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Discussion Starter #1 (Edited)
Well, I've finally decided to post my issue. I hope it's in the right place on the Forum. I have a 2003 VW New Beetle 2.0 GL, 102,000 miles. (AEG on timing belt cover, but BDC per VIN number-just found that out today-lovely). Anyhoo, I have done a LOT of work on this car since I bought it in May. I'm going to list things I have done myself already. I have installed a new radiator, expansion tank, cooling fans, thermostat, radiator hoses, air filter, secondary air intake hose, hose from FPR to manifold, a couple of other cracked hoses, battery, alternator, alternator harness, fuse box, canister purge valve, shocks, brakes, rotors... SO, I finally drove myself berserk trying to figure out what was causing this bumbly, rough sporadic idle at low RPM (stop lights, parked, etc). I have no issues with hesitation, stalling, acceleration. It also has a mild gas odor from time to time. I finally took it to a MECHANIC. Very reputable and trained/certified (whatever) on German cars. My car is not throwing any codes. I let them replace the spark plugs and wires, but the rough idle persisted. They then had it for three days trying to diagnose this rough idle. They consulted with others. They did a smoke test (all good), along with inspecting hoses, other parts, etc. No answers. Everyone is baffled. They can feel it when seated in my driver's seat, but have no idea what is causing it. It is making me nuts. I have rolled around various fuel system issues. I have plans to get timing belt and water pump replaced, but before putting another dime into a mechanic (I dare not mess with timing belt), I want to figure out my idling issue. And I really don't want it to be my fuel injectors LOL...getting the manifold cover off is a PIA! Any help, suggestions, education is appreciated. I am not a mechanic. I'm just trying to avoid a pricey mechanic (my GOSH, EXPENSIVE), but I was desperate for an answer. Thank you in advance.
 

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Considering the vintage of the vehicle and mileage; you might try cleaning the throttle body, replace the gasket and run the throttle body alignment procedure with a vw specific scan tool, like VCDS by Ross Tech. This doesn't cost much and something you can do yourself; worth a shot, we have had many 2.0L owners with idle, dying, stalling issues, there were solved with a simple clean and tba.


Beyond that, I would be looking at live data and fuel trims, to see if there is a possible vacuum leak or maybe a fuel delivery problem.


If you had a ignition related issue; would would think, you will be seeing some misfire codes. What scan tool; are you using?

It sounds like you have looked at allot of the typical problems; one would look for and your mechanic as well, things like smoke testing, would seem to find any vacuum related leaks.

Give it a throttle body clean, throttle body alignment, a shot and check your fuel trims; we can go from there. Thanks. :)

PS: if you have the ability; to make a video with your phone and post it up here or link it on youtube, that would be one way, for us to observe the nature and severity of the idle issue.
 

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One other thing that comes to mind is the clutch. VW used a dual mass flywheel (DMF) on these cars in an attempt to make a smooth shifting quiet running setup, and were very successful at that.

However when the flywheel starts to separate that can cause some vibration issues, now you only have 100k on your car and these clutches were good till about 150k or so , my daughters beetle which I just put a new clutch in was at almost 200k. I throw that out as a possibility only, her car was shuddering on acceleration, not slipping, and was rattling occasionally, not all the time. I document it here.

 

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Discussion Starter #4
Considering the vintage of the vehicle and mileage; you might try cleaning the throttle body, replace the gasket and run the throttle body alignment procedure with a vw specific scan tool, like VCDS by Ross Tech. This doesn't cost much and something you can do yourself; worth a shot, we have had many 2.0L owners with idle, dying, stalling issues, there were solved with a simple clean and tba.


Beyond that, I would be looking at live data and fuel trims, to see if there is a possible vacuum leak or maybe a fuel delivery problem.


If you had a ignition related issue; would would think, you will be seeing some misfire codes. What scan tool; are you using?

It sounds like you have looked at allot of the typical problems; one would look for and your mechanic as well, things like smoke testing, would seem to find any vacuum related leaks.

Give it a throttle body clean, throttle body alignment, a shot and check your fuel trims; we can go from there. Thanks. :)

PS: if you have the ability; to make a video with your phone and post it up here or link it on youtube, that would be one way, for us to observe the nature and severity of the idle issue.
Hi Billy, thank you for your quick response. You're making me feel a little better already because I had dirty or failing throttle bottle in my mental queue. The VCDS will take some learning on my end before I attempt it. But that brings me to my engine code confusion. The pink sticker on the cover on my timing belt says "AEG", but by VIN it is a BDC. It seems that will make a difference in how I go about the TBA.

I am unsure of the scan tool they used, it was a computer type system that they had hooked up while it was running. Obviously something much better than my puny OBD. They did that several times over the course of the 3 days it was there. There were no codes at all.

If you can describe what type of video would be helpful, I can probably make it happen. The problem with that would be that I don't SEE anything moving when the idle bumps around with the hood up, and there are no random noises when it's "bumbling". I only call it that because other than microscopic changes to the RPM needle, it is mostly felt right under my butt when I'm parked or stopped at a light/stop sign. It's a soft intermittent, with no pattern-bump..bump bump..bump.........bumpety bump.....bump feeling, which I can't video LOL. Again, thank you so much!
 

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I can say that an '03 would definitely not be an AEG from the factory. I believe there should be a tab sticking off of the head that has the engine code on it. Though its possible that maybe there was a timing belt failure at some point and the head swapped out? Or engine all together? Can you take a picture of the engine bay?
 

