Very High Idle - suspected waxstat

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DMReynolds
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Very High Idle - suspected waxstat

Post by DMReynolds » Sun Jan 14, 2018 10:51 am

Hey Folks - I’ve been digging around here trying to diagnose my fault:

Extremely high idle from cold start (3000+)

This lasts for 5-10 minutes (very embarrassing driving slowly through built up area, sounds like I have two lead feet...)

Once engine is warmed up it’s like driving a different car, instead of fighting to stop it getting away from me into a wall, I’m fighting to keep from stalling.

Coming off dual carriageway (85mph) to a side road (40mph) the hot engine tick over is juddery and wants to kick.

I suspect a wax stat and possibly a second problem, but don’t want to chuck £75 (!) at a new stat and be wrong!

Have considered a Weber, but (without wishing to open that old debate again) understand that mpg is generally better on the 2e2. Definitely don’t want to chuck £75 on the 2e2 if I then need to swap for a Weber.

If only the insurance bump wasn’t so high for a 2.0 16v swap...

Any ideas folks?



BlackGTX
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Re: Very High Idle - suspected waxstat

Post by BlackGTX » Sun Jan 14, 2018 12:03 pm

My 2l 16v conversion was +£60 on the insurance



DMReynolds
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Re: Very High Idle - suspected waxstat

Post by DMReynolds » Sun Jan 14, 2018 2:35 pm

I’m still waiting for the quote, but as I only passed my test 3 weeks ago I fear it may be horrendous...



DMReynolds
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Re: Very High Idle - suspected waxstat

Post by DMReynolds » Sun Jan 14, 2018 8:29 pm

Update:

I've had the stat off and bathed it in boiling water. The pin was all the way in, flush with the brass cylinder it protrudes from. A few minutes in boiling water had it out to around 5mm proud of the plastic housing (10mm from the brass cylinder).

I popped it back on the Pierburg but the problem remains, still idling at 3000 for 5-10m before dropping back to ~1000 :(

I did however find a stray lead hanging out around the carb. There is a set of three connectors routed together along the firewall under the green vacuum sphere. Two of these are connected to the driver's side of the carb (pictured / pointed out) but I have a third from the same group just hanging loose. Anyone have any idea what this is supposed to be attached to? I thought it was just a ground, but it has a male spade terminal and two wires.

Any help much appreciated!

(sorry about the pictures...)

Image

Image

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james butler
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Re: Very High Idle - suspected waxstat

Post by james butler » Sun Jan 14, 2018 9:03 pm

i had some wires fall out on mine and they were the reason the revs shot up to 3-4k revs
they went to a funny looking diphram solinoid thing on the drivers side of the carb.
you should be able to see it from the drivers side if it is that


I dont mind project cars but I HATE SANDING!!!

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james butler
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Re: Very High Idle - suspected waxstat

Post by james butler » Sun Jan 14, 2018 9:06 pm

the wire in your first picture i think goes to the preheater on the front of the carb somewhere this i seem to recall dasiy chains to the other solinoid thingy i mentioned earlier.
there should be another similer thicker red white wire that goes to the hedgehog element under the manifold too


I dont mind project cars but I HATE SANDING!!!

DMReynolds
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Re: Very High Idle - suspected waxstat

Post by DMReynolds » Mon Jan 15, 2018 3:07 pm

So it turns out that this little wire is supposed to go to the 'part throttle heater' on the carb. The female lead has come off mine in what is apparently a common problem.

Apparently, that wont be what's causing the high idle, so I'm back to square one...

Anybody got any experience with waxstats and how to confirm that they are knackered?



hiltow
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Re: Very High Idle - suspected waxstat

Post by hiltow » Sat Jan 20, 2018 2:47 pm

The connector you mention is NOT for the 'hedgehog' fuel preheater, but is likely to be part of the problem.

It serves the thermal time valve (TTV), which regulates hownthe carb operates during the warmup phase. The TTV is the small thick round black plastic piece at the top left rear of the carb. It also governs the operation of the throttle plate actuator, the gold metal disc with the piston coming out of it, located underneath. After the waxstat and the throttle plate actuator, the TTV is probably the main culprit.

Check that the TTV has current by applying a tester to the feed connector with the ignition switched on first. The TTV is difficult to test with out a vacuum pump and ohmmeter, plus ability to do so a 4c and then 15c temperatures. May be best to renew - typically £50 or so on eBay for a new one.

