rough idle problem

Hello all,

I have a 2000 Jetta TDI. Lately I have been noticing a problem where the car seems to be having some idling problems.

Basically, the car normally idles at 800 or 900 RPM. In the past few weeks, it has happened to me 3 times that the idle RPMs are slightly higher, at about 1000-1100. While this is happening, if the car is in neutral and I give it some gas then let off the pedal, the RPMs drop at a normal rate until about 1300 RPM, then drop very slowly down to the higher 1000-1100. Then, if I sit there at this higher idle speed, the car bucks a bit, and the RPMs jump a bit then fall, about every 1-2 seconds or so.

This does not happen all the time, and as I said, has only happened a few times in the past week. At all other times the car is fine. Also, every time this has happened the car has been completely warmed up.

Finally, I did have the timing belt replaced but that was about 12,000 miles ago and haven't had any problems until recently.

Any ideas?

thanks,
matt

how many miles on this beast?

112,000

what's the condition of the intake manifold? How is the fuel quality where you live?

Very good questions

I don't know the condition of the intake manifold. I had problems with it getting clogged in the past, and experienced a serious loss of power. Power levels are fine now, actually, the car is driving great. Does that rule out the intake manifold? Also, is there any way to check the condition of it without removing it?

As for fuel quality, I'm not sure about that either. I'm in the Washington DC area, and typically fuel at either a citgo station or a texaco.

how long ago was it cleaned?

You can remove a large diameter rubber hose that feeds the EGR valve and have a peak inside. I'd do that.

It was cleaned at about 55,000 miles, so it's been about that long again. And, I've never done the fix that I saw listed in the FAQ. Hmm.. interesting.

As for the hose, you're talking about the big one that runs from the intercooler up to the EGR? If I take that off I'm looking into the EGR valve yeah? I guess from there you can see through that into the intake manifold? So, how much gunk is too much gunk?

If you have serious blockage, it's been known to cause poor idle quality and lots of other problems. Do you see unusual amounts of smoke when you accelerate from a stop?


who did the TB replacement? Has your fuel economy been normal since?

I see almost no smoke when accelerating from a stop. You'd expect black smoke? I guess too much fuel and not enough air if the intake's clogged?

The TB replacement was done by a place called lightning automotive in new jersey, a place I was recommended by some people from this site. Fuel economy has been the same as it's always been.

well, Lightning is supposed to be good so hopefully it's not related to the TB or clogged IM.

I hope you are not having issues with your injection pump. Has the CEL come on? Can you have someone local scan the car with VAGCOM to see if there are any clues?

No CEL. I'm guessing a VAGCOM won't tell me much in that case?

Why would the status of the IM have anything to do with the TB replacement at Lightning?

Keep in mind that DTCs don't always trigger the MIL.

The IM clogging is not related to Lightning...I was indicating that if you're relatively smoke-free, the IM is likely not the issue.

Do you know someone with VAGCOM?

Don't know anyone right now, but I'm guessing they're out there. You know anyone in the DC area, or MD, or northern VA?

What's a DTC?

Don't know anyone right now, but I'm guessing they're out there. You know anyone in the DC area, or MD, or northern VA?

What's a DTC?

Click to expand...

Have you had your brake switch replaced? Pressing the brake and the gas at the same time will cause your idle to rise to 1100.

If the brake switch is failing "on" you will get the symptoms you describe.

moondawg

DTC = diagnostic trouble code

There was a recall on the brake switch in the past year yeah? If so, then yes, it's been replaced, but I thought that only really had to do with the brake lights, I didn't know it could affect things like idling.

My problem is definately intermittent though, so I can't believe the switch is failing "on". Perhaps the switch is faulty and is failing sometimes? That sound reasonable? You know how I could check the switch?

Also, and this is maybe unrelated, and maybe deserves another post, but I just noticed today that when this problem happens, if I turn the car off, then turn it back on, the glow plug light stays on for a LONG time, even though the car is warm. Then, when I started the car, the RPMs jumped considerably. I don't know right now that these two problems are actually correlated, as this is the first time i've seen the glow plug issue, and it just happened to be at the same time i was having the other problem. By the time I got my car home, though, all was fine.

I have the exact same symptamatic problems as you. I feel your pain i have done everything i know how to do. I removed the
the EGR valve it was relativly clean i've done the EGR block off a few months ago. My injection timing has been off forawhile and i get excessive smoke for the first 15 min of driving. I was told that my CAT may be restricted from the excessive fuel burning in the exhaust.? I am having it CAT removed (i only drive off road) anyway i still have my idling problems "very, very annoying" surging

Also, and this is maybe unrelated, and maybe deserves another post, but I just noticed today that when this problem happens, if I turn the car off, then turn it back on, the glow plug light stays on for a LONG time, even though the car is warm. Then, when I started the car, the RPMs jumped considerably. I don't know right now that these two problems are actually correlated, as this is the first time i've seen the glow plug issue, and it just happened to be at the same time i was having the other problem. By the time I got my car home, though, all was fine.

Click to expand...

we have a winner!!!! Your coolant temperature sensor is bad. There should be a recall on this, but because it's not saftey related, there won't be.

Do a search for coolant temperature sensor, which will produce threads on how to replace it. It's a 15 minute job, albeit a little messy.

If you get your car scanned for codes, you'll get one about the coolant sensor.

moondawg