Replacing camshaft sensor; will CEL go off on its own?

[volkswagensRus]

Alright so here's the deal. Bought the car under the pretense that the camshaft sensor is shot. I somewhat knew the guy, he's honest and straight forward. He's also owned ~15 1.8t cars, and worked for 3 years at teh local top-notch Volkswagen dealership.

The car has a CEL
The car can sometimes take 2-4 times to start
Once it starts, the idle stinks and kinda bounces around


I'm pretty sure it's the cam sensor. SO. After I replace said sensor, will the car immediately start up properly, idle properly, and the CEL go off on its own? The car isn't technically on the road, and wont be for another few weeks. If all it takes is driving for the CEL to go off, I'll have to wait for it to go off. The local advanced auto claims they aren't allowed to turn CEL's off anymore and I dont own vcds yet.

[iamshayan]

Just unplug your battery after.

Make sure your timing is lined up properly because that will throw a cps code too.

[volkswagensRus]

Will do. I'm very lacking on tools now a days; most have been lost to "borrowers" or during my many moves. So basically IF my problem is the cam sensor, once it's plugged in my issues will go away right away right? The car will fire up on the first try, the idle will be gentle, etc?

[valleycruiser]

Just so you know, a leaking vacuum hose causes the exact same symtoms. To test, just get a can of flammable fluid and spray in obvious locations while idling (most vacuum) and the engine will rev high quickly when a vacuum is found. this should only be done with a friend beside you with ABC type fire extinguisher. Don't forget to test along the intake manifold gasket because that's where mine was, we just used gasket sealer compound while engine running to suck the stuff in, worked great, ten minute fix.

[volkswagensRus]

Even if there is a CEL for cam sensor? The previous owner, an acquantaince, says that a scan said it was the cam sensor. I'll definitely look at the vacuum lines too, good call on that.

[crazyquik22023]

99% of the time a cam sensor code is unrelated to the cam sensor itself. Most of the time the code will come up if your timing is off. From the sound of your problems I'd bet that your cam to cam timing is off a tooth.

[volkswagensRus]

Interesting! Well I already ordered the darn thing from Pelican Parts; I guess I'll just install the thing and see what happens, and if my idle/startup isn't instantly fixed I'll grab my buddy w/ better tools and VCDS and check the timing of the cams. How would this have jumped though??

[crazyquik22023]

More than likely previous owner attempted to replace the cam chain tensioner and did not install the cams correctly. When you do it make sure you count 16 links in between each cam arrow. There are MANY picture and diy's you can find on it.

[walky_talky20]

The 2-4 times to start is exactly the behavior you get if you run a 1.8T with the cam sensor unplugged. Sometimes you'll even get it to backfire. Try it sometime.

Basically the ECU is able to tell where TDC is based on the crank sensor, but it can't tell what 'stroke' the engine is on. So it just "guesses". About half the time (or less) it is correct and the engine starts and runs. The other half of the time you get a no-start. It will be injecting fuel on the power stroke and firing the plugs on the exhaust stroke. So your mechanical timing (belt and chain) are perfectly fine, but your spark and fuel are 180 degrees out.

Failure of the sensor itself is not super-common, really. Failure of the wires to the sensor is probably a bit more common. But either is possible.

[volkswagensRus]

Great advice guys. I happened to check earlier and the cam sensor LOOKS to be plugged in just fine. I already ordered one from pelican parts; worst that happens is it changes nothing. My buddy offered to bring vcds by on friday to assess what is happening. Thank you much for the information to mull on.

[volkswagensRus]

To update this. Since installing cam sensor, the car starts up RIGHT away (no extended cranking, no 2, 3 and 4x of trying to start it). It idles VERY smooth. It revs FAST and not lazy any more. It has certain power while wot, and it seems to lug gear to gear better.

The mechanic scanned the car and the only remaining reason (he claims) the CEL is on is due to a leak in the flexpipe of my stock downpipe.... which I know about. So I think we can wrap this up fellas.


PS the old cam sensor said it was Bosch but made in china... the new one from Pelican Parts mentions nothing about china.

