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Discussion Starter · #1 ·
For a number of months, I've been dealing with an issue on my 2000 1.8t that's causing my throttle to only open to about 20-25% (reported by the ECU), and this randomly shows up and goes away to work normally. It's happened in the middle of acceleration, as well as in the few minutes the car is off to go into a store or overnight, and then will continue to act the same for multiple days, then will switch back. The car otherwise runs just fine. The car is running with a modified tune, however I've also tested it with a stock ECU and have the same issue. I've got a downpipe using just the front O2 sensor (new sensor), as well as an aftermarket air filter. SAI pump and associated equipment has been removed, but the PCV system is still in place. All the vacuum tubing has been replaced with silicone tubing and pressure/smoke testing has shown no leaks. I've tested with the MAF plugged in and unplugged and didn't see any difference. Diverter valve, throttle body, and throttle pedal unit have all been tested with working alternates and showed no changes. This could be some sort of limp mode, but I'm not getting any sort of codes to indicate that. I'm thinking there must be some sort of electrical issue, as VCDS will not recognize the engine module. There's also a noise that comes from the throttle body when the key is on but the engine is off - it kind of sounds like it's trying to recalibrate or there is pressure on the throttle plate, however this has all been cleaned. O2 readings are also not being recognized correctly by the ECU. All fuses have been checked and I've checked most of the relays, but I haven't found any issues so far. I'm not really sure where else to start looking for electrical issues, so any input is greatly appreciated!
 

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Chassis Type: 1C - VW New Beetle (1998 > 2010)
Scan: 01 02 03 08 15 17 19 25 29 35 37 39 46 54 56 65 75

Mileage: 205080km-127430miles
-------------------------------------------------------------------------------
Address 01: Engine Labels:
VCID: 55F7887BDC0ECA43A47-5160
Note: Excessive Comm Errors


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Address 03: ABS Brakes Labels: 1J0-907-37x-ABS.clb
Part No: 1J0 907 379 AF
Component: ASR 20 IE CAN 0001
Coding: 13204
Shop #: WSC 00066
VCID: 75B7E8FB3CDEAA43847-4B1E

No fault code found.

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Address 15: Airbags Labels: 6Q0-909-605-VW5.lbl
Part No: 6Q0 909 605 A
Component: 06 AIRBAG VW5 0004
Coding: 12342
Shop #: WSC 00066
VCID: 353728FB7C5EEA43447-4B3C

2 Faults Found:
00532 - Supply Voltage B+
07-10 - Signal too Low - Intermittent
01217 - Side Airbag Igniter; Driver Side (N199)
32-10 - Resistance Too High - Intermittent

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Address 17: Instruments Labels: 1C0-920-xx0.lbl
Part No: 1C0 920 901 F
Component: KOMBI+WEGFAHRS. M73 V07
Coding: 07202
Shop #: WSC 24154
VCID: 1F1BEA53EEA24013BEB-4B1E

Subsystem 1 - Part No: Ident
Component: Nr. Wegfahrs.:VWZ5Z0Y2036101
Ident.-Nr. Wegfahrs.:VWZ5Z0Y2036101

2 Faults Found:
01314 - Engine Control Module
49-10 - No Communications - Intermittent
01316 - ABS Control Module
49-10 - No Communications - Intermittent

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Address 19: CAN Gateway Labels: 6N0-909-901-19.clb
Part No: 6N0 909 901
Component: Gateway K<->CAN V072
Coding: 00006
Shop #: WSC 00066
VCID: 70B9D9EF43BC8F6B571-4B1E

2 Faults Found:
01314 - Engine Control Module
49-10 - No Communications - Intermittent
01316 - ABS Control Module
49-10 - No Communications - Intermittent

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Address 46: Central Conv. Labels: 1J0-959-799.lbl
Part No: 1J0 959 799 AJ
Component: 5X Zentral-SG Komf. 0001
Coding: 00256
Shop #: WSC 04938
VCID: 06559F375138B1DB9DD-4B1E

Subsystem 1 - Part No: 1J2959802C
Component: 5X Tõrsteuerger. FS0002r

Subsystem 2 - Part No: 1J2959801D
Component: 5X Tõrsteuerger. BF0002r

3 Faults Found:
00953 - Interior Light Time limit
25-10 - Unknown Switch Condition - Intermittent
00943 - Heated Exterior Mirror; Driver Side (Z4)
35-00 - -
00944 - Heated Exterior Mirror; Passenger Side (Z5)
35-00 - -

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Address 54: Rear Spoiler Labels: 1C0-959-733.lbl
Part No: 1C0 959 733 B
Component: Heckspoiler 0002
VCID: 2A0D0B87A5E0B5BBD95-51A8

No fault code found.

End----------(Elapsed Time: 04:15, VBatt start/end: 14.1V/13.9V)-----------
 

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So, you have quite a few codes and a code for low voltage! From what I have experienced, you can get quite a few trouble codes; from a low battery or charging issue. If you have been removing and replacing parts; while, forgetting to remove the battery terminals, you will get related parts codes as well.

So, codes, will build up over time or when, testing, removing and replacing parts, while concentrating on live data testing, etc.

So, it can be a good idea; to clear codes and see what comes back.

Intermittent, issues, can be a real challenge to find and get to happen, when you have a scan tool, hooked up or viewing live data, etc.

The fact that you have a modified tune and ecu; typically, can open up another aspect of possible variables. From what you are saying, swapping in, a "stock, known good" ecu; has not made any difference, at all?

