# Bad hesitation under heavy boost - HELP, please!



## jtmorr01 (Feb 1, 2002)

hello all. i'm experiencing some persistent problems with my '01 s4 and was hoping for some help. when i'm in a high gear and hit the gas hard, the boost is all f'd up. it will start to go, then hesitate like crazy and sometimes act like it wants to shut down altogether. it's setting off my check engine light (it flashes during the first incident after being cleared, then stays on after that.) a recent code scan revealed a bad o2 sensor, so i just replaced that, hoping that might be the cause - nope! my mechanic suggested it could be the air flow sensor, but that is not showing up on the scan. my mechanic also performed a smoke test on the turbo system and everything was fine. any ideas? thoughts? sorry for the long post...


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## GLS-S4 (Jun 6, 2005)

*Re: Bad hesitation under heavy boost - HELP, please! (jtmorr01)*

I would suggest some VAG logging.
Could try log Block 114 N75 DC and 115 Boost Requested vs Actual while under boost
Watch for real time misfires under blocks 015 / 016 while driving, etc

Flashing CEL under boost can indicate overheating cats.
If CEL has been flashing for awhile under boost, forward metal substrate cats may be melted.


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## jtmorr01 (Feb 1, 2002)

*Re: Bad hesitation under heavy boost - HELP, please! (GLS-S4)*

Thanks. Regarding the overheating/melted cats, do I need to stop driving it? What are cats? (you lost me after VAG logging)


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## temagnus2004 (Mar 19, 2008)

*Re: Bad hesitation under heavy boost - HELP, please! (jtmorr01)*

The cats are catalytic converters. I had the same problem last month. We need VAG codes to determine a cause of action. My cure was replacing the EGT sensor - exhaust gas temperature sensor. Then the bucking went away and misfirings stopped.


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## jtmorr01 (Feb 1, 2002)

*Re: Bad hesitation under heavy boost - HELP, please! (temagnus2004)*

Thanks. I'll forward this info to my mechanic. By the way, how much did the EGT sensor set you back (parts and labor)?


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## jtmorr01 (Feb 1, 2002)

*Re: Bad hesitation under heavy boost - HELP, please! (temagnus2004)*

on another note...my mechanic did hook up some kind of code detection device to the terminal under the steering wheel. that's when the 02 sensor code was revealed, but no other code appeared. is that different from the vag code you are talking about?


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## temagnus2004 (Mar 19, 2008)

*Re: Bad hesitation under heavy boost - HELP, please! (jtmorr01)*

Replacing the EGT sensor and labor wasnt cheap - there are 2 - the bitch of the one is the one one drivers side right by the turbo_VERY tough to get to. It cost me around 660$ about 380 for sensor alone. The VAG com tool is referring to a cable that is also connected to obdII port. Cable is connected from car to laptop and is accessed via software. The Vag software will list EVERY damn code, misfire, fault you may have. Only a complete scan will give a direction to go with.


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## jtmorr01 (Feb 1, 2002)

*Re: Bad hesitation under heavy boost - HELP, please! (temagnus2004)*

$660! Ouch! But well worth no longer enduring this unreliable boost







...especially when passing semis in the winding hills of West Virginia.







Thanks again for your help, temagnus2004 and GLS-S4!


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## jtmorr01 (Feb 1, 2002)

*Re: Bad hesitation under heavy boost - HELP, please! (jtmorr01)*

hey everyone. just wanted to let you know that my shaky boost problem has been solved (knock on wood.) the vagcom revealed the code for a bad egt sensor. once it was replaced, the problem was gone - strong, reliable, boost is back, baby!
thanks to everyone for your help on this. i hope i can return the favor some day...
joel


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## nappent (Oct 16, 2003)

*Re: Bad hesitation under heavy boost - HELP, please! (jtmorr01)*

I having exact same problem right now... where you misfiring? and if so which cylinders? 
Right now I'm getting a misfire in cylinder #1. Just wondering if you had the same problem.


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## jtmorr01 (Feb 1, 2002)

*Re: Bad hesitation under heavy boost - HELP, please! (nappent)*

yes, i was misfiring...in all six cylinders.


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## KillA6 (Sep 19, 2008)

*Re: Bad hesitation under heavy boost - HELP, please! (jtmorr01)*

Mine did this when my EGT went bad. Also did that when my coil pack went bad. But my hesitation was more like a rapid firing machine gun of missfires. Another time I had an issue it was a spark plug. 
FYI sometimes it takes a little bit to get a bad EGT to throw a code even though its going bad.


