Part throttle stumble.. Baffled...

Spinnetti · 05-10-2012, 02:14 PM

1999 B5 1.8tqm 260k mi

Wasn't running great, with a full load stumble. Replaced plugs and coil packs, and stumble went away. I can floor it in 5th at 20 mph and it just pulls gently away. Anything less than WOT it hesitates. What could cause that? I replaced the MAF (twice) and the Throttle body is new too. I ran injector cleaner though thinking leaky injector, but it had no impact. I have a test pipe and fresh turbo too. After this many miles, should I replace the injectors? Is it a waste to have them cleaned? (Any DYI?)

thanks.

4Driver4 · 05-10-2012, 04:21 PM

Did you do a throttle body adaptation with the new throttle body? That would be step one.

Prospeeder · 05-10-2012, 05:52 PM

Temp sensor will cause alot of problems. Did you use NGK or Bosch plugs? no Air leaks or boost leaks? Codes? EPC light?

Spinnetti · 05-11-2012, 03:29 AM

Quote:

Originally Posted by Prospeeder

Temp sensor will cause alot of problems. Did you use NGK or Bosch plugs? no Air leaks or boost leaks? Codes? EPC light?

Can't seem to find air or boost leaks. I did throttle body adaptation with the vag. Denso iridiums (which I also us in my B6 and Touareg). No codes or lights other than o2 sensor

mtroxel · 05-11-2012, 04:29 AM

Quote:

Originally Posted by Prospeeder

Temp sensor will cause alot of problems.

that fixed my stumble too, new Coolant Temp Sensor.

Spinnetti · 05-11-2012, 02:52 PM

Quote:

Originally Posted by mtroxel

that fixed my stumble too, new Coolant Temp Sensor.

Worth a whack... I need to check - I thought I changed that too, but that might have been my B6.. hard to keep all this VAG stuff straight!

**RallyVermont** · 05-22-2012, 09:49 AM

Check your "L" hose from the back of the intake manifold.. this is known to leak and cause mystery boost issues, throttle hesitation etc... also if disconnected you'll lose your brakes. FYI - take a peek.

Spinnetti · 05-27-2012, 05:01 AM

Vac hoses all look good. Coolant temp sensor didn't do it, but it was like $6, so why not right?

Still have the part throttle stumble. Full throttle is fine, just part. Maybe I'll try adaptation again.

One other thing it does, when you abruptly let off the gas under boost, it doesn't just bypass "cleanly".. diverter valve? is fluttering.. I presume the waste gate can't flutter, but it sounds funny. not sure how to describe it. I have a B6 too, and it doesn't do that.

M.S.G. · 05-27-2012, 06:34 PM

Quote:

Originally Posted by Spinnetti

Can't seem to find air or boost leaks. I did throttle body adaptation with the vag. Denso iridiums (which I also us in my B6 and Touareg). No codes or lights other than o2 sensor

Try replacing the Denso Iridiums with a standard plug. Those caused all kinds of problems in the 1.8T when they first came out. I know first hand.

sparkster · 06-18-2012, 07:09 PM

Quote:

Originally Posted by Spinnetti

1999 B5 1.8tqm 260k mi

Wasn't running great, with a full load stumble. Replaced plugs and coil packs, and stumble went away. I can floor it in 5th at 20 mph and it just pulls gently away. Anything less than WOT it hesitates. What could cause that? I replaced the MAF (twice) and the Throttle body is new too. I ran injector cleaner though thinking leaky injector, but it had no impact. I have a test pipe and fresh turbo too. After this many miles, should I replace the injectors? Is it a waste to have them cleaned? (Any DYI?)

thanks.

I would plug the VAGCOM in amonitor what is is doing when it stumbles. could be a bunch of things.. First thing that comes to mind is the ICM/POS since you replaced a bunch of things already

05-10-2012, 04:21 PM	#2
4Driver4 Tech Guru Garage is empty, add now Join Date: Oct 2002 Posts: 32,388	Did you do a throttle body adaptation with the new throttle body? That would be step one. __________________ 4Driver4 Growing old is mandatory; growing up is optional. 2005 A6 Sedan Q 3.2 (wife's whip) 2000 A4 Avant Q 2.8 (daily driver) 1980 VW Scirocco (mid-life crisis car) 1983 Mazda RX-7 (revolutionary sports car) 2003 Mini Cooper S (just because) 1995 Mazda Miata, Superdupercharged(anti-Audi) 1999 Mazda Miata SSB (track beotch, no plate) 2003 GMC Yukon Denali XL (the anti-earth) 2004 Dodge Dakota (hey, at least it's stick and 4x4)

05-10-2012, 05:52 PM	#3
Prospeeder AudiWorld Senior Member Garage is empty, add now Join Date: Aug 2011 Posts: 862	Temp sensor will cause alot of problems. Did you use NGK or Bosch plugs? no Air leaks or boost leaks? Codes? EPC light? __________________ 1992 Audi 100 CS Quattro 1991 Audi 200 Turbo 1999 Audi A6 Avant 1998 Audi A4 quattro

05-22-2012, 09:49 AM	#7
RallyVermont Mr. McFeely Garage is empty, add now Join Date: Feb 2003 Posts: 17,483	Check your "L" hose from the back of the intake manifold.. this is known to leak and cause mystery boost issues, throttle hesitation etc... also if disconnected you'll lose your brakes. FYI - take a peek. __________________

05-27-2012, 05:01 AM	#8
Spinnetti AudiWorld Super User 1999 Audi A4 My Garage Join Date: Nov 2002 Location: Northern Kentucky Posts: 2,183	Vac hoses all look good. Coolant temp sensor didn't do it, but it was like $6, so why not right? Still have the part throttle stumble. Full throttle is fine, just part. Maybe I'll try adaptation again. One other thing it does, when you abruptly let off the gas under boost, it doesn't just bypass "cleanly".. diverter valve? is fluttering.. I presume the waste gate can't flutter, but it sounds funny. not sure how to describe it. I have a B6 too, and it doesn't do that. __________________ 2002A4 1.8TQMSPX w/o sunroof and a bunch of (functional) mods...

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