A bit of history of the vehicle; then, when this issue started cropping up, could be helpful for us, as well.
 

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Now, on to some resources; that might help, here is a YouTube video by "coolairvw", a VW specialist in Kansas City, that runs his shop or KanasascityTDI.com

He has some good info and testing; he does with live data, reader block in VCDS:

This is on a Jetta 1.8T with a similar issue and his issue, was a bad ecu from shorted out 02 sensors or messed up programming, etc, etc. This VW shows all the worst Mark IV VW "mods" one finds on these cars, these days and beat to " ", Ugh!

Jetta 1.8T no throttle response - Bing video
 

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So, you might want to review the video and the discussion; check related issues and report back, if you think, there might be some helpful info that relates to your current issues. Thanks.
 

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Discussion Starter · #11 ·
Thank you for all of the info! I'll take a look through this and see if I can find anything. I have already done quite a bit of troubleshooting and haven't found any clear cause. I typically hook up the car to a battery tender when doing scans, and still see intermittent connection errors. I do have a stock ECU that I've swapped in, and the same issues are still present. The issue first popped up while I was accelerating one day, and I heard the wastegate open and all of a sudden I had very little power. The engine appears to run and idle fine when this is going on, but the ECU reports the throttle only opening to about 20%, so boost is quite limited as well.
 

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I think the possible wiring harness, plug issues; should be considered, to the 02 sensors, ecu and throttle body.

VCDS can show bus status along with other live data component reader blocks; when viewing those in real time and the car is running, you can try the “wiggle test”, to see if the live data, drops out or acts strangely. That could indicate a connection problem or grounding out of that part of the wiring or part it is connected to. That could help, narrow down the problem and help do a process of elimination.

A visual inspection of the grounds under the battery for corrosion; has been a historical problem, clean if needed.

Inspect plugs, terminals for green corrosion and bent pins for ecu, etc; signs of water ingress in the dashboard, plenum, from clogged water drains, has also been a common issue to be aware of as well.

Deoxit and CRC QD cleaner has been good for these corrosion issues, dirty connection problems and post cleaning; some dialectic grease, to seal things, protect terminal connectors for the future, is something to try.

Deoxit:


CRC QD cleaner:


Dialectic grease:



Report back anything you find and we can go from there.

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PS: i noticed you said; you have a performance, non stock, down pipe and are “only” using the front 02, sensor.

What is the situation with the b1s2 post cat 02 sensor? As shown on the coolairvw video; electrical problems with the 02 sensors, can cause all kinds of ecu, throttle drop out and drivability problems.


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Discussion Starter · #14 ·
Post cat O2 sensor is just disconnected right now - I do have the sensor but it is stuck very tightly in the old cat. The tuner had said only the pre cat sensor is necessary so I've just left the other one disconnected and haven't bothered to buy a replacement. The port in the downpipe is plugged with a bolt, but I do wonder if the lack of a sensor reading is causing some issues with the ECU now.

I was also able to get some very interesting info today that I had not previously seen - today when I started the car it was not accelerating correctly, however I got it to work normally by clearing DTCs via OBDII while driving. I was then driving around for awhile at low speeds and everything was working normally. I got on the highway and had no issues at any speeds for 10-15 minutes, then while on cruise control I went to step on the gas and again had very poor acceleration. I cleared DTCs again, had to step on the gas once with it still not working properly, then all of a sudden I had proper acceleration again. It was being very finicky though, and would stop working after just a few seconds if I would accelerate hard. I repeated this half a dozen times and every time I clear the codes all of the same ones come back up again as they're related to the removed O2 sensor and SAI pump (codes are P1432, P0140, P1118 and P1198). I'm not getting any EPC light or any other error codes, but it definitely seems like the ECU is going into a limp mode. I can hear the wastegate open when it stops working, though I'm not sure if that's the product of the ECU going into limp mode or if it's entering that mode after the wastegate opens.

I'm going to see if I can get the post cat O2 sensor off the old downpipe removed without destroying it to give that a shot. I've also been cleaning up all of the electrical connectors related to the O2/throttle system, as well the ECU. I know the water drains in the ECU compartment had been plugged up previously, so there's some corrosion on that side of the compartment, though everything on the ECU looks to be in pretty good shape.
 

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You have allot of codes, soecifcally related to the b1s2 02 sensor; which is the post cat 02 sensor. A visual check and electrical testing of the terminals as per the service manual would make sense and as shown in the “coolairvw” video, a damaged wiring harness, messed up plugs, terminals and 02 sensors; can cause damage to the ecu and cause the no throttle issue. In his case, the harness had been grounding out and even dragging on the ground or caught on road debris?

As noted before, we have also seen; where the plug and terminals ends to the valve body, have a intermittent connection, as the terminals are loose or damaged. Note the thread i linked above; while viewing live data you “wiggle” the harness and plug, to see if the signal drops out or acts erratic? If it dies a new pigtail could be replaced and this was a fix for him!

I’m pretty sure this is the right pigtail; confirm by comparing the vw part # on your current one:

New 6 Pin Throttle Body Pigtail Connector For Audi TT VW Beetle Jetta 1J0973713



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Discussion Starter · #20 ·
Finally got the secondary O2 sensor replaced with a new one. After some testing it seems the issue is less frequent, but it's still occurring. Only code now is P1432 because the SAI pump has been removed. Clearing the codes is still working to reset the ECU. I still find it surprising that no new codes show up when it goes into limp mode. I'm thinking you're correct and it's got to be related to a bad wiring harness or bad ground somewhere.
 
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