After my Disco 1 being parked up for a week, the cruise control now doesn't work too well.

It does work, but can't seem to get the accelerator pedal further than half way down.

Also, when I set it to a certain speed it kinda looses speed at first and then struggles to regain it.

If it's trying to accelerate itself back up to speed and struggling, I can see that the accelerator is only partially down and it's maintaining constant speed. If I tap the accelerator pedal down further it is then able to keep it there by itself until it's up to speed, at which point it releases the accelerator slightly, of course, but then cannot take it back down to accelerate when it gets to a hill, for example.

What do you guys think is wrong with it? It functions as it should, it just seems to struggle to move the accelerator pedal, but it doesn't seem stiff when used with my foot and it has worked flawlessly for 2 years until I left it standing for the last 8 days or so.

A leak in the vacuum hose joints is aways number one to look for. Number two is a faulty throttle diaphram.

Well I already kinda "pushed in" the throttle diaphragm with the engine not running and it slowly pushed in as far as it should and when I let go, you could see that the spring was trying to push it back out again but the vacuum pressure was slowing it down.

From being fully pushed in (by hand) to being fully "out" again, it took around 1 second.

The diaphargm doesn't look split in any way, but should it let air in and out with the engine not running like this?

Also, if there was a split in the hose, for example, would my brakes not feel squashy too due to the hose going off to the brake cylinder?

I'm sure you have a copy of RAVE, in it you will find the method of testing CC. both mechanical anf electrical.

I do have Rave, and all I can find in it is the road test which shows whether it works correctly or not. I have already done the road test and know what works and what doesn't - it still doesn't tell me whether the pump is gone, vacuum hose is perished, etc, etc...

It functions perfectly except for the fact that it "struggles" to pull the accelerator pedal down and then eventually "gives up" (like it does when it cannot maintain speed for a certain length of time, up a steep hill, for example). I have put some 3-in-1 oil into the cables in case that frees them up a bit, but that hasn't helped at all.

With the engine off, if I push in the diaphragm as far as it can go (to push all the air out of it) and let go of it, it returns back to normal within 1 second. Is that because I have compressed the air inside the vacuum hose, or because there's a leak? I guess there's no way to know.

So... step 1... replace all the vacuum hose??

The only time i've had any problems is with the vacuum hose ends splitting in the engine bay and pump area, so I now have now trimed the hose ends and wrapped tightly a few laps of pvc electrical tape around the ends of the hose before refitting, no more problems for the last three years.

So yes no. 1 is repair or replace the pipe. 2. the brake switch or throttal actuator

Right... it's fixed!

I had checked the ends of the hoses and they looked fine. However, I cut the ends off anyway, and pushed them back on. I cut off all three ends on the T-piece and the end on the vacuum pump/solenoid. Went out for a test-drive and it works perfectly

Next time, though, I will need new hoses as these are as short as I'd ever want them now!

Thanks for the help!!

Fishsponge,
when you need to change the hose just use reinforced fuel hose of the correct size.
relatively cheap and lasts forever.

cheers

Jim A
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1996 300Tdi auto(Jap reimport)

good idea - thanks for that!