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· Registered
1,186 Posts
Discussion Starter · #1 · (Edited)
We've got a 2000 Beetle 1.8T that won't quite rev to 2000 when cold , or 3000 when warm. These limits are consistent, with very little power. This thread is for good old trouble-shooting without the help of scans. We can't scan it for unknown reason(s), but never could scan this car.

-The car ran great last winter, and was running well when parked in March. It probably has a tune of unknown origin. The check engine light was always on.
-It sat outdoors for 8 months, and then intermittently started acting up (not revving over 2K when cold or 3K when warm), but finally worked well in Nov/Dec after cycling the ignition a few times.
-Then after sitting until Jan, cycling the ignition no longer helped anymore.

-Replaced battery with a brand new one.
-Car starts on a dime and generally idles acceptably when cold (very slightly rough, but with 2K rpm max at WOT), and fully smooths out once warm (but with 3K rpm max at WOT). These rpm limits were consistent after many tries.
-Warm or cold, it's way down on both rpms and power (slowed to under 20 mph up hills on the test drive).
-A vacuum gauge (actually the low resolution negative section of a combo boost/vac guage) reads steady negative teens range at idle, but unsure of units (psi or in-Hg, etc).
-Tried cleaning the MAF (especially since it's behind a cheapo aftermarket cone filter), but no difference. Disconnecting the MAF completely was also no better.
-Cleaned out light gray crank sensor connector with brake clean and compressed air in case of moisture ingress (potentially from melting snow), and water-proofed with dielectric grease, but again no difference.

So far our to-try-next list includes checking ECU grounds, and replacing coolant sensor, but time's running out.

Assuming it's not practical to extract codes (working on that separately but doesn't look promising), any idea what might be causing this particular loss of revs and power?

· Registered
137 Posts
How old and what plugs are in it?

Vacuum lines, this car doesn't sound like it's a main concern for consistent maintenance, so there are check valves, lines and the like that age...wear and when left to sit, they die. T
The car is 23 years old.
Coolant temp sensor in the flange on the head, how old is it and what color?
Crank position sensor?
FPR condition?
O2 sensor age and condition?
How old is the fuel? Has the fuel filter ever been replaced?
How is the catalyst?

Fuel pressure?(before and after the rail)
Have you logged the afr after full warm up( a few miles of driving at temp)?
Any codes at all?

· Registered
1,186 Posts
Discussion Starter · #6 ·

It's a low-budget street-legal ice racer that basically gets attention once a year (usually just before the Jan-Mar ice racing season). The car got new stock plugs, coolant sensor (green one at the head), MAF and silicone vacuum lines about 13 months ago. It ran strong and reliably last season.

It randomly started once more from cold without the low rev cap this weekend, so we took the opportunity to get it out of the snow and moved indoors. No boost after the first rev so I guess that's its limp mode. But the next morning it was back to the same nearly undrivable low revs limit.

Some of the plastic coolant flanges are weeping. We ordered metal replacements for a Golf, which just arrived, but unfortunately the ones we needed aren't the right configuration for a Beetle.

We'll add all your other suggestions to the growing list, thanks! Except for the scanning which simply isn't working for unknown reasons (which itself is back on our list).

· Registered
1,186 Posts
Discussion Starter · #9 ·
Yes! Apparently my cable can no longer scan K, but still works on CAN. Borrowed cable only works on K. Tons of low voltage codes etc. Cleared all. Only throttle body and secondary o2 heater came back. Calibrated TB, started car in garage and rescanned - only secondary o2. Test drove to store and back. No boost on the way to store, but boost worked intermittently on the way back. Will rescan soon. I wouldn't have thought secondary o2 heater would cause limp mode (assuming that's the reason for no boost). More later.

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1999 Golf GTI 2.slow, 2000 Beetle GLS 2.slower, 2001 Golf GTI 1.8t
1,368 Posts
I dont think the secondary O2 is your issue either, but if you still have it and it's shorting, it could cause a low voltage supply issue for other sensors on the same fuse.

Maybe unplug it at the connector box under the car in the meanwhile?

· Registered
1,186 Posts
Discussion Starter · #11 · (Edited)
Thanks, I'll try that soon. In the meantime, here's the Beetle engine scan from just AFTER the TB adaptation and test drive (note that the TB code 17967/P1559, which was the reason I'd done the TB adaptation, has returned, along with additional TB-related codes):

Address 01: Engine Labels: 06A-906-032-AVC.lbl
Part No: 06A 906 032 C
Component: 1.8l 5VT NB HS G 3077
Coding: 00001
Shop #: WSC 00066
VCID: 1E3983BA9AB7DC7FD8-5178
7 Faults Found:
17526 - Oxygen (Lambda) Sensor Heating; B1 S2
P1118 - 35-00 - Open Circuit
17606 - Oxygen (Lambda) Sensor Heater Circuit: B1 S2
P1198 - 35-00 - Electrical Malfunction
17950 - Angle Sensor 1 for Throttle Actuator (G187)
P1542 - 35-00 - Implausible Signal
17579 - Angle Sensor 2 for Throttle Actuator (G188) Implausible Signal
P1171 - 35-00 -
16524 - Oxygen (Lambda) Sensor B1 S2
P0140 - 35-00 - No Activity
17967 - Throttle Body (J338)
P1559 - 35-00 - Fault in basic settings
17973 - Throttle Actuator (J338)
P1565 - 35-00 - Lower Stop not Reached
Readiness: 0010 1101
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