[Wrath And Tears]

The mechanic scanned the car and the only remaining reason (he claims) the CEL is on is due to a leak in the flexpipe of my stock downpipe.... which I know about. So I think we can wrap this up fellas.

The flex pipe is pretty far away from the rear O2S. I don't think air entering through there would cause the rear O2S to report a lean condition causing a CEL, which is what the tech is assuming. Air usually has to enter before the rear O2S.

[volkswagensRus]

I wish he would have given me the exact code now. I was under the impression the flexpipe was indeed between the 2 o2 sensors though? I guess I'd have to look.

[volkswagensRus]

Small update; seems you guys were right. It's more than just the cam sensor. Vagcom scans say that the timing belt is off some teeth and causing misfires. This explains why sometimes when the motor is cold it has a sort of "cammed engine" idle to it. I figure if I'm going to redo the timing, I'm going to get a fresh timing kit also. Will keep you updated.

Quick question; downsides of the timing off a tooth or two? Low mpg, low on power, funky idle... is that about it?

[Wrath And Tears]

I wish he would have given me the exact code now. I was under the impression the flexpipe was indeed between the 2 o2 sensors though? I guess I'd have to look.

On 1.8T the cat is located right behind the turbocharger and both oxygen sensors connect to the cat. The flex pipe is at the greatest bend in the exhaust, a foot or two behind where the exhaust connects to the cat.

Well for the AEB any way.... Since you have the AWM it looks like I'm completely wrong, or google lied...

[volkswagensRus]

My buddy looked at the cat; says its aftermarket. Also the flexpipe is aftermarket, which is why it's rusted away he said. The flexpipe on my awm is probably a good 1.5-2' back from the cat, yes. I looked at the codes and it says NOTHING about an o2 sensor, so I dont know wtf teh shop was seeing lol.

[crazyquik22023]

Small update; seems you guys were right. It's more than just the cam sensor. Vagcom scans say that the timing belt is off some teeth and causing misfires. This explains why sometimes when the motor is cold it has a sort of "cammed engine" idle to it. I figure if I'm going to redo the timing, I'm going to get a fresh timing kit also. Will keep you updated.

Quick question; downsides of the timing off a tooth or two? Low mpg, low on power, funky idle... is that about it?

Figure out why your timing is off a tooth and fix immediately. 1.8t crank to cam timing can be off 2-3 teeth at most without piston to valve interference. You said in your first post that the car idled properly after it started, now you are saying it sounds like a "cammed" engine? Vagcom also does not tell you that your timing belt is off. Here is what you should do. Crank engine over by hand 19mm 12 point socket by the crank and line up the mark on the cam gear to the mark on the valve cover when that is lined up check the mark on the crank pulley to the mark on the lower timing cover. If marks don't line up, replace timing belt, tensioner, and water pump and time properly. If both marks are lined up, leave engine in this position and remove valve cover and check cam to cam timing. Should be 16 links in between each cam mark.

[volkswagensRus]

The codes thrown in vagcom basically said, going off memory, random misfires, timing, etc. My good buddy who's a huge audi head (owned countless 1.8t's and S4's) said its the classical symptom that timing is off a tooth or two. I'm ordering a full timing kit for the hell of it and we're going to check everything out and get it running.

When the car is COLD, ie the first start of the day, it idles "bmm, bmm, bmm, bmm" instead of a smooth, unnoticeable idle. It goes away after the motor warms up a minute or two. Back when I first got the car and after the initial cam sensor swap, there wasn't any idle issues. Albeit was a touch warmer outside too. I'm not driving it until the timing belt and timing are all squared away though.

[volkswagensRus]

Just as an update. Replaced the cam sensor. This helped some things for SURE. Then went to redo timing belt w/ all new equipment; this was spot on. It turns out to be the cam tensioner under the valve cover. Going to buy one soon and replace that.

I'm guessing that since the tensioner is off (the code is showing an over-retarded cam code), i could be missing out on power and mpg aside from the obvious cold-start issues?