Strange cold start on 84 4000 quattro

[Johnny B]

Is there anything vacuum related pertaining to the fuel system minus the small line running from the airbox to the FPR mounted towards the front of the box? 

I unplugged the coolant temp switch located near cylinders #1 / #2 on the neck leading in to the head. This got the car to fire but I noticed it still had the weird missing / throttle issue with it unplugged (even more so then standard cold start). I plugged the switch back in but at that point the car was warmed up enough that nothing was acting up anymore. Because it had the same symptoms with the switch disconnected I'm assuming the switch is not my answer. 

Even with the engine warm, if I park it for say 30-45 minutes (so, ambiently still warm) it will have the same issue on start where the idle seems smooth, until applying any throttle where it gets choppy, but eventually (30-45 seconds) works itself out and no issues after that (all the way to 4500rpm+). Other times, you will fire up after a few hours of sitting and no apparent problems what so ever, easy start, rev happy, no brick walls or cycling. 

The new thermo switch comes in the mail today, which i will toss in and hope for the best. Later this week my vac tubing & formed silicone tubes will arrive and during the install I plan to remove & clean the ISV, clean the throttle body & metering plate, and check everything over with chemtool for more leaks. After warmed up, I will do another check with the chemtool to see if anything is opening up at higher RPM / heat levels.

I ask about the vac system connected to the fuel supply as it almost seems that when I park an air bubble forms in the fuel line giving me the cold start issue when i go to refire (as this kind of feels like a diesel with a vac leak on the fuel system...). I noticed my fuel pump does not prime when you turn the key over to Acc (as all my other 4k's and CGT's have), but does kick on when cranking (so not sure if that has anything to do with this). 

After the vac tubes are all in, and everything has been cleaned up and checked over, I'll let everyone know where I stand and what I have to face then. 

For what its worth, the injectors & seals (and all gaskets on the engine) have been replaced. I found one large vacuum leak beneath the intake boot which i corrected, and it has helped my idle (now stable just shy of 1k, does not vary warm or cold) but still have this cold start problem present. 

Extremely frustrating knowing once started the car idles as it should, drives as it should, has no apparent issues what so ever, until you park and it gets cold. 

Johnny

> Date: Sun, 8 Aug 2010 18:03:12 -0400
> From: audi at humanspeakers.com
> To: proleonk at gmail.com
> CC: pre95 at live.com; quattro at audifans.com
> Subject: Re: Strange cold start on 84 4000 quattro
> 
> This definitely sounds like a lack of enrichment when cold, leading me 
> to suggest testing that NTC sender, measure resistance in ice water and 
> boiling (careful!) water.
> 
> I'm surprised that 2200 rpm cutoff doesn't slowly rise as it warms up, 
> though.  It's a bit too high to be a stuck idle (closed throttle) 
> switch, that makes a brick wall around 1400 rpm.
> 
> Someone suggested a vacuum leak, which although I don't think it is, it 
> can't hurt to carefully go over all your hoses and fittings.
> 
> On 8/8/2010 2:14 PM, DK wrote:
> > I had something similar happening to my 86. The coolant temp sensor
> > (for the ECU) developed a leak and coolant accumulated slowly at the
> > connector. Made the readings go haywire. Disconnect it next time it
> > happens to start troubleshooting. I tightened the sensor mine up and
> > cleaned the connectors and the problems where gone. My car usually
> > took around a minute till it acted normal and would fall flat on its
> > face when you tried to drive it.
> 
> -----
> 
> > The car turns over but doesnt fire. After letting it sit for a few
> > seconds, it turns over and coughs, but misses. More turning over and
> > then finally it fires and coughs to life. Very choppy but after a few
> > blips on the throttle it smooths out to a nice idle just above 1k rpm. I notice here when I blipped the
> > throttle a few times it sounded like the motor was bogging, and the intake was quite
> >  loud.
> >
> >
> >
> > I bring the RPM's up to 2k and its smooth, but at 2200 RPM it bogs
> > itself down and brings the RPM back to 2k. If I hold lightly on the
> > throttle bringing the RPM up it will cycle this (up to 2200, bog, back
> > down to 2k, up to 2200, bog, down to 2k etc etc). If you floor it, it
> > just bogs harder. After letting it idle (which during all of this it's
> > idling very smooth) 30-45 seconds, all symptoms go away. Runs smooth, rev's
> >  up as it should, all problems go away. There was no smoke at start up..
> >  I'm definitely stumped.....
> 
> 
> -- 
> Huw Powell
> 
> http://www.humanspeakers.com/audi
> 
> http://www.humanthoughts.org/