacuum leaks I'm missing? Failing MAF or O2?
Appreciate the help.
10-24-2018, 12:54 AM
#6
Rennlist Member
100% a tune issue. Mine did it on 93, but never once on the E85 mapping. Took some tweaking of a number of tables to solve. I actually saw the title, opened the thread, and looked immediately for where he mentioned ID1000cc injectors 
This is a common complaint with 1000cc owners, and something I haven't seen much with the 1300s. Not sure if there is an underlying hardware quirk that takes a bit more finesse with 1000s, or if there's just a more complete "dial-in" of the 1300s as these are what Cobb selected to develop their ethanol mapping on. I lean towards the latter.
This is a common complaint with 1000cc owners, and something I haven't seen much with the 1300s. Not sure if there is an underlying hardware quirk that takes a bit more finesse with 1000s, or if there's just a more complete "dial-in" of the 1300s as these are what Cobb selected to develop their ethanol mapping on. I lean towards the latter.
10-24-2018, 01:41 AM
#7
Rennlist Member
Thread Starter
No LWFW to my knowledge -- doesn't seem to rev any faster than I'd expect. It does have a Sachs 2.5 with the usual high, tricky clutch. Car has ~50k miles and is otherwise running great (save for the occasional rear O2 error).
To clarify, the car holds a steady idle -- what it fails to do is "catch" a falling idle when you depress the clutch after it's been driven (like when approaching a stop light or shifting very slowly w/o heel/toe). If it dies during a slow shift while moving, I'll pop the clutch to restart it. Once it's idling, it's rock steady. And you can blip the throttle or rev the engine from an idle without an issue -- that doesn't cause it to fail to "catch" -- it returns to idle fine. Thinking about it, I'm not sure I've tried to rev it in neutral and then depress the clutch and let off the gas (as you would when underway) -- I'll have to see if maybe that can trigger it -- I know the clutch switches do something to the way the engine runs.
Tune was my initial suspect too. But since I get the idle issue on all my tunes (Cobb 91, Cobb 93, Custom 93, Custom E85) and it goes away for several drive cycles after a DTC reset, I shifted my suspicion to something else (like an ECU adjustment to something like a leak or bad sensor). I wanted to rule out any physical issues before to resorting to coding around the issue. Before I retune, I may resort to replacing/baselining all the O2s and MAFs just to be sure.
Kevin (UMW): Any usual places for intake leaks, especially anything behind a check valve that won't show up on a boost test (which showed no issues)? I can boost test again just to be sure. I'll did some searching on the 996 fuel pump issue and most of what I found regarding the fuel pumps had an irregular idle, or difficulty holding any idle -- that's not exactly my symptom. Was that what you were referring to or something more like my situation?
To clarify, the car holds a steady idle -- what it fails to do is "catch" a falling idle when you depress the clutch after it's been driven (like when approaching a stop light or shifting very slowly w/o heel/toe). If it dies during a slow shift while moving, I'll pop the clutch to restart it. Once it's idling, it's rock steady. And you can blip the throttle or rev the engine from an idle without an issue -- that doesn't cause it to fail to "catch" -- it returns to idle fine. Thinking about it, I'm not sure I've tried to rev it in neutral and then depress the clutch and let off the gas (as you would when underway) -- I'll have to see if maybe that can trigger it -- I know the clutch switches do something to the way the engine runs.
Tune was my initial suspect too. But since I get the idle issue on all my tunes (Cobb 91, Cobb 93, Custom 93, Custom E85) and it goes away for several drive cycles after a DTC reset, I shifted my suspicion to something else (like an ECU adjustment to something like a leak or bad sensor). I wanted to rule out any physical issues before to resorting to coding around the issue. Before I retune, I may resort to replacing/baselining all the O2s and MAFs just to be sure.
Kevin (UMW): Any usual places for intake leaks, especially anything behind a check valve that won't show up on a boost test (which showed no issues)? I can boost test again just to be sure. I'll did some searching on the 996 fuel pump issue and most of what I found regarding the fuel pumps had an irregular idle, or difficulty holding any idle -- that's not exactly my symptom. Was that what you were referring to or something more like my situation?
Last edited by Brainz; 10-24-2018 at 02:09 AM.
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10-24-2018, 01:26 PM
#9
Rennlist Member
Not a bad idea to baseline your sensors, but there are multiple threads on this and my car 100% acted the same way. Zero hardware changes. If anything, spend the money to upgrade to 1300s and get the flashes for those. The reason my E85 didn’t do it is because it was built off a different base map without substantially different base fueling. The pump map built off the Cobb base mapping had this issue. Reach out to Mitch at Cobb. This isn’t a terribly uncommon issue and I’m sure he can get you sorted out.
10-24-2018, 04:53 PM
#10
10-24-2018, 09:28 PM
#11
Rennlist Member
Thread Starter
Thanks for the feedback. Will do some logs on MAFs, O2s and fuel trims when the car isn't idling right. Will also see what happens if I disconnect the MAFs.
Next step barring any interesting findings will be to replace the MAFs -- it's easy to do -- about the same as changing the air filter: Remove the Y-pipe on top of the engine. Loosen the clamps on the downstream side of the MAFs (where it connects to the pipes going to the turbos). Unclip the breather on the back of the left side of the airbox. Pull up on the airbox to remove it with the MAFs connected. Reassembly is the reverse.
Next step barring any interesting findings will be to replace the MAFs -- it's easy to do -- about the same as changing the air filter: Remove the Y-pipe on top of the engine. Loosen the clamps on the downstream side of the MAFs (where it connects to the pipes going to the turbos). Unclip the breather on the back of the left side of the airbox. Pull up on the airbox to remove it with the MAFs connected. Reassembly is the reverse.
10-25-2018, 03:12 PM
#12
Rennlist Member
Why do you need to remove the Y pipe? Just unscrew the two screws holding the MAF's in place and pull each out??
10-25-2018, 04:44 PM
#13
Rennlist Member
Thread Starter
Your post reminded me, however: The screws holding the MAF sensors to the MAF housings may have a special security screw -- I seem to recall that mine are a 5-pointed torx design. I need to order one of those bits...
10-26-2018, 12:41 PM
#14
Rennlist Member
Thread Starter
I found this link with confirms what NZskater said about being able to replace the MAF sensors with the Y-pipe installed.
Good reference for replacement or cleaning -- also says the security bit with 5-point Torx 25. https://bit.ly/2SjT6WN
Good reference for replacement or cleaning -- also says the security bit with 5-point Torx 25. https://bit.ly/2SjT6WN
10-26-2018, 03:18 PM
#15
Rennlist Member
That's the one. Need a Pentalobe (as apposed to a standard Torx) to remove it.