High Idle Speed

[TNovello]

I have a 1988 VW T25 and recently fitted a second hand 1.9 DG engine with the same Pierburg 2E3 Carburettor, that was installed with the old engine.

I fitted new leads, plugs, dizzy cap and rotor arm. When I start the engine the choke flap is at the correct setting after depressing the accelerator pedal and engine seems to idle correctly.

When the choke comes off (choke flap fully open) the engine idle speed increases to 1600 rpm, which I would expect to only be around 950rpm. I have tried setting the idle adjustment screw, which increases the revs one way but when turned anti clockwise the idle speed doesn't decrease, no difference is made, feel like I'm just unscrewing the idle screw until it comes off.

Next thing was to check the timing, when disconnecting vacuum hose from dizzy the revs dropped to 900rpm, so I set the timing 6 BDTC at this idle speed, but as soon as I connected the vacuum hose the revs went straight up to 1600rpm at idle, which again I would only expect to increase to around 950rpm.

I have tried searching for this issue but can't find anything that specifically relates, only the opposite where idle speed is low.

I'm new to these engines and at a bit of a loss as where to start and don't want to randomly start adjusting more settings, making things worse.

I would be ever so grateful if someone can point me in the right direction on what could be causing this?

Seems strange that with the vac pipe off the idle speed is correct, but high when connected, I can't think what could cause this.

Any help would be great! Thanks.

[neil3965]

Hi there

I'm afraid I have no experience of DG engines or Pierburg carbs, but my advice would be to hit google until you find a forum post, manual, exploded diagram or whatever that let's you work out how the choke / fast idle mechanism operates, and set the thing up from scratch. If it was a Solex, I'd say it might be getting stuck on the fast idle cam.

There's a lot of good info to be found on th following forums:

thesamba.com

Brick-yard.co.uk

Good luck!

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[TNovello]

Thanks Neil, I have searched Google until I can't look at the screen any longer and there is a lot of information. Most issues I found was for poor idling, low rpm, cutting out, but not much for high rpm, but I will try another search.

One thing I do want to look at is the fast idle cam adjustment, which I will do some more research and let you know how I get on.

Ads, do you have the same issue? I also have an Auto gearbox, not sure if this makes a difference to idle speed?

[kevtherev]

Your fast idle cam could be sticking on.
Some lube should sort it out.
The carb is best removed to do this, as you can check that the springs are in place and the cam is not seized
search my posts for "Fast Idle"
There's a lot of information there
Also your auto box peirburg carb is slightly different to standard I believe.

I would also be considering an air leak into the induction side.
This would increase rpm also

[TNovello]

Thanks for the reply Kev, I will be removing the carb and check the Cam operation, I've also checked your previous posts, which is very helpful.

The one thing I can't get my head around is the van idle's correctly at 900 rpm when the vacuum pipe is disconnected, but once connected goes up to 1600 rpm. Is the fast idle cam affected by the vacuum unit?

So what I will do is remove carb, check fast idle cam operation, clean carb, refit, set to correct cam adjustment and also replace all vacuum hoses going in and out of carb to be sure. Brake servo hose seems to be okay.

The auto choke seems to operate as it should and the timing is correct when vacuum hose disconnected. I have a new fuel filter which I will also fit incase this is causing issues.

I will let you know how I get on, thanks for the advice.

[irishbruce]

I'm experiencing a similar issue. WBX 1.9DG, 1990. Pierburg 2e3. Had the carb off to clean it, and fit a new needle valve and float. new gaskets and reassembled and refitted. On starting from cold, the choke does its job. engine settles to a normal idle after a few minutes. After driving for a mile or two, the engine races at idle. I initially thought it was a cable issue, but this seems OK. If I switch off and restart, the engine idles then correctly. Mystified, but must be something I did inadvertently when either reassembling or refitting the carb. (I assume).

[CJH]

I'm experiencing a similar issue. WBX 1.9DG, 1990. Pierburg 2e3. Had the carb off to clean it, and fit a new needle valve and float. new gaskets and reassembled and refitted. On starting from cold, the choke does its job. engine settles to a normal idle after a few minutes. After driving for a mile or two, the engine races at idle. I initially thought it was a cable issue, but this seems OK. If I switch off and restart, the engine idles then correctly. Mystified, but must be something I did inadvertently when either reassembling or refitting the carb. (I assume).

Interesting - I've had exactly the same experience. I bought a second hand carb of unknown origin, stripped it, cleaned it, and put a service kit on it. When I tried it on my engine it started and ran fine, but as it warmed up the revs just kept on increasing. I backed off the idle speed adjustment screw until it was no longer touching, and it made no difference. I must admit I just put it down to poor adjustment of the idle mixture control screw (since I had no idea whether it was running properly before I bought it) and decided it was best left to the experts to adjust that on a gas analyser. I then put the original carb back on and forgot about it.

Did you by any chance adjust the idle mixture control screw? Would this cause fast idling?

[irishbruce]

No, I didn't adjust any settings on the carb (knowingly). But of course, removing, splitting, reassembling and refitting will have caused some disruption, even if I didn't set out to make those kind of changes in the beginning. Odd that it resets itself after restarting.

[CJH]

Odd that it resets itself after restarting.

Oh, I didn't spot that. I didn't try that. Sounds choke-related.

[irishbruce]

Took the carb off again this evening, removed the choke unit, cleaned lubricated the external springs, shaft and cam mechanism and refitted everything. Adjusted the choke flap gap to 3mm - although it wasn't far off. Took the van for a run, and the same problem occurred as before. Running fine on the open road, and then the engine "raced" at idle. Continued driving, and after a mile it settled to normal on its own. Puzzling.

[kevtherev]

OK
If it's settling down a bit later then you can adjust the time it takes the fast idle to come off.
On the autochoke housing there are three screws, if you loosen them and turn the housing clock wise 5mm it should bring the fast idle cam around.

remember to mark the original position if you intend to move it back

[irishbruce]

Thanks kevtherev. I'll try this and see. However, I assume if this was the sole issue, the engine would be running too fast constantly? In this case the over revving problem can occur later as well, ie after the engine has been running normally for a few miles. Today, I travelled ten miles from cold with no issue and the engine idling as it should. But at the next traffic lights as I pulled to a halt, it was clear the engine was racing again. Blipping the throttle does not improve matters.

[kevtherev]

I think next step is to look at your throttle cable perhaps
The only reason it will intermittently idle high is if there is air getting into the manifold, by it's nature yours is telling me the butterfly valve is either opening slightly or the valve spindle is worn, creating this odd behaviour.
it's almost impossible to diagnose these things accurately remotely I'm sure you'll agree.


when it happens again I would be taking the duct off and looking at the valve, maybe poking a pencil at it to see if it is properly shut.

[irishbruce]

Cable seems to move freely. Would leaving it ( given the intermittent nature of the issue) cause any long term problems?