Volkswagen Passat Forum banner

1 - 20 of 35 Posts

·
Registered
Joined
·
15 Posts
Discussion Starter #1
1.8T AWM w/ 155,000

About two months ago my car began to take longer (more cranks) to start in the morning (or after sitting for 4+ hours). Now for the last three weeks the car will only start on the second attempt meaning (I can let it crank and crank and crank - nothing. I switch the ignition off and try again and it starts). However, once it starts on the second attempt it runs rough and will die if I try to release the clutch and try to move the car. If I let it sit and bring the RPM's up to 1K for 10-20 seconds then I can release the clutch and begin driving.

After the initial 10-20 seconds after starting the car behaves and responds normally. Full acceleration and normal idle. Maybe slight hesitation if I blip the pedal.

Symptoms do not change if I try to "prime" the fuel system multiple times. I checked the fuel pump relay which supplies correct voltage back at the pump. I manually operated the fuel pump with a battery charger and it spins right up with some noise.

CTS appear to be working normally via VCDS.

MAF appears to be normal via VCDS.

Spark plugs have 6-8k on them and are the original spec Denso plugs (from what I researched these are OEM just rebranded by VW)

I have been researching and reading online for a few days and no one seems to come up with anything conclusive.

Thanks in advance
 

·
Registered
Joined
·
45 Posts
Replace crank sensor. It was a long fought battle for me of very similar symptoms. Try it as they are cheap. Mine would do nearly the exact same.
 

·
Registered
Joined
·
45 Posts
Also all my other none vws would die when warm when the crank sensor was bad. My 03 passat was the opposite of all prior experiences with none vw. It had issues cold or cool. It always started after a bit of cranking. Second or third time. Run it for a bit it would smooth out and be great. Stop at gas station it would start right up. Next morning crank, crank again, start kinda stumble and miss, warm up a touch smooth out be great. Dead serious replace crank sensor.
 

·
in dire need of an organic chemistry lesson
Joined
·
2,285 Posts
The speed sensor indeed could be a culprit but with one caveat. In the beginning when it goes bad the car should crank a couple of times to start. But as the time passes the number of cranks increases and at certain point it won't start no matter how many cranks. I don't think you can go months They die pretty much after a few weeks. The best bet is to scan the codes and see if it mentions any intermittent signals related to the sensor. If so then change it otherwise you need to search the cause in other components.
 

·
Registered
Joined
·
45 Posts
When mine was acting up it did it one day and never changed this for over 6 months as I messed with every other possibility trying to get it fixed. This was the car the girlfriend was driving. I never threw a code except misfire codes a few times. Nothing at all indicating crank sensor. I changed it on a last ditch effort and it was instantaneously fixed. If it's a weakness in the magnet or a temperature thing based on expansion vs contraction idk All I know is it instantly cured my issues. There was no progression or worsening just one day it did it. I spent alot trying to fix that and I'm trying to save someone a headache. Can I say 100% that's what it is well no. But after my experiences I most certainly would order one and install it before I put any thing else on.
 

·
in dire need of an organic chemistry lesson
Joined
·
2,285 Posts
I'm trying to save someone a headache. Can I say 100% that's what it is well no. But after my experiences I most certainly would order one and install it before I put any thing else on.
We had several people on this forum who had issues and changed the speed sensor without their problem resolved ending with an unnecessary cost. If the sensor goes bad it definitely causes error codes that can be read. It is always better to do a proper diagnostics before proceeding.

To the OP: it is likely that your speed sensor is dying. But it would be better to scan the codes again and see if indeed you get faulty signal from it. The sensor itself is not expensive but replacing it, is a PITA.
 

·
Registered
Joined
·
26,187 Posts
Since it seems you have VCDS, I would expect there are no codes to report. In this case, I agree it would be the crank sensor as they often start to fail without throwing a code. I would say replacement is a hassle, but not a PITA. It's a lot easier than the PCV, but not as easy as checking the oil. With good light and a mirror, it's not too bad.
 

·
Registered
Joined
·
15 Posts
Discussion Starter #8
So I replaced the crank sensor yesterday and...... still struggled to start this morning. My idle definitely smoothed out (less vibration at idle) since replacing the sensor but still hard to start when cold. I just went to lunch and after sitting for 5 hours it again took two attempts to start.

There are no codes that have been triggered or stored since this all began.
 

·
Registered
Joined
·
15 Posts
Discussion Starter #9
I am confused as to why there is no code with the difficulty starting each morning/4+ hours of sitting.

Anything else i can check with VCDS to help find the problem?
 

