John535is

My son recently purchased a 1.8T quattro. It had a few issues so I replaced the water pump, timing belt, tensioners etc, accessory belt & tensioners, PCV, valve cover gasket & chain tensioner gasket, engine mounts, plugs and coils, filters etc.

Engine runs nice now with no leaks but I noticed when changing gear the engine does not back off revs much, just a slow decrease. Is this normal for the 1.8T engine or is something inhibiting the engine revs from coming down? If it was 20 years ago I would say the spring on the accelerator cable or the carby needs replacing to shut the butterfly, but that was when things were simpler.

Any ideas?

lyleswk

My does the same. It seems to hold the RPMs for about 2 potatoes after the clutch is depressed and then drops to idle.

aTOMic

When I first got my '98 Passat with 1.8T 5M (purchased new), I thought the same thing, and drove others on the lot... as they say "They all do that". I assume it helps keep boost up; but it does it even when off boost. Maybe it's got a really heavy flywheel .

I added a GIAC chip about 100k miles ago; best $600 I ever spent. I think that reduced the after-lag somewhat. I went from 8 PSI boost to 22. Drives like a different car, still gets 35MPG. Worst tankful I ever got (all city, all rapid accel) was around 20MPG.

-Tom

A4Audi4Fun

Check if cruise control works. Hanging revs when changing gears is a symptom of clutch switch failure; cruise control can confirm this; have had this happen to me.

lyleswk

Just FYI, my cruise works okay...

aTOMic

How long do the revs "hang"? We're talking about just a second or two tops.

Once I had cruise on and exited the highway and put it in neutral (5-speed) and the revs went through the roof! Derp moment on my part. I can't remember if I slid it out of 5th (in which case one would expect it to try to accelerate and the revs going up) or if I declutched.

Can't test it now as I have the common ABS module failure. VW should be liable for a recall, I don't care if the car has a million miles on it. Just my opinion.

-Tom

A4Audi4Fun

@aTOMic, In my case it wasn't more than a second; just found it weird when lifting off throttle and pushing the clutch in, to have the revs stay up. That clutch switch is supposed to prevent that over rev condition when in cruise mode, amongst other things. VCDS scan should show an error - this is the error code that I got

1 Fault Found:
001796 - Clutch Switch (F36): Implausible Signal
P0704 - 004 - No Signal/Communication
Freeze Frame:
Fault Status: 01100100
Fault Priority: 2
Fault Frequency: 1
Mileage: 38800 km
Time Indication: 0
Freeze Frame:
RPM: 1812 /min
Load: 22.7 %
Speed: 26.0 km/h
Temperature: 88.0°C
Temperature: 23.0°C
Absolute Pres.: 990.0 mbar
Voltage: 13.970 V

More detailed discussion here
http://www.audizine.com/forum/showth...and-revs-go-up

John535is

Thanks for the replies. Tested the cruise control and you are correct, that's not working properly so I will change the clutch switch and report back.

John535is

Thanks A4Audi4Fun, replaced the clutch switch as recommended, revs drop during gear changes now and cruise control now working. Thanks for the advice.