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Discussion Starter #6
Thank you Smiley. There is no telling what this bug has seen. Carfax looked super the first 10 years, it looked ok the 4-5 years after, but had 3 final years of silence 👀 Anything could have happened! I’m just wondering if I can get at least 50k miles out of this booger. I’ve only put 1700 on it since May 2019. I’ve been working on it this entire time 😭
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That's definitely an AEG manifold. So either its had a head swap or the whole engine. The AEG ended in '01
 

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Another possibility on the "rough idle", not being able to see it moving in the engine compartment but "feeling" it in the seat... is worn engine and trans mounts. I 've seen a number of times; the "dogbone" mount, being particularly worn, have substantial play in it and causing something you are describing. This is a very common problem on the mark IV Volkswagens, especially with older vehicles with high mileage and so it is definitely worth checking out.

If this car has been hacked and have a installed engine, parts from other years, many other possibilities maybe a issue. While these cars have endless parts that can be installed on (physically fitting); it is not always clear, if they are typically fully compatible, say different years ecu's etc.
 

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If the engine/head has been swapped out I wonder if the cluster has also been swapped. It might prove informational to check the computer VIN and mileage against the VIN tag under the windshield and the cluster mileage.
 

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Many parts have the production date on them; so, you could check things like the ecu, etc. to see if they match the model year and around the production month, indicated on the sticker on the drivers side door sill. I guess you can do some detective work and figure out what's going on it looks like the engine has been swapped possibly?

The photo of the engine sticker, on the plastic timing belt cover; indicates rhe engine code and what I assume, is the production date of "17-05-99", date 17th day, month MAY, year of 1999. Feel free anyone to correct me but that's what it looks like to me?
 

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Discussion Starter #11
Thank you everyone! Unfortunately, all of the stickers that would be on this car are gone, or so worn they can’t be read. So if AEG was discontinued in 2001, then a swap must have happened. What a mess. Now I’m not sure which way to head with this. Keep it or sell it and be done. It runs great, just has that rough idle. It’s my only vehicle, I work from home, and most of my driving is within 5 miles from home. Lots to think about here.
 

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Discussion Starter #12
Many parts have the production date on them; so, you could check things like the ecu, etc. to see if they match the model year and around the production month, indicated on the sticker on the drivers side door sill. I guess you can do some detective work and figure out what's going on it looks like the engine has been swapped possibly?

The photo of the engine sticker, on the plastic timing belt cover; indicates rhe engine code and what I assume, is the production date of "17-05-99", date 17th day, month MAY, year of 1999. Feel free anyone to correct me but that's what it looks like to me?
I see the same date you see. May 5, 1999
 

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Discussion Starter #13
That's definitely an AEG manifold. So either its had a head swap or the whole engine. The AEG ended in '01
Smileybug, can I bother you to show me what my manifold should look like if it is in fact BDC per VIN? I’m seeing pictures but whooo-they look so different! This could also explain why I have several areas around the engine that look like something USED to be or should be there 😱
 

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Discussion Starter #15
BDC engine pulled but pretty good photos on this long block on ebay:

Oh wow. I’m going to hazard a guess that it was a total swap based on the images vs what I have seen while working on it. I’m going to poke around in it this weekend, and probably take more pictures, and look at the configurations side by side, to see if anything looks frankensteined, and if I can find any original parts with dates, etc. I’ll also try to catch video concerning the idle as well. You’ve all been so helpful, and I really appreciate it!
 

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Discussion Starter #16 (Edited)
I went ahead and videoed my gauge. The “bumping” I feel during this does not match up with RPM gauge, it is felt sporadically, but with frequent consistency. I’ll try to make one of the engine bay while it’s running this weekend at latest.

<iframe width="560" height="315" src="
" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
 

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Looks like the idle is pretty smooth. I would probably be looking at motor mounts. Since there has been some sort of swapping done, its hard to say if the mounts are original or not. Certainly would not be out of the question to have worn mounts on an '03. I replaced the dogbone and I believe passenger side mount on my '03 GTI a couple of years ago from wear.
 

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Discussion Starter #18
Looks like the idle is pretty smooth. I would probably be looking at motor mounts. Since there has been some sort of swapping done, its hard to say if the mounts are original or not. Certainly would not be out of the question to have worn mounts on an '03. I replaced the dogbone and I believe passenger side mount on my '03 GTI a couple of years ago from wear.
Thank you, I will put that on the list for this weekend. I also plan to check out the throttle body. I'm now wondering if it is throttle by cable since an engine swap is highly suspect. Either way, I'm sure it will be dirty. I'm also going to clean the MAF, just because that's easy enough. I'd feel ok with switching out the dogbone myself, but I don't think I can get it up high enough to do it. Only high enough to take a peek at it. Not so confident about the two mounts. In other news, I made a short trip this morning, and a new noise showed up. It was more of a suspension type sound. I could hear it with my driver's side window down. This bumbling "idle" has been going on for about 2 months, and now this -making me crazy! Thank you to everyone, again :)
P.S. Her name is Dragnasty, and she is sure nuff living up to her name! :ROFLMAO:
 

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Discussion Starter #20
That was absolutely terrifying.
Even if I had what was needed to support the engine underneath, I still fear I wouldn't be able to get the mounts/engine back in so perfectly.
But I have a question in relation to this. If bad, would they cause more of a vibration rather than the "misfire" type feeling I'm having?
 
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