So, I bought Doink's old bus a few weeks ago... Never had a fuel injection bus before and I must say it's jolly nice! I hope it doesn't go wrong as I don't have a clue how to fix it!! Runs great, probably the nicest type 4 engine I've ever driven....however...When I lift my foot off the loud pedal the revs don't drop straight away, takes a couple of seconds and is gradually taking longer....if I slow the engine using the clutch its fine and stays at low revs...if I don't it just carries on running at higher revs for a while. I've checked for air leaks and vacuum leaks in the traditional manner (squirting wd40 on the joins etc...) and everything seems to be fine. I'm hoping it's something silly. Any advice appreciated!
It could simply be that as the air temperature drops, the lubrication on the throttle is getting stiffer. What happens if you operate the throttle from the engine bay ?
I know nothing about FI but somewhere in the system there is usually a return spring. A lot of engines have a long spring attached to the bodywork around the rear engine hatch. I'm not sure whether this is a factory fitment though. Anybody?
Check the distributor weights are working properly, ie no broken springs etc and they return as they should and are lightly oiled. Carefully inspect the S boot for cracks. That's really common as it sits in a stress position for decades. As @davidoft suggests, it may be an air leak you haven't found yet such as the one way valve to the servo. Welcome back Andy btw... Ooh, and that the egr hole has been properly blocked off if it's all been modified.
That could be worth a look mate! It's been gradually getting more noticeable as we've been all over the shop in the bus over the summer. Don't think it's a trapped cable as the revs would increase again when I dip the clutch....once it's been slowed down it stays there. Thanks for the welcome back! Motorhomes were fun, but you just don't get the feeling you get rattling around in a bay!
You could watch the timing with a timing light but it's a chicken or egg thing, is the timing keeping the revs up or the revs advancing the timing. lol Been there. Take the rotor arm off and add a few drops of oil onto the felt therin. This is the only lubrication the advance shaft gets and a lot of folk never do it. The weights themselves rarely seize and if a spring broke I don't think it would stay slowed down.
If you can get it to slow down by loading the engine, maybe it could be the other one that gets people. The idle speed is high because of e.g a vacuum leak or a setting error on the throttle body or carburettor throttle. The centrifugal advance starts to work, around 1000 rpm. (or it has stuck with some advance as @Zed suggests) Somebody assumes it is idling at the correct speed and sets the timing to 8 degrees BTDC, but some of that timing advance comes from the centrifugal advance (or a sticky distributor) If you slow the engine by loading it, the centrifugal advance vanishes, leaving you with effectively the static timing. So then the idle will slow right down - it might be the correct speed, its probably a bit slower than the typical 850-950 rpm. You would see that on a timing light. At the slowest engine speed the timing advance will be less than 8 degrees. To fix it you need to find out why its running fast and fix or adjust the speed down, then adjust the timing and iterate the two until it is both idling at the right speed, and the timing advance is sitting at 8 degrees BTDC.
Hi, I had what sounds like exactly the same problem with my 2L FI bus. RPM remained high after pressing the clutch, but could be slowed by releasing the clutch and slowing the vehicle down. The problem turn out to be a faulty deceleration valve - the flying saucer shaped thing attached to the fire wall. Since this was replaced, I haven’t had that problem again.
