Revving itself at tickover! What's going on?

Pipsqueek · Post by **Pipsqueek** » Tue Oct 30, 2007 10:39 pm

Help me pleeeeease

Recently bought the big black bongo bus

and all going well until... just sitting there minding my own and the revs are climbing and dropping with no throttle at all, just like i was blipping the throttle

. Now i'm not not even close to blond and have realised that 'automatic' doesn't include throttle, so has anyone got any ideas (something nice and cheap to put right would do nicely!) Oh halloween! perhaps its haunted

Any sensible ideas would be most gratefully appreciated cos i can do silly all on my own

over to you...

francophile1947 · Post by **francophile1947** » Tue Oct 30, 2007 10:43 pm

Diesel or petrol engine?
I don't know the answer but it will help others if they know what engine it is.

Pipsqueek · Post by **Pipsqueek** » Tue Oct 30, 2007 10:52 pm

Good point, well made! Oops

Diesel 2.5

francophile1947 · Post by **francophile1947** » Tue Oct 30, 2007 11:02 pm

Are the revs going higher than normal tickover, or just varying between tickover and slower?
Does it run OK when accelerating, or is it down on power?

Post by **Ian** » Tue Oct 30, 2007 11:06 pm

It's been reported before. It is a faulty throttle position sensor.

corblimey · Post by **corblimey** » Wed Oct 31, 2007 1:00 am

Is it an auto or a manual?

Is it revving when the vehicle is stationary, in neutral and your foot is not on the pedal?

If so, it seems unlikey it's the TPS since that only reports the throttle position back to the ecu. If, on the other hand, the revs are fluctuating whilst driving at a steady speed (i.e your throttle position is not changing) and you're driving an auto then you may find the revs fluctuating (as the gearbox hunts) with a TPS fault.

I'm no expert though so don't take this as gospel.

Either way it's easy enough to check if you have a multimeter.

Look at the last post on the this thread page where I've explained how to do it.
http://www.igmaynard.co.uk/bongo/forum/ ... hp?t=14174

HTH

jimsmimm · Post by **jimsmimm** » Wed Oct 31, 2007 10:34 am

you dont have your aircon switched on by any chance....

Ralph · Post by **Ralph** » Wed Oct 31, 2007 1:09 pm

Has it got the switch NR drivers right knee with a pretty pic of a engine ?
if on switch off as that fixed it ? if so don't bugger about with it again.
No, look under drivers seat on the fuel pump NR the bottom you will see
a arm this controls the fast idle is it moving in time with the revs?
"no" then you may have a air leak down NR the rear of the engine but
fixed to the body of the Bongo you will see a unit "the fuel filter", it may
be loose look for leaks in the pipes loose unions.
If the arm is moving it could just be that it needs adjusting, if the fast
idle is set to high the ecu thinks you are revving the engine and turns
off the fast idle the revs then slow the ecu thinks you have stopped
and switches it back on again so you get the fast slow rev thing but
because of how it works you have to balance the fast idle for a cold
engine and fast idle for when you switch on the air con.
If it stops the fast slow thing when the engine is fully warmed up it
must be something to do with this system or as someone said
the throttle position sensor.
If you look at the top of the engine in the middle driver side just above
the fuel pump you will see 2 small vacuum valves the one nearer the
back with the black electrical plug if you carefully unplug it, it as
a clip to keep it in, that should cure it but the down side is that you wont
get fast idle on cold start.
Hope this drivel helps

Pipsqueek · Post by **Pipsqueek** » Wed Oct 31, 2007 3:03 pm

Wow, thanks !
In answer to a few questions -
Yes, an auto.
Yes, it blips above normal tickover.
Yes, does it in park (not sure about neutral) when stationery and in drive.
Runs fine apart from this revving, no power loss detected.
Not noticable when moving.
Aircon not on.
Whats a scavenge fan ?

Can't hear fan running if that helps

What is that switch by my right knee with the pic of the engine that i've been b...ing about with, can't find it in the handbook?? (It is off by the way) I won't touch it again, but when a mystery button is found it has to be pressed doesnt it??

I dont have a multimeter but know a man who has

so hopefully we can begin the trail of the TPS fault or air leak

Thanks on all your thoughts

Ralph · Post by **Ralph** » Wed Oct 31, 2007 3:31 pm

The switch is used in very cold weather much colder than here,
it closes a valve in the exhaust system and increase tick over speed
but if your Bongo as had a new exhaust it most likely wont have the
valve and pressing the switch will speed up the tick over to a point
were you get the fast slow rev thing,
I suspect but am only guessing that the cooler weather is tripping
the higher cold weather start and that is why it's hunting, I think
that pulling the plug in my last post will cure it as mine as that valve
broken and runs ok without it you may not notice a thing.
When you turn the air con on does the tick over go up ? by a lot
or not at all ? The scavenge fan is under the engine cover to the
front the idea being as the engine is more or less in the cab
with you it come on if the area round the engine gets hot and cools
the air so it doesn't cook you or the engine.
Ps buggering about is a technical term

smartmonkey · Post by **smartmonkey** » Thu Nov 01, 2007 12:51 pm

Dont worry too much about air leaks. The engine is not restricted for air intake so a leak makes no difference to idle.

Ralph · Post by **Ralph** » Thu Nov 01, 2007 7:30 pm

Air leaks in the manifold don't matter much but in the fuel
lines and filter they can cause all sorts of strange happenings.