There are similar threads on here but couldn’t find anything relating to my specific problem. The van idles perfectly on ignition when engine is cold but after a few minutes it starts to idle really fast and stays at a consistent speed. Sometimes if I blip the throttle it’ll bring it down to regular idling speed again but quickly returns to the high speed idle. To me that sounds like a throttle cable issue? Or potentially the auto choke? It’s a pierburg carb. Any advice as to how I go about fixing it would be much appreciated!
Thanks,
Aaron
1.9l petrol fast idle
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Aaronrichie
- Registered user
- Posts: 27
- Joined: 16 May 2022, 16:54
- 80-90 Mem No: 17490
- Location: Islandmagee, Northern Ireland
Re: 1.9l petrol fast idle
Undo the nuts on the "pancake" on top of the carb and move that to one side to get a good view of the choke mechanism to make sure it's not gummed up and is coming off as expected when the engine is warm.
An air leak making the mix slightly lean could increase the revs? Air leaks seem to be the cause of most of these idle speed issues. Check all round everywhere for deteriorated vacuum tubes, from the carb to the air filter box and the distributor vacuum advance unit, and the two tubes on the carb that connect the pull down units. Check for air leaks around where the brake servo vacuum hose attaches to the left side of the manifold.
The diaphragms in the vacuum advance unit on the side of the distributor and the choke pull down unit on the carb can also fail creating an air leak. The distributor advance is a easy one to check, if the revs change when you pull off the tube to it then it's probably OK. Pop a length of tube on the carb choke pull down unit and give it a good suck to see if it will hold vacuum, if you can keep sucking, the diaphragm is probably split and letting in air.
An air leak making the mix slightly lean could increase the revs? Air leaks seem to be the cause of most of these idle speed issues. Check all round everywhere for deteriorated vacuum tubes, from the carb to the air filter box and the distributor vacuum advance unit, and the two tubes on the carb that connect the pull down units. Check for air leaks around where the brake servo vacuum hose attaches to the left side of the manifold.
The diaphragms in the vacuum advance unit on the side of the distributor and the choke pull down unit on the carb can also fail creating an air leak. The distributor advance is a easy one to check, if the revs change when you pull off the tube to it then it's probably OK. Pop a length of tube on the carb choke pull down unit and give it a good suck to see if it will hold vacuum, if you can keep sucking, the diaphragm is probably split and letting in air.
1984 1.9DG wbx Autohomes rigid pop top
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Aaronrichie
- Registered user
- Posts: 27
- Joined: 16 May 2022, 16:54
- 80-90 Mem No: 17490
- Location: Islandmagee, Northern Ireland
Re: 1.9l petrol fast idle
Thanks for your reply. I have since discovered the problem is that sometimes the throttle does not return to where it’s touching the idle screw. Does this mean the spring needs replaced? Or perhaps it’s just positioned incorrectly as it wasn’t that long ago when I had the carb off for a thorough clean. Any tips as to how I do about fixing this would be much appreciated as I have MOT in 3 days!!