·
Registered
Joined
·
26,187 Posts
You can run misfire counts on each cylinder when starting. It will show misfires that do not trip the CEL. If they are equal on multiple or a single cylinder, it may be low fuel pressure, dirty injectors or leaking injectors. You can also try cleaning the throttle body as it can screw up the idle air flow. I would also check the vacuum, I have had cars that leaked vacuum from the brake booster or the line to the vacuum tank and they would run rough on starting as the vacuum was depleted.
 

·
Registered
Joined
·
15 Posts
Discussion Starter #11
I tried to look up the misfire counts but it said it was disabled in VCDS. How do I enable the count?

Also, does anyone have a diagram of the vacuum system on a 1.8t AWM?
 

·
Registered
Joined
·
26,187 Posts
I don't know how to enable the count in VCDS.
The diagrams for the vacuum hoses are mostly dead due to Photobucket now blurring all of their pictures. These links might help:



 

·
Registered
Joined
·
15 Posts
Discussion Starter #13
Just found another clue this morning. Once I got it started if I depressed the brake pedal my RPM's significantly dropped.. I'm talking 200 RPM. Guessing this is because of a lack of vacuum?
 

·
Administrator
Joined
·
23,351 Posts
You can run misfire counts on each cylinder when starting. It will show misfires that do not trip the CEL. If they are equal on multiple or a single cylinder, it may be low fuel pressure, dirty injectors or leaking injectors. You can also try cleaning the throttle body as it can screw up the idle air flow. I would also check the vacuum, I have had cars that leaked vacuum from the brake booster or the line to the vacuum tank and they would run rough on starting as the vacuum was depleted.
Just found another clue this morning. Once I got it started if I depressed the brake pedal my RPM's significantly dropped.. I'm talking 200 RPM. Guessing this is because of a lack of vacuum?
We might be on to something here. check all valves and connections from the booster to source of vacuum. Suction Jet Pump, check valve to vacuum reservoir, and hoses/lines
 

·
Registered
Joined
·
15 Posts
Discussion Starter #15
So I have checked all of the lines and valves that I can see and I am unable to detect any cracks or leaks. I had a friend recommend spraying soapy water all over the vacuum lines/valves and seeing if it temporarily improved symptoms but that had no effect.

As it has been colder at night it is getting hard and harder to start in the morning. Now taking 3-4 attempts.

Any other ideas?

The decrease in RPM's with brake depressed only happens shortly after I get it started. Once it ran and warmed up there is no change in RPM's when I depress the brake pedal
 

·
Registered
Joined
·
15 Posts
Discussion Starter #16
Also, if I disconnect the brake booster line that connects to the firewall the car will not start.
 

·
Registered
Joined
·
26,187 Posts
For vacuum leaks, soapy water would make bubbles inside the hoses. You can try spraying carb cleaner around the hoses and see if the rpm rise. I have not had much luck with that.
I would try capping the vacuum outlet to the brake booster after the car sits overnight. Then see if starting the car is easier. If the car starts normally, you have a leak in the booster. Do the same for the vacuum reservoir (1 hard line under the coolant tank and 1 hard line behind the coolant tank, they meet at the reservoir).
 

·
Registered
Joined
·
15 Posts
Discussion Starter #19
For vacuum leaks, soapy water would make bubbles inside the hoses. You can try spraying carb cleaner around the hoses and see if the rpm rise. I have not had much luck with that.
I would try capping the vacuum outlet to the brake booster after the car sits overnight. Then see if starting the car is easier. If the car starts normally, you have a leak in the booster. Do the same for the vacuum reservoir (1 hard line under the coolant tank and 1 hard line behind the coolant tank, they meet at the reservoir).

So I replaced the 4 vacuum lines that everyone says are typically the culprit. Started very rough which I expect after depleting all the vacuum. I will wait a few hours and try again later.

I was going to replace the set of hoses with multiple check valves (Just under the intake manifold) but those seem to be larger diameter? I bought the 3.5mm vac hose.
 

·
Registered
Joined
·
15 Posts
Discussion Starter #20
For vacuum leaks, soapy water would make bubbles inside the hoses. You can try spraying carb cleaner around the hoses and see if the rpm rise. I have not had much luck with that.
I would try capping the vacuum outlet to the brake booster after the car sits overnight. Then see if starting the car is easier. If the car starts normally, you have a leak in the booster. Do the same for the vacuum reservoir (1 hard line under the coolant tank and 1 hard line behind the coolant tank, they meet at the reservoir).
What would you recommend plugging the brake booster line with? I can’t seem to think of anything I have on hand
 
1 - 20 of 35 Posts
Top