Rough idle at cold start

RyanRodman · Posted: Sun Nov 22, 2009 3:22 pm Post subject: Rough idle at cold start

I have a 1969 FI fastback and at a cold start it idles real low and rough and sounds like it almost wants to die, but after a minute or so when it is warmed up it will start to idle perfectly. It has new plugs, wires, points, fuel lines, fuel pump, and injector. Any ideas? Thanks.

blankmange · Posted: Sun Nov 22, 2009 3:23 pm Post subject:

vacuum leak...
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Russ Wolfe · Posted: Sun Nov 22, 2009 3:37 pm Post subject:

Or AAR is not opening when cold.
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Society is like stew. If you don't keep it stirred up, you end up with a lot of scum on the top!--Edward Abbey

Gary: OK. Ima poop.

RyanRodman · Posted: Sun Nov 22, 2009 10:15 pm Post subject:

KTPhil · Posted: Sun Nov 22, 2009 11:26 pm Post subject:

Take it out, clean it, and then adjust it.
Image may have been reduced in size. Click image to view fullscreen.

I actually tweaked it a little more open from this adjustment to improve the cold idle a bit. I made sure it was closed after about 5 minutes or less. Most of them actually bleed a bit of air even when "closed" but that is easily compensated for with the regular idle screw.

RyanRodman · Posted: Mon Nov 30, 2009 7:56 am Post subject:

Ok, so over the weekend i took out the AAR, I adjusted and clean it. Now it idles high and good like it should for about 10 seconds after you start it, then the idle goes down and is just a little rough before it smooths out. What else might it be? The AAR does stop sucking after about 10 minutes or once the motor is warm, so i dont think there is anything wrong with it. Any more ideas?

raygreenwood · Posted: Mon Nov 30, 2009 8:20 am Post subject:

You still have a vacuum leak somewhere. In reality...the AAR when all is perfectly adjusted ....does not cause a high idle. Without the AAR as a extra source of air to mix with the overly rich fuel mixture at idle/start-up....the car generally will not idle at all unless the outside temperature is fairly high.

Its designed to cause the engine to idle at the normal idle speed with no troubles. Because of the range of adjustment of baseline fuel mixture that was common from the factory...and the condition and differences of the engines.....it may in some cases cause an idle just "slightly"higher than spec.
I mean like maybe 100 rpm or so.
In any case...its not fast enough in reponse time to have any effect over 10 seconds time. 5-8 minutes in more standard due to oil temperature.

Either a vacuum leak in an oily or fast heating area that seals up quick...like at the runner to head joint.....or an excess of fuel in the ports due to leaking injectors is usually the cause of what you are seeing. RAy

RyanRodman · Posted: Mon Nov 30, 2009 11:58 am Post subject:

RyanRodman · Posted: Tue Dec 01, 2009 7:09 pm Post subject:

I have heard that you can spray a little starting fluid on spots where you think you might have a vacuum leak and the engine will rev a little and thats how you will know if you have a leak. Has anyone tried this? Thanks again.

Russ Wolfe · Posted: Tue Dec 01, 2009 9:37 pm Post subject:

I would not use starting fluid. Too flammable. I have used carb cleaner, Brake clean, WD40, and propane.
_________________
Society is like stew. If you don't keep it stirred up, you end up with a lot of scum on the top!--Edward Abbey

Gary: OK. Ima poop.

RyanRodman · Posted: Tue Dec 01, 2009 9:46 pm Post subject:

RyanRodman · Posted: Fri Dec 04, 2009 4:34 pm Post subject:

I still cant find the vacuum leak. Are there any common places where it leaks that i should check? Its really annoying having it rev up and down up and down at a stoplight like it is.

Bobnotch · Posted: Sat Dec 05, 2009 11:11 am Post subject:

RyanRodman · Posted: Tue Dec 08, 2009 4:14 pm Post subject:

So yesterday while tinkering with the AAR i dropped the and lost the tiny screw that holds its adjustment, Twisted Evil

so now i cant get it to hold an adjustment. I called a wrecking yard from my area and they say they have a '71, and 72' type 3. Would an AAR from these work. I think there was more wrong with my AAR than worth fixing when i could just get another one and hope it works. Also i am well do for a valve adjustment, do you think any of my problems could be solved by doing so? And also my dad doesnt seem to think that the fluctuating idle is a vacuum leak so...? Any more ideas? Thanks

KTPhil · Posted: Tue Dec 08, 2009 5:01 pm Post subject:

Cold start injector only comes on when it is REALLY cold and then only while cranking.

All mechanical AARs for VWs are the same; any of them will work. Automatic tranny style (electric) can be made to work, too.

How familiar is your dad with the D-Jetronic system specifically? Unless he is very familiar, you should politely ignore his advice and stick with the folks here. It is so simple it becomes non-intuitive for someone who knows the more modern and complex systems! Things like "vacuum leaks causing richness" drive those new to D-Jet nuts!

RyanRodman · Posted: Tue Dec 08, 2009 5:14 pm Post subject:

KTPhil · Posted: Tue Dec 08, 2009 9:29 pm Post subject:

Early cars lacked the cold start injector, but it was available as a retrofit. Again, though, it has nothing to do with idle, only cranking. Activation temps varied from 5F to 50F.

It is wired to the starter (terminal 50), which is why plugging it into the wrong terminal at the solenoid can make it run rich, since it then injects when cold and running, not just cranking.

RyanRodman · Posted: Sat Dec 12, 2009 5:18 pm Post subject:

Today i went to a wrecking yard and got an AAR off a '72 squareback. It is exactly the same except it fastened to the engine a little different. Before, my '69 had an electrical plug on the end of a bolt that threaded in to hold one side of the aar on and just a nut on the other. This aar from the '72 was just two nuts no electrical plug. Of course my bolt with the electrical plug broke Evil or Very Mad

, so now i just have it with a bolt on one side and a nut on the other. It works ok but is still a little rough until it warms up. So does that mean my '69 had an electrical AAR and the '72 had a mecahnical? Because it seems like it should be the other way around. Thanks. Oh and there seems to be no more vacuum leak, the idle does not wander. Very Happy

Russ Wolfe · Posted: Sat Dec 12, 2009 5:26 pm Post subject:

That bolt with the electrical plug is you oil temp sensor.

You should have that plugged in.
In the 72, they moved it to the air intake distributor.
The AAR is the same.
_________________
Society is like stew. If you don't keep it stirred up, you end up with a lot of scum on the top!--Edward Abbey

Gary: OK. Ima poop.

RyanRodman · Posted: Sat Dec 12, 2009 5:29 pm Post subject:

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