AAZ, RPMs out of control, doesn't seem like runaway though

[stubbornfarmer]

Hi All!

 Another weekend under the van (joy)

 So, on a long run down the motorway slowing for traffic. noticed revs were stuck around 3000rpm, on the hard shoulder checked obvious things like cables and throttle stops but to no avail, when re started each time it would return to the same RPMs that were just verging on being terrifying. (doesn't seem like runaway, turns off with the key and isnt killing itself with rpm)

 Checked breather and hoses but nothing unusual, tried running with breather disconnected but no change, oil level fine too. after 20 mins and no change in desperation i wound out the fuel screw a couple of turns just to see if i could limp it the last few miles home. this made things more confusing ultimatley: 2 turns out and wouldnt start anymore 1.5 turns back in and seemed normal again as if it never happened.

 Got home relieved, just taking it easy. went out to test it today and revs were normal when started, little underpower cos of the half tun on the fuel screw but no so bad. As it warmed I noticed it began to 'hang on' to revs between gears. hitting the pedal makes it rev up fast then climb down slowly even though the lever action is normal. 20 minutes later and its idling at about 2000rpm and really hanging onto the revs. Wish i could say it was the cables but it aint! 

 For background info, when i first got her she 'ran away' a few times after steep climbs or coming off the motorway, shortly after that she ate her turbo. Since replacing it there has been no runaway until this happened but the characteristics are different, originally you really bloody new about it for the 5 seconds of warp speed run away. this seems more like a sticky throttle, only it aint stuck!


any input valued as ever, cheers!
 

[kingler5]

Maybe check for oil inside the turbo, and/or the hose from the turbo to the intake manifold.

Really though, since it's constant, it could be an accelerator issue. Try disconnecting the pedal cable, and turning the lever by hand, see if you feel any inconsistencies.

While its holding those revs, can you go back and look on the pump and see if the accelerator lever is fully against the idle stop screw?

Do the springs around the accelerator shaft look normal?

Did you, or the previous owner open up the pump for any reason? Governor mod?

Have you messed with your cold start cable?

How about the boost pressure compensator? You could try disconnecting that line as well.


Just make sure you eliminate these possibilities one by one so you can find out exactly what the deal is.

[burn_your_money]

Has the residual fuel screw changed it's position? It's the one that the throttle rests against at idle.

[vanbcguy]

On my car the locknut had come loose on the residual fuel screw (the accelerator lever stop at idle) - it was doing EXACTLY that, it'd end up screwing itself in a bit while driving then hang at whatever speed.  Drive some more and it'd loosen itself again, drop the speed back down to 'normal'.  Went through a few very confusing cycles of that before I figured it out.