Nightmare of an evening:
I cannot get to the throttle body because the location on the 2L engine is inside a load of sheet metalwork. I got the rear plate off but even that wasn't adequate to detach any hoses. if i had a well lit garage, several hours, a Haynes manual & was willing to I'll all the metalwork, handbrake, etc. apart it could be possible but no chance on the street with a few hours of light to work by.
Vacuum hoses looked fine and I sprayed all over with carb cleaner with zero results so doubt there are any cracks or splits etc.
I took it on a blast to try and work some of the redex through. All I achieved was the bongo almost dying on 2 minor hills because the revs wouldn't go up (going too slow when i started going up them). It just started to stink of burning oil (or a slipping belt?) on a steeper hill whilst it sat almost stationary.
As soon as it was back on the level she would shoot off like nothing was wrong. This is the first time I've seen such problems on a hill so things are getting worse - usually hills aren't lightning fast but they've never been a problem. I also found that if i turn the AC on, the acceleration cannot pick up when moving for stationary - it stays crawling along. Turn the AC off and it starts to pick up speed. This all only applies to an rpm below 1500 or so - once I'm over that, hills and AC are no issue. The bongo just doesn't want to go from 500-1500rpm, especially if there's any sort of incline involved. Even got beeped taking ages to pull away from lights where there was a 5-10° incline
Checked brake discs, warm but not sizzling hot after i got back. Can't adjust throttle cable any further than it already is (not that it makes any difference, as the revs drop to 500 again as soon as it goes into gear - do the revs always drop when it goes into gear? I don't recall the revs dropping originally)
There's a healthy level of pressure coming from the tailpipe (hand test)
Next steps are to fire a load of carb cleaner up at the throttle body from as close as i can get after the airbox + change the spark plugs.
Any thoughts would be appreciated - it's such a distinct set of stuff that there can only be a couple of causes for it to appear all of a sudden.
I did change the oil 2 weeks ago but can't see any connection there...