Loud rumble/vibration on and off during idle

I bought a 2002 Jetta tdi with a junk auto trans and just swapped a manual trans, did the timing belt, cleaned the egr and turbo. It was setting at idle with the A/C on and all of a sudden a loud noise and heavy vibration came from the engine. RPM's did not change. After 5 secs it was gone. The sound/vibration almost sounds like a small air compressor tuning on in the engine. It happened again during this same drive, setting idling for maybe 2 minutes and the sound/vibration started then stopped 5 secs later. It shakes the steering wheel and everything.

I have had the car setting at idle for longer periods of time and this never happened. Before I put the new trans in and did the timing belt and everything. I had it idling and adjusting the IQ using the hammer mod and this noise/vibration also happened. On for 5 sec, then went away.

Anyone have any idea of what this could be? Like I said the noise is very noticeable and the vibration is very intense. It almost feels like the engine is redlining for 5 secs.... but I know that's not the case....

So I was able to capture the shudder on video, this was while I was setting in a drive thru with the A/C on and the shudder started to happen. Turn the volume all the way up, you will notice the difference when I turn the A/C off. When i turn the A/C back on though it doesnt do it.

Now i was setting in stop and go traffic because of a wreck and the shutter happened and would go away with the A/C off but when i turned the A/C on the shudder would come back....

This only happens at idle. Never while driving. And it has to be idling for a period of time before it does it. I know now it is directly related to the A/C I am just not sure what is happeneing....could the compressor be sticking/freezing up at idle while the rpms are low and then the belt is jumping/slipping??

Turn the volume all the way up
https://youtu.be/DWxhcv3d9dg

Did you use vcds? What's your IQ at? The compressor adds extra load to the engine, so if your IQ is too low, it could explain the vibration while it's engaged.

snakeye said:

Did you use vcds? What's your IQ at? The compressor adds extra load to the engine, so if your IQ is too low, it could explain the vibration while it's engaged.

Click to expand...

I do. But that wouldn't explain that It doesnt happen all the time. I just took the car out to warm it up and then let it set with the A/C on for 10+ min and it never did it.....

I have my IQ adjusted slightly high in the recommended range. I cant remember the number off the top of my head. Plus wouldnt the rpms change? The rpm does not change when the shudder is happeneing.

Now today I drove to get lunch and was setting in the drive thru for 5 minutes with the A/C on and 8t started to shudder. I turned it off and back on and everytime I turned it back on it would eventually start to shudder.... makes no sense.

After you did the auto to manual swap did you raise your Injection quality...... I bet it’s at about 1.5..... you need to set it with VCDS to about 4-5........
your getting too much fuel at idle.....

Usually you get slow down shudder on... Slow down. Not at a complete stop. But definitely a good idea to check the injection quantity. RPMs won't really change, but you'll feel it.

Does it ever do the shuddering when the AC is OFF?

Injection quantity was set after the swap. I'll check it again. And it has never done the shutter with the A/C off. And like I said o tried to repeat the same condition....A/C on and let it idle and it would never shudder....

So I got the car warmed up and got on vcds to look at the IQ. In the video I switch the A/C on and off multiple times. The last time i switched the A/C the car started vibrating and as you can see the IQ stays higher then the other times.

Idle - 4.4-4.6
Idle w/ A/C - 8.0 -8.2
Idle w/ A/C and shudder - 8.8 - 9.0

Anyone have any idea what this would be happening?

https://youtu.be/-rGnmBx7iFc

For what it’s worth .......
First give it several minutes between each cycle of your Comp switch and let it stabilize.
Second as it seems to only happen with the a/c on I would just for $hits and grins hook up a set of gauges and see what pressures you are producing.
Third don’t have a clue why your IQ goes up that high..... I would have thought it would go the other way when a load Is put on the engine, increase fueling........

FWIW, had a similar issue on an OLD Jetta. 1984 I think. Turned out to be nothing more than loose ac compressor mounting bolts. Check it out.

csstevej said:

For what it’s worth .......
First give it several minutes between each cycle of your Comp switch and let it stabilize.
Second as it seems to only happen with the a/c on I would just for $hits and grins hook up a set of gauges and see what pressures you are producing.
Third don’t have a clue why your IQ goes up that high..... I would have thought it would go the other way when a load Is put on the engine, increase fueling........

Click to expand...

For your first question, not sure why this would make a difference, I've had this happen while driving 100 miles with the a/c on then setting in traffic because of a wreck, shutter would start after a couple minutes of idle
Second, guages? What pressure?
Third. It is increasing fueling I thought???? That number is milligrams of fuel per stroke correct? High number = more fuel....?
Also I should add, the car doesnt run very well when cold and not in boost. If it sets for any amount of time that allows for the engine to get cold it blows white smoke at start up and runs rough. Once you take it on the road it comes out of it on boost, and in just a couple minutes it idles and runs smooth.

I used to have a cylinder 1 misfire code, before we did the trans swap, timing belt, and intake/egr clean. Also before all that I checked the compression and cylinder 1 was lower then all the others, it also took quite a few cranks to build pressure, both cold and hot on all cylinders. If I remember right cylinder 1 was 360 or 380 and the rest were around 420. Looking at the intake and egr and since the auto trans was junk I would say it wasnt run very hard at all and was hoping if I drove it hard for a while maybe it would help (read on here that the rings could be stuck or something from lugging the engine all the time).

I believe the rough idle at start up is cylinder 1 acting up, my best guess anyway. Once its warm it idles and runs perfectly fine.

Also I once parked the car uphill and it would not start, IP was completely empty, had the fill it of fuel for it to fire. So I was going to start replacing lines..... with that being said maybe alot of these issues, including the A/C shutter maybe has something to do with a air getting in the lines or a leak(havent noticed any leaks). IP not getting supplied with enough fuel at idle to keep up with A/C load?????

rocky raccoon said:

FWIW, had a similar issue on an OLD Jetta. 1984 I think. Turned out to be nothing more than loose ac compressor mounting bolts. Check it out.

Click to expand...

I can check. I would have thought we would have noticed this when we did the timing belt change. And I feel like that wouldn't explain why its intermittent.

Well I replaced all rubber fuel lines, the smaller return lines, and the tee on the fuel filter. Still got shudder. IQ was at 4.5 so I adjusted it in VCDS to 4.0 - 4.2 adding more fuel. Have to see if that helps.