forum.audiv8.com Foren English Audi V8 Forum Engine won't hold 1600rpm

Odd one here. (Not me; the problem)*

Audi V8.
The car has developed an inability to hold 1600rpm. Which is quite irritating as this is close to gentle town driving. It Revs up to 1500+ Normally, but when it gets to 1600, it oscillates up and down by about 150rpm. Down, up, down, up, down, up (it's kind of repeatable)
It does this in park, neutral, or 1,2,3,D, and R. The effect in gear being like a loss of fuel supply.
Any slight increase in throttle pedal pressure simply results in a more aggressive loss of power.

Give it a boot from idle to above this, and all is fine. It revs through to the redline off load, and easily through to normal levels in Econ, Sport, and Manual modes.

It idles fine. Rock solid.

I'm making another cable to pull the codes (note to self- stop leaving cables behind when you move home), but in the interim, are there any similar events in other Motronic based systems?









*granted, it might be me! too.

I guess fault reading is required. Did this cr... appear in coherence with the viscous clutch renewal or other attempts to engage the auxiliary fan?

The car had been running fine after swapping the viscous fan.

I pulled the codes whiich have come up with 2121, throttle switch. I tested it off the car, after cleaning the contacts (some moisture around pins 5 & 6, with verdigris). It appeared to give a good open closed, 0ohm to open circuit result using a decent DVM

Well, it was a good excuse to build a new test lead. A nice tidy one with a box, and everything. Which was also a good excuse to run all of the diagnostics.

1. I need to run the diagnostics again tomorrow, as there may be an erroneous fault. I had disconnected the switch during the day, and run the engine to see what happens.

2. The relays for the cooling fan are being switched by the diagnostic output test, so the problem is the poer itself. So that's a bonus.

3. My climate control compressor relay is not being switched, so that's another fault part diagnosed.

What is the difference between the -B and -D versions of the throttle switch?

Fixed!

Or, more accurately, not happening anymore.
I took the car for a test drive this morning, and conspired to drive in the problem rev range. Not a sign of trouble.