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Cold startup fiasco

730 Views 6 Replies 3 Participants Last post by  wolfsburger
I am having cold startup problems in the last 4 week. The engine catches up only after 2-3 times. Some of the times it misses on the fuel rich cycle mode and immediatly turns at 900 RPM.
The VAG Service garage has found no errors on the computer!
I have lefted the car overnight in the garage with a fuel compresion gauge on the fuel line.
In the morning we have found the pressure to be normal, 2.0 Bars.
We checked the water temperature sensor, it was normal and has read the ambient temperature, 14 C.
We checked the throtle and found it performing normal. Minimum setting 4.9 degrees.
We have looked at the spark plugs and found them OK.
We disconected the water temperature sensor and connected a resistor to transmit the ECU a hot (92 C ) reading. We tried to start the engine and it started up as if already hot! As the engine ran we have disconnected the resistor and connected the water temperature sensor again. The ECU immediatly has understood the cold water reading and turned into a fuel rich mode, i.e. the rounds went up to 1200 RPM and the secondary air pump has started up.
The technician has decided that my ECU has a problem and has ordered a replacement. He explained to me that the ECU probably does not translate the cold water temperature reading into a fuel rich mode when I startup the engine from cold.
What do you think?

[Modified by primekart, 4:03 PM 11-30-2001]
1 - 7 of 7 Posts
Re: Cold startup fiasco (primekart)

have them show you the water temp datablock log from their vag tool. It may be a harness or wire issue as well..
Re: Cold startup fiasco (mrkrad)

I stood near the technician all the time and saw the whole operation. No harness problem. That's for sure.
Re: Cold startup fiasco (primekart)

Now that I realy do not understand! The first cold startup after the garage check the engine started like new! The problem has vanished!
Can someone explain me what has happened here? Did the technician has done a "boot" operation to the ECU without being aware? Will the problem return?
Re: Cold startup fiasco (primekart)

I used to have the same problem, but now it has come and gone. Once in a while I would have the cold start problem, and sometimes I would not.
Now I learned that if you put the key in the ignition and turn it to run (without starting) for about 5 or 6 seconds and then start the car. This has eliminated the problem for me.
I know it works because one morning I forgot to leave it on run for a few seconds and tried starting it without...
Problem came back for that start. After that I did it again waiting and it was gone. Now I just do that and it works fine. http://****************.com/smile/emthup.gif
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Re: Cold startup fiasco (wolfsburger)

You must have low fuel pressure problem in the morning. You should check the accumulator valve or the regulator. You should have a pressure of 2 Bars in the morning. When you wait before startup you are just building up the fuel pressure back!
It was the first thing to be checked iN my car and was found OK!
Re: Cold startup fiasco (primekart)

Thanks for the suggestion, I have to go in for a oil change real soon, so I'll ask them to check that out and see if it is the problem. They can also fix my dash that they chipped last time it was in...
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