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## 2035cc16v (May 18, 2000)

*Re: Bad hesitation under heavy boost - HELP, please! (temagnus2004)*


_Quote, originally posted by *temagnus2004* »_ My cure was replacing the EGT sensor - exhaust gas temperature sensor. Then the bucking went away and misfirings stopped. 

same problem and solution here... i have a brand new genuine audi EGT available for 200 shipped if you want it, i bought 2 and only needed 1.
email is vwms16v(at)gmail(dot)com


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## jtmorr01 (Feb 1, 2002)

*Re: Bad hesitation under heavy boost - HELP, please! (2035cc16v)*

well, unfortunately, my problems have returned. after replacing the egt sensor 2, i drove the car for a few days and the check engine light came on. i also started experiencing the same hesitation as before. i took it back to my mechanic and he hooked up the vag com again. this time, i am getting a code for the egt sensor 1. has this happened to anyone else? is this just a crazy coincidence that one would go bad immediately after the other one does? this whole boost problem is killing me and my wallet! thanks.


_Modified by jtmorr01 at 7:14 PM 11-18-2008_


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## temagnus2004 (Mar 19, 2008)

*Re: Bad hesitation under heavy boost - HELP, please! (jtmorr01)*

I am sorry to hear about the other EGT sensor going. For myself, this has not happened to me. I would like to say that this is indeed a coincidence.
My S4 has been running great with the k04's installed. What a beast, it has piggies and no cats. I am considering running resonators because I hate to say it but it might actually be a little too loud!! muhahaha


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## GLS-S4 (Jun 6, 2005)

*Re: Bad hesitation under heavy boost - HELP, please! (jtmorr01)*


_Quote, originally posted by *jtmorr01* »_well, unfortunately, my problems have returned. after replacing the egt sensor 2, i drove the car for a few days and the check engine light came on. i also started experiencing the same hesitation as before. i took it back to my mechanic and he hooked up the vag com again. this time, i am getting a code for the egt sensor 1. has this happened to anyone else?

Possible Coincidence or Inferior Fuel? Have you changed gas stations or fuel brands or decrease octane ratings recently?
Many people have reported multiple exhaust sensor failures in short time periods due to inferior fuels. Audi Service Reps report similar stories for their customer cars and suggest using reputable high octane fuel exclusively.
Other running issues could cause spiking exhaust over temps during extended boost cycles that can help shorten exhaust sensor life. VAG Logging EGT's under boost would be able to detect if it is an issue.


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## jtmorr01 (Feb 1, 2002)

*Re: Bad hesitation under heavy boost - HELP, please! (GLS-S4)*

i use 93 octane exclusively and patronize the bps, shells, etc. whenever possible, so i don't think that is the culprit.
what other running issues are you referring to?
thanks gls-s4...
joel


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## Werked (Jun 13, 2007)

*Re: Bad hesitation under heavy boost - HELP, please! (jtmorr01)*

Either your Check valve is bad or there is a tear in the intake boot on the throttle body.Also check the diverter valves.This should help.


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## buddylee401 (Oct 24, 2007)

*Re: Bad hesitation under heavy boost - HELP, please! (Werked)*

intake leaks, especially at throttle body can cause hesitations and choking sensations. also, for those with misfire codes.....anybody change the two ignition modules on top of the air box. there's a brown one and a black one. whichever cylinder you're getting misfire codes, coils and plugs not the issue, you can use a test light on the small modules on the air box. peel back the black rubber wiring harness connector and use the test light on the actual harness pins. if while the car is running, the test light blinks, it's all good. if it doesn't blink or doesn't light up at all, i'd bet that ignition module is the culprit. btw, pull back the rubber wiring harness connector on the side closest to the passenger side fender, not the side facing the motor.
i don't know if that's gonna help anybody, but i thought i'd throw it out there.


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## jtmorr01 (Feb 1, 2002)

*Re: Bad hesitation under heavy boost - HELP, please! (buddylee401)*

here's an update, for what it's worth...
things are as clear as mud regarding my hesitation problems. i took the s4 to my mechanic to have both the coolant temperature sensor egt sensor 1 replaced (both were throwing codes.) when it was discovered that the egt sensor 2 unit that i bought was going to require modifications to fit into the egt sensor 1 slot, i decided to just do the ct sensor and forgo the egt sensor 1 work.
now, everything is running great. no hesitation, no cel. why is the egt sensor 1 now behaving? it's the same one that was throwing codes and causing hesitation last week! could the failing ct sensor have been causing the problems? could it have been causing the egt sensor to think it was going bad? my mechanic did disconnect the (supposedly) failing egt sensor 1 in order to determine how my new egt sensor 2 was going to have to be modified - could there have been a loose connection that was remedied when he put it back in?
believe me, i am not complaining about not having to replace the egt sensor. i just want this issue resolved and to move on!
thanks.


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