Constant slight bucking... help?

[MisterTurbonium]

Thanks in advance for any advice here.

My 2000 1.8t beetle has a problem where the power output of the engine is constantly changing. I feel it as a slight bucking while cruising, and occasionally as a strong bucking during acceleration from stop. Even at idle you can feel the car kind of jerk a little bit sometimes.

The is no CEL, but I hooked up my scanner to be sure and it indicates no codes.

I did some googling and decided the likely culprit is the MAF, and as they said to do I unplugged it to see if the problem went away. It did not; the car instead would stall soon after idling. Also, I don't know if this matters, but it took a lot of cranking to get the car to start after I plugged it back in.

One last hint: it was pretty warm one day last week and on that day I didn't feel anything wrong.

Any ideas? Thanks!

[norcalturbobug]

i have the same year beetle...with the same problem. every time i turn the ignition on in the morning there is some strange "fan" noise that comes on...at idle its not steady...jumps from 1 to 2k and continues through all the gears. think we have the same problem..i never got any cel except one time P0118 came up, i cleared it and it never came back...my problem comes and goes...i think its the coolant temp sensor...i changed mine and it seems to have done the trick...its a 20 dollar part from VW...makes sure to change the o ring...cheap fix...let me know if this helps..i just changed the sensor this afternoon and so far no problems...will let you know if the problems comes back...good luck!!

[pfeifervw]

My first guess would be that the vacuum/PCV lines are shot, because they don't hold air, the various sensors don't get accurate readings, and false air is brought into the intake manifold that hasn't been metered by the MAF.


Good luck!
Matt

[MisterTurbonium]

Thanks, both of you, for getting back to me. I replaced the coolant temp sensor long ago with the good green one, when my temp light would never go off.

As for the PCV stuff, you may be onto something. I did some googling and found another site where someone mentioned his throttle body and intake being covered in oil and said the PCV is to blame. I was poking around my engine recently and saw the same thing. The air pipe just before the TB has a nice coating of oil inside, and the temp sensor just after the TB was also oily. I'll take a better look at my car's PCV lines tomorrow morning.

[pfeifervw]

Correct me if I'm wrong, but a little bit of oil inside the TB and air intake hose is completely normal. A little bit of oil will inevitably slip past the seals in the turbocharger, and I always find a little bit in the bottom of the intercooler whenever i remove mine (and as far as I know, my turbo is perfectly healthy). A leak or blockage however would cause these problems. After about 60,000 miles, my vacuum lines were completely shot and needed replacing, doing this myself cost about $15. Another very common leak location is the PCV hose that comes out of the drivers side of the valve cover, mine tore around 75,000 miles.

[MisterTurbonium]

I just got in from poking around under the hood, and I don't see anything obviously wrong with the PCV hoses. Granted not all of them are very visible with the secondary air system right on top, but everything I could see looked ok to my eyes. Threw on a new breather valve I had laying around, just in case; no improvement.

Secondary air pipes look fine too, since I mentioned them.

I replaced all the fabric covered vac lines above the engine with non-cloth about two years ago, and they still look good. The black part of the black and white check valve goes to the front, right?

[OneFiftyThree]

Mine has had a surge at part throttle since new. I always thought it was the computer controlling the throttle by wire, or some other engine management issue: IE wastegate - blow off

???

[norcalturbobug]

well i finally figured out what was wrong with my beetle...one of my coils went out...i changed it out (19.99 at o'riely's) now it runs perfect! will a bad coil cause it to "buck"? my problem was interment..one day it would do then the next it was gone. well now that i changed the coil pack it runs outstanding!!

[MisterTurbonium]

My coils are still original (140k miles). I wasn't suspecting them because, like you, some days are fine (hot ones).

[norcalturbobug]

i have around the same mileage...really i would never have figured this one out if not for the coil going out....that too and the plugs where so bad its not even funny...i have only had the car for a little over a month...and really this is the reason the previous owner sold the car so cheap is because no one could figure out why the car was running so rough. the coils where so cheap ($19 at o'riely's/kragen with a life time warranty!) but maybe you should try the plugs first...good luck hope it turns out.

[pfeifervw]

I'd definately give coils a shot (and you might as well replace all four of them....if ones bad, the other three will likely be that bad soon, if they aren't already.


Matt

[Lnzbug]

I had the same problem. John replaced all four ignition coils. It didn't completely solve my problem. He then changed the spark plugs & it's been great since. I had about 230k miles in him.

[MisterTurbonium]

New coils are in. Car still runs, so that's good I'm not going to say yet if it fixed the problem because it's a hot day and it's always been less present on hot days. I'll be back with an update when this weather passes.

One thing about the new coils: they're snap on, no bolts. VW must have updated them because the original's were bolted down. I put the bolts back in just because I don't know what else to do with them, but they won't go all the way down. Also, one bolt is missing from some time in the past, probably at the dealer. Any particular concerns about this?