To test the throttle plate actuator, with the engine cold the pushrod should be fully extended to the cold start position. Start the engine and the pushrod should retract to the hot idle position i.e. move back from touching the throttle stop screw thread in front slightly, which his the cold start position. At fast idle, the position should be maintained according to the waxstat starter position. You may need an assistant for this test and the next one.

In a quiet area, have someone turn on the ignition only whilst you listed out for a faint 'click' sound from this part of the carb. If you can hear that then the e!ectric switchover valve (square metal block under the backnof the TTV) is working - this is a good sign.

I could write much more, which is why you really need to track down a copy of the green Haynes 'Solex and Pierburg Carburettor' manual - it contains all the info and sets out the tests in logical format after explaining how everything is supposed to work / relates to one another.

BTW, the waxstat test isntomalwayswhen apply 30N force to the top of the pin at a temp of 20c to the stat and measure the distance between the stat casing mating face and the top of the pin this should be 2mm. If not,vreplace the stat.

Finally, make sure that ALL you vacuum hoses are connected properly and aren't split or leaking. As I say, you really do need the dedicated Haynes manual I mentioned. The stat is fairly cheap to replace, so I'd do it anyway for P.o.M.

Don't give up!



DMReynolds
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Re: Very High Idle - suspected waxstat

Post by DMReynolds » Sat Jan 20, 2018 2:53 pm

You’re a hero - thanks - I’ll try this when I’m with the car next (it’s a project with a student, so only have weekday access).

Definitely get a click from the carb on power up tho He - so I guess the TTV is ok.

Wax stats seem to be about £70 - anyone know a cheaper supplier, seems a bit much when you can (occasionally) get a whole carb for that on eBay!



mark1gls
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Re: Very High Idle - suspected waxstat

Post by mark1gls » Sat Jan 20, 2018 3:31 pm

Glad someone has helped, I know nothing about the Pierburg carb, I repaired my carb once then gave up the 2nd time it went wrong as the car was my daily so I needed it fixed quickly, I went out and bought a new Webber carb as they are simple carbs to work with.
Fingers crossed you can find out what’s wrong with.


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hiltow
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Re: Very High Idle - suspected waxstat

Post by hiltow » Sat Jan 20, 2018 9:51 pm

GSF did have the plastic waxstat, which might be the cheapest?

These carbs are quite complicated, so complete disassembly is for the brave / experts / those who can concentrate. The thing to remember though is that the carb doesn't really wear out in itself. There's just a set of 4 or 5 individual components that dictates whether the carb a whole 'whole' works - the good news is that most can be replaced without reading open the whole unit. The problem's finding the weakest link:

TTV, waxstat, choke pulldown, throttle plate actuator and electric switchover unit.

The manual will help you run the tests to eliminate each one in turn before deciding to chance buying a new component. TBH on an old carb, I'd be tempted to track down some of these and fit them at the same time whilst the carb's off. Know it might be expensive, but probably less hassle. It'll then be future proof. A secondhand carb is a gamble in that it might be faulty gas well.

Has the bimetallic choke unit ever been removed before? In it is a copper coil that regulates the operation of the choke when cold starting. It expands with increasing temperature to take the choke off. The problem is that it always needs to be refitted at fridge temperature. If at room temp, the coil will be in a state of expansion that means that the carb choke setting is out when trying to start in cold winter temperatures. The effect of this is that the car will start at too much choke resulting in 3000 or so revs for a few minutes until the engine reaches operating temp, when it reduces to 1000 rpm.

The proper operation of a 2E2 carb from cold start is for the engine to go straight up to 2000-2500 rpm for about 5 seconds before instantly dropping to about 1500 rpm.



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scirockirb
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Re: Very High Idle - suspected waxstat

Post by scirockirb » Mon Jan 29, 2018 5:25 pm

I went through all the tests above with my pierburg including testing the waxstat as you have. I thought the waxstat was fine, I saw similar movement to your test.

On New Years Eve in the pub, I was chatting to a former VW Tech (in the 80's) and he said it would be the waxstat and said he'd pay for it if it didn't work. I was never going to hold him to that but it made me buy a new waxstat. How I wish I'd just bought it earlier... it was an instant fix. I took the new waxstat out and carried out the test... it moves a lot further than you would expect. It is an expensive part unfortunately and seems to be a regular problem causer!

I'm not saying it will be the same for you as I am in no way a pierburg expert, just sharing my similar experience. I now have a 2.0 16v ABF in its place btw which only added £60 to my insurance too.