01 beetle 1.8T rough idle, hard break pedal

[Capt.Huey]

My wife stopped in town to grab some lunch before heading to a meeting. When she got back in the car and started it, the rpms started surging and dropping off erratically. She drove a few hundred feet, tried to slow down for a stop sign, and the break pedal was really hard, and she had problems slowing down. Somewhere in that time the CEL flashed a few times then went off.

It sounded like a vacuum issues to me, so we had it taken to the shop. Got off the phone them and was told that they couldn't find a vacuum leak via 'smoke test' so they went through the engine codes and got back info about low voltage (which they ruled out), and a throttle body issue. He gave me a hefty quote if the throttle body needs to be replaced.

Just curious as to what anyone's thoughts are about the issue, car is an 01 vw beetle 1.8T manual with ~96K on it.

Thanks!

[Bluestream]

Could be your brake booster. See if it holds vaccuum...

[Boost Master D]

brake booster was my first thought.But then again Ive been known to be wrong and the beetle is a great car to do that!!

[IndyTom]

Originally Posted by Capt.Huey

My wife stopped in town to grab some lunch before heading to a meeting. When she got back in the car and started it, the rpms started surging and dropping off erratically. She drove a few hundred feet, tried to slow down for a stop sign, and the break pedal was really hard, and she had problems slowing down. Somewhere in that time the CEL flashed a few times then went off.

It sounded like a vacuum issues to me, so we had it taken to the shop. Got off the phone them and was told that they couldn't find a vacuum leak via 'smoke test' so they went through the engine codes and got back info about low voltage (which they ruled out), and a throttle body issue. He gave me a hefty quote if the throttle body needs to be replaced.

Just curious as to what anyone's thoughts are about the issue, car is an 01 vw beetle 1.8T manual with ~96K on it.

Thanks!

Don't have them replace the Throttle body. It can easily be cleaned. Those guys are idiots.

Tell me more about your symptoms. Did the RPM's surge while she was in gear and driving? Do a little test for me. Take the car on a road less traveled and accelerate to about 30mph. Then shift into 4th gear and floor the accelerator. If the RPMs go up but your car doesn't accelerate than your clutch is slipping. It usually first happens in the upper gears and then when it gets worse it will affect the lower gears as well. If that isn't it it could be the clutch slave cylinder. It has been known to fail and since the brake and the clutch fluid are pretty much intertwined on the New Beetle if can affect the braking performance as well.
Also if you haven't done so already check the fluid level in your Brake cylinder reservoir.

[Boost Master D]

I think IndyTom gives some good advice.

[TechnoTrix'd]

Did you have them check the main vacuum connection to the brake master cylinder?

That sounds like the culprit.

It a hard hose connection and if the plastic cracks it will void the vacuum but not allow a lot of smoke to pass.

That would be my first place to look.


Sent from my Autoguide iPhone app

[Capt.Huey]

Thanks for all the input guys!

Here's a bit of an update. Shop did a smoke test to try and find a vacuum leak, which came back completely negative. They next cleaned the throttle body, and reset the codes (although the CEL only flashed, and didn't stay on). I can get the codes, but don't have them now, but they were for the TB, low voltage, then cylinder miss fire - in that order.

After a day and half of further testing and driving the shop could not get the problem to re-surface. We have driven it a few times since picking it up and it seems to be fine.

The mechanic told me the amount of dirt in the throttle body he found usually isn't enough to cause an issue.

That being said I'm in the process of finding a new place to take it if the issue comes back, which I was told is a possibility.

Indy Tom:

The problem happened upon a warm start. My wife said it first felt like a dead battery, she tried again, held the key for a tad longer and got it to start, and then the surging RPMS roughly bouncing back between 800 -2000. She wanted to get off the main street so she went to the next intersection and while trying to slow down for the stop sign noticed the hard brake pedal. She proceeded to park it and shut it off. When I got there I noticed a little harder then normal start. and once running the same RPM surging she noticed. Because of the brakes, I didn't feel like driving it across town to the shop and had it towed there.

Thinking about it now, if it was indeed a vacuum leak, cleaning the throttle body shouldn't have made a difference, so i suppose I can rule that out, same goes for a bad brake booster? Am I way off here?

She drove it to work this am, no issues, thankfully it's a small not traveled back road. I would guess that if the symptoms were to pop up, it would be while starting it, since that's when the first occurred.

