ALH Surging Idle and Smoking

[dlu]

We have a 2002 Jetta Wagon with an ALH engine and an automatic transmission with about 270,000 miles on it. A while back the idle began to do a regular surge of about 50-100 RPM that was most pronounced on cold starts. The surge rate is about 1 Hz and it seems to be a drop in RPMs followed by an almost instant recovery. The surging starts about 5 or 10 seconds after startup, and it settles out above about 1500 RPM. Once the engine is warm it is gone or much less pronounced.

I think I see a bit of smoke at idle that wasn't there before, and driving behind the car there is some smoke at cruise too (and mileage seems down as well). Occasionally heavy acceleration (such as getting onto a freeway) will produce a truly impressive cloud of black smoke – something worthy of the smoke screen from 007's DB5. It is bad enough that I worry it could be a safety problem for following cars. But this doesn't happen every time.

Recent work on the car includes (all post onset of the surging idle problem):

• Replacing the EGR and cleaning the intake manifold. The EGR valve was leaking oil from the anti-shudder valve shaft and was setting codes. Carbon build up was significant but not record setting. No noticeable difference (other than fixing the codes) after doing this.
• Replacing timing belt and related parts – this was done to replace a leaking water pump). For a short while the idle problem seemed to be gone or at least significantly improved. When it returned, it seemed like it might be related to electrical loads, it seemed to happen with a significant load (AC, seat heaters, rear defroster, but not headlights). When I replaced the timing belt I also cleaned a significant (maybe a cup) of oil out of the intercooler.
• Replaced air filter. No effect.

I don't think oil consumption is too bad – less than a quart in 10,000 miles of LubriMoly Top Tec 4100 (5W-40, 505.01).

I'd been thinking that the smoking problem might be due to a stuck turbo vane actuator, but testing with a MityVac I see movement start as soon as I start to pull a vacuum and I get full stroke at about 18" of Hg. As best I can tell movement is smooth.

I'd appreciate any thoughts on whether or not the two problems are related and what my next troubleshooting steps should be. I have access to VCDS.

 

[joewilhite]

my 2000 tdi jetta did that here recently at 84 k and it wound up being a ecu.
look at your vag.com scanner fueling and see if their is any fluctuations. thats where i would start. {vcds}

 

[dlu]

look at your vag.com scanner fueling and see if there are any fluctuations. that's where i would start. {vcds}

Would I be looking at the injection quantity? Any idea how much fluctuation is normal?

 

[dlu]

Update - cleaning grounds may have helped

Thinking that the problem could be with the control signals between the ECU and the injection pump I started off by cleaning all of the grounds in the engine compartment. After putting things back together the engine runs without surging with all loads off (except the DRLs).

I let it idle for several minutes and there was no surging. Turned on all loads except for the A/C and still no surging. Then I turned on the A/C and got a bit of surging that went away when I turned it off. I tried again and it didn't surge. I'm happy, but puzzled.

For my next move I think I'll clean the ground in the air plenum by the ECU. For whatever it is worth the grounds didn't look too bad. The connections were all tight, but they weren't shiny any more. Before putting them back together I cleaned them all with DeOxIt and 180 grit sandpaper, then I reassembled with Never Seez (or something like it) and retorqued.

 

[dlu]

So, I think I've got it fixed. I changed the fuel filter (it had about 30,000 miles on it) and filled the filter with Lubri Moly Diesel Purge and also ran another can of Diesel purge through the system by pulling the feed and return lines from the fuel tank and connecting the filter to a bottle filled with Diesel Purge. Cleaned it right up –*idle stabilized, light exhaust haze went away, and I can't make black smoke any more.

I think all of the electrical stuff was chasing a red herring…

 

[AnotherPerson]

I have a light surge with the ac on. It isn't enough to move the tach needle but I have a seat belt mech vibration that I can tell its surging from.

 

[dlu]

Ok, this is getting stranger and stranger. After running two cans Diesel Purge through the engine (one can used to fill the fuel filter and a second one in a bottle that I substituted for the fuel tank) the engine was running great –*it felt strong and the idle was stable and it wasn't making the heavy black smoke I'd been seeing.

That lasted for maybe 10 miles, this morning with the engine cold it was back to its old tricks with a stumbling, surging idle and have smoke when the load is first increased. My partner noticed this when she went out this morning.

I drove the car about an hour after she got back and with the engine warm there was little surging in the idle, or smoking, but it did feel like the engine might not have been as responsive.

My current thoughts on this are that with about 10 miles of driving the Diesel Purge is probably pretty well flushed from the filter and the engine is running on regular diesel fuel again. This makes me think that the problem could be fuel related. The car has about 270,000 miles and is still on the original injectors and pump. I'm wondering if Diesel Purge is somehow lubricating injector or IP components that are causing the problem. Would running something like Standyne help?

Needless to say, I'm really puzzled by this…

 

[1975 Kombi]

Did you ever get a fix?

 

[Schlitzguzzler]

Did you ever get a fix?
__________________
Thanks Brett

X2
thanks Dan