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I had it in the shop on Monday. Was told I needed a knock…

Hello, I had it...

Hello, I had it in the shop on Monday. Was told I needed a knock sensor, but they didn't have. On Tuesday, the car died on my wife and now won't start unless I push the gas and keep Rom above 1000 for about 1 minute. Then it will idle but surges.

Mechanic's Assistant: Which particular sensor are you asking about? And have any trouble codes been triggered?

I had a p1000 when I took it to the shop. This went away when they put in the missing screw from the pcv they left off before

Mechanic's Assistant: What is the model/year of your VW?

2010 cc

Mechanic's Assistant: Are you fixing your CC yourself? What have you tried so far?

Nothing yet, I have looked at mass air flow, but it's clean. Waa looking at the challenge to replace the knock sensor. Car ran great before the dealwr. Lol

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Engine only has about 10k miles on it and was replaced by the dealer. Victim of timing tensioner

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Answered in 43 minutes by:
3/16/2018
Danny
Danny, VW Mechanic
Category: VW
Satisfied Customers: 4,497
Experience: ASE Master Certified with L1 Certification, Volkswagen Certified, VW and Audi repair shop owner
Verified
Are you sure p1000 is correct, that's a fault code for the fuel injector for cylinder number 9 which you don't have 9 cylinders.
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Customer reply replied 4 months ago
Sorry, p0100. I had fault codes for the pcv before and replaced it and the intake tube along with the tube going to the turbo pipe.
If you want me to call I can, however I think it's probably not necessary that fault code says that the supply voltage to the mass airflow sensor is faulty. Check and see if the mass airflow sensor is still plugged in, it seems like it might not be or one of the intake pipes has come loose you probably have a giant vacuum leak somewhere.Something that you had loose or they have lose when the PCV system was replaced has come loose, so like check all the intake pipes up top to the throttle body and the PCV stuff check to make sure the mass airflow sensor still plugged in, have your wife sit in the car and start the vehicle while you're under the hood you should hear a giant vacuum leak and be able to find it pretty easy if the maf is plugged in and everything.
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Customer reply replied 4 months ago
I can do that, but I think all is plugged in. Like I said, pcv and was bad, and replaced. Still throwing code for the camshaft position sensor. Dealer diagnostics said the knock sensor was bad. Once missing screw was installed into pcv, check engine light went out. I ordered the part and was waiting for it to come in. Car will run if you hold rpm over 1k for about 1 minute then let idle, but it surges.
why didn't you give me the fault codes for the cam position sensor and stuff? Please give me all of the fault codes.Do you have a scan tool? If you do go in and scan tool and go to real-time values and look at the mass airflow sensor reading and give me the reading it idle or is close to idle as you can get it and then give me the reading at 2000 RPM while you're sitting stationary.The thing is that I get that to you it's kind of and uncertainty what could be wrong but from working on vehicles basically I know how the vehicle calculate how much air in fuel kitchen need to run and I know the things that cause a vehicle to die at idle but allow the vehicle to run at a higher RPM.Just a real quick explanation that might make it more understandable is like this.To calculate how much fuel did a vehicle needs the vehicle uses the coolant temp sensor, the mass air flow sensor, and the oxygen sensor. The oxygen sensor is really only used to double-check that the vehicle is adding the right amount of fuel based on the initial calculations and fueling.The oxygen sensor doesn't warm up for about a minute and become operational so for like a minute until oxygen sensor heater in the exhaust he the oxygen sensor up over a certain temperature it stays in what's called open loop fueling.Open loop fueling means that the vehicle engine control module is only using the coolant temp sensor and the mass airflow sensor to calculate fueling and since it can't double check that that's correct because oxygen sensor isn't online yet it just has to rely on those calculations so it just runs rich and adds more fuel than it needs to because running lean is detrimental to engine life.So the fact that the vehicle will not idle for about a minute tells me that the mass airflow sensor is not correctly reading the amount of air that entering the intake manifold. This means that either the mass airflow sensor is faulty, not working, or that there's a massive vacuum leak allowing ear to sneak in past the mass airflow sensor.There is a fault that says mass air flow sensor high input and that can either mean that there's something electrically wrong with the mass airflow sensor, or that the reading is so out of whack that the computer is getting returned essentially no voltage at times which would be caused by a massive vacuum leak.The thing about mass airflow sensors is that when they fail it's because they've gotten contamination on the wire in the housing and that throws the reading off, but it really only throws the reading off an appreciable amount above like 1500 RPM so the mass airflow sensor being actually faulty and causing an idle problem is highly unlikely.Also there is no coolant temp sensor fault, sold the most likely cause, especially being that it already happened once, is that one of the things that was touch wasn't put back on properly now might not be the PCV valve this time it might be that the intake boot blew off under boost because it wasn't tight or something like that.The reason it's still running poorly even after the auction sensor comes online is because the fuel trims only have a window of about 20% Which means the engine computer can really only compensate for the mass airflow sensors in correct reading up to 20% more or less fuel than what the initial calculations are telling it it should be adding, so with a failing mass air flow sensor it'll compensate because it reads, but when it's reading literally no air at idle because there's a giant vacuum leak that amount of fuel that it would need to add to properly meet the 14.7 to 1 air fuel ratio that is necessary and idle is outside of that 20% window.So there's some background on it but I'm pretty sure that it's a giant vacuum leak. The final reason is because if the mass airflow sensor is actually not plugged in at all with the engine computer does is looks at what the throttle body opening is and what the RPM of the engine is and it just assumes that the mass airflow sensor is reading perfectly and plugs in the amount of air that the engine should be reading at that RPM so I haven't unplugged would actually probably run better because it would just plug in that default amount for idle rather than looking at it and going oh I'm not reading any air and then actually calculating the air fuel ratio off of that extremely low value.
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The mass airflow sensor should be reading 3.5 grams per second at idle and 10.5 grams per second at 2000 RPM.But my guess is that when you open up the real-time sensor value and you look at the map that at idle is reading less than 2 grams per second of air
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Customer reply replied 4 months ago
Appreciate you getting back to me. I did have my wife start the car while looking for vacuum leaks. Found 1 vacuum line that looks like it goes to the n85, but it dis nothing to the surging. I think our communications are crossed somehow, if I maintain throttle above 1k for about a minute, it will idle after. Guess when the o2 sensor kicks in, but it's really rough, or surging. I cannot hear a vacuum leak. I know it's late, and since I really can't run the car right now, can we finish tomorrow? Also, for a scanner I only have a basic Mac tools code reader and it's not throwing codes at the moment.
The Mac Tools reader should read live values so you can get the mass air flow sensor values, even the lowest of the line of OBD scan tools that has a tool company name on it is going to be able to do it I have a bottom of the line Matco scan tool that works. It's going to be referred to as live readings or live values or real time sensors or something like that, and it should allow you to access the coolant temp sensor reading, MAF sensor, O2 sensor readings and whether or not it's an open or closed loop, throttle position sensor, basically all of them it might even give you the injector duty cycle... It's pretty standard for OBD2 scan tools.
Danny
Danny, VW Mechanic
Category: VW
Satisfied Customers: 4,497
Experience: ASE Master Certified with L1 Certification, Volkswagen Certified, VW and Audi repair shop owner
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Customer reply replied 4 months ago
Hello are you still around?
Customer reply replied 4 months ago
I now have codes, but only the p0300 series for misfire detection. They all come up. I have also been all over the car in search of a vacuum leak and not seen anything yet.
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