[IndyTom]

If it has trouble starting and it isn't the battery then the culprit could very well be the crankshaft position sensor. They do go bad and are difficult to trace.
Other symptoms are stalling when coming to a stop and unable to restart car.
Replacement REPA311803 Crankshaft Position Sensor | Auto Parts Warehouse

[Capt.Huey]

Thanks Indy Tom,

If the CPS is gone, then the problem would occur on each start right? If it is going bad, then they symptoms would be intermittent? A think I remember reading a bad CPS doesn't always throw a code.

I don't know about the stalling when coming to a stop, honestly when I started when the problem first occurred, it felt like it would stall each time the RPMs dropped.

Here's a list of the codes on the paperwork from the shop:

P1564 - when I looked it up, this is what I got "Idle Speed Control Throttle Position Low Voltage During Adaption"

P0300 - I think it's a general miss fire code
p0301 cylinder 1 miss fire
p0302 cylinder 2 miss fire

[IndyTom]

Originally Posted by Capt.Huey

Thanks Indy Tom,

If the CPS is gone, then the problem would occur on each start right? If it is going bad, then they symptoms would be intermittent? A think I remember reading a bad CPS doesn't always throw a code.

I don't know about the stalling when coming to a stop, honestly when I started when the problem first occurred, it felt like it would stall each time the RPMs dropped.

Here's a list of the codes on the paperwork from the shop:

P1564 - when I looked it up, this is what I got "Idle Speed Control Throttle Position Low Voltage During Adaption"

P0300 - I think it's a general miss fire code
p0301 cylinder 1 miss fire
p0302 cylinder 2 miss fire

"Idle Speed Control Throttle Position Low Voltage During Adaption"

That error usually means that the battery didn't supply enough voltage during the Throttle body adaption process and it more than likely failed to adapt. Ross Tech advises to put a battery charger on the battery during the Throttle body adaption process in order to properly finish and complete the Throttle body adaption.

Do you have access to a VAG com? Or do you know anyone with a Vag com in your area? It would be easy enough to do an adaption and see if that would help your issue.

Also check the voltage from the battery with the car off. It should be around 12.50 volts. With the car running it should be between 13.2 and 14.2 volts.
Make sure the connections from the battery to the alternater are solid and not compromised in some way.

[Capt.Huey]

Don't have a vag com, don't think anyone I know has one either. I have a battery charger that I use on my boat, but I', fairly certain it doesn't give out voltage readings, it just has colored LEDs. I will check out the battery connections, but I would hope the shop it was at would have done that. They supposedly check out the voltage and saw nothing wrong, but I will do what I can to double check it.

Is there a way to manually do a TBA, ie without a vag com or scan tool

[Smileybug]

All you need is a simple mutlimeter to check for the voltage. Something you should have if you plan on troubleshooting and doing DIY on your car for sure.

Where are you located? Plenty of people do have VAG-COM and can help you out.

[D2Beetle]

The Vag-COM (VCDS) Locator Thread is here ... not certain on how up to date it is.

[IndyTom]

Originally Posted by Capt.Huey

Is there a way to manually do a TBA, ie without a vag com or scan tool

There are a lot of people that tried disconnecting the battery for 15 minutes, touching the wires together to reset the ECM, then reconnecting the battery, putting the key in the ignition and turning it on but not starting the car. Waiting for 30 seconds and then start the car. Personally, I don't think that will work. It does reset the ECM but it really doesn't align/adapt your Throttle Body.
The only known working method is via VCDS/Vag Com software.

[D2Beetle]

Originally Posted by IndyTom

There are a lot of people that tried disconnecting the battery for 15 minutes, touching the wires together to reset the ECM, then reconnecting the battery, putting the key in the ignition and turning it on but not starting the car. Waiting for 30 seconds and then start the car. Personally, I don't think that will work. It does reset the ECM but it really doesn't align/adapt your Throttle Body.
The only known working method is via VCDS/Vag Com software.

x2 ...

Throttle Body Adaption is all to easy with VCDS; using the software, got to the Adaption Section, turn key on without starting and press the gas pedal down to the floor, then let it up and VCDS will display "OK" or "FAIL" on screen.

My skeptical .02 ... How would the ECM know that you are doing a throttle adaption without the right diagnostic tools? This is what VCDS does; it informs the ECM to perform the diagnostic procedure.

I am not certain if these "home grown" procedures actually do reset the ECM back to its original default settings; more like confuse it, thereby forcing a system wide re-adaption.