Alh Jetta runaway

So Saturday night my car idled for an hour or so before I left and I went to leave and got a half mile down the road and it started revving all the way then it stopped for a second and started again then shut down. It prolly only revved all the way each time for 10 to 15 seconds. Now it will not start. I haven’t messed with it yet but was gonna start with a compression test on Friday. The only thing done to it is egr delete. Anything else to check for I was gonna maybe pull the turbo if it has compression.

Do you have oil in the sump? Check the intercooler, turbo, and compression.

Is that a common thing to happen to the alh? Ive had it for about a year and have no problems. And yea I was gonna check compression and turbo for sure just won’t have time till Friday.

Not common, but not unheard of. Runaway is almost always caused by the turbo seal failure. The engine ingests oil, burns it causing high RPM and most often, internal damage. Never good.

Also I forgot to mention that I messed with the pedal when it revved the first tome and it stopped and I let go and it started revving again. Could it have something to do with the throttle pedal postion?

If you search on "runaway" you should find some great background reading, as this is a frequently-discussed topic.

The TL;DR at this point is generally to pull the glowplugs and rotate the engine to see if any oil is ejected. If so, pulling the intake hoses from the turbo and inspecting the turbo impeller is a good idea, as is a compression test and a OBD scan with a VW-specific scanner.

The engine will start even with a defective throttle positioner, so it's likely something more serious is going on.

Also a consideration: a defective throttle positioner would most likely set a "flashing glowplug light" malfunction warning and store an error code.

No not a throttle issue. Like Bobnoh says it is most likely a turbo seal leak. You might as well pull the head and oil pan if it will not start (or look for another engine). Runaways are never a good thing. Bent rods and or blown pistons are common. I had one do it only for a little and melted 2 pistons. It probably needs a turbo as well unless you see the intake side is dry.

And another one gone, and another one gone
Another one bites the dust
Hey, I'm gonna runaway on you
Another one bites the dust

Not trying to victim blame here, but idling/low-boost allows oil to push past the turbo seals (the turbo likes to be put under load). This can allow oil to pool in the intake piping and get sucked in to feed the engine. I am not saying that 1 hour of idling would necessarily cause a runaway, but constant, long-period idling cannot be good for one's chances of avoiding a runaway.

Yes. There are a few threads here showing specifically how the turbo will fail at an early age from long idle times. Has to do with it pressing against the journal bearing face vs when boosting it pulls out away from it.

Just wondering out loud if letting the thing idle for an hour (a nono) could have caused some temporary situation, not a turbo seal failure. Cause what you described generally results in major repair. Did you notice how high it revved?

If the turno was in good health I dont think it would cause enough to runaway like this. Now if it was having issues or you had a higher than normal oil psi at idle that could be a reason. I would pull the boot off the inlet and feel the turbo for end playmakers should be none to extremely little end to end. Side to side there should be some. But not enough to feel loose. Just a tiny bit side to side. Like a mm or less

I don't think a discrete period of long idle would be a problem.*
My turbo died at 122ish K, and I think that's because of my long habit of
"conservative" throttle/RPM use due to not understanding these cars for
my first several years. Years back, I would "hyper-mile" often, thinking I was
saving fuel by keeping the RPMs low. Now I know better!
*I recall IBW tell a story about how he had to go help his Son do some construction work,
but had to take a kitty cat with him. He idled a TDI for hours on end to keep the cat from
freezing (or was it baking?). Anyway, that car idled for a day-o-work. I bet the turbo
is still fine.

if it was the life of a kitty vs the life of a turbo / car, yea kitty wins.
our coon/tabby mix i literally picked up in the literal middle of a BUSY AF onramp to I-81 off maugans AVE just before PA border. tiny little ball of fur curled up, about 2 or 3 weeks old. now he is 1.5 years old, had a busted back leg (probably sprained) but his tip of his tail is bent, he is 100% fine though. and the point was ... i don't know... felt like sharing.

I am pushing almost 550,000 miles driving these TDI's for 15 years and my wifes car it just turning 200,000. We have idled hers plenty of times during those 200,000. I often idle the cars for about an hour in the winter in the morning so I can stay warm while waiting for work to start. The only trouble I have seen in turbo problems is from cars I have purchased with bad turbos or from turbos that sat a long time and caused the vanes to stick. I heard all this stuff about idling is bad for these cars years ago but, too bad, I don't like freezing and I like driving the TDI's. My present car I am driving had just the cartridge installed at 120,000 when I got it. The previous owner blew the turbo. I now have 240,000 on it and that tells me turbo failure is more do to with other factors like wrong oil or driving habits. Don't drive hard from low RPMs, Don't drive hard from cold starts, and then drive them hard once in a while. (and don't drive if something is wrong).
Was your car smoking much when it ran? I had a parts car start running away after it was idling but it was smoking a lot. 15 seconds is too long for a run away and damage happens quick.
Having a run away can be discouraging but rebuild the car and if you do things right they will last for years.

The engine will not start... does it turn over easily like it wants to start? It would be a good idea to check for oil in the inter cooler but a non-complete runaway should not prevent the car from starting.

Well I did a compression test on the car
Cyl 1=120
Cyl 2=380
Cyl 3=450
Cyl 4=410
I think number one hole is a tad bit low lol. Next is tearing the head off to see anything. I now have a parts car most likely

Yep. Definatly bent a rod or worse
Engine is trashed. Pull the head off. Then the oil pan and see of it can be rebuilt otherwise it's going to the scrapper. Sorry. 120 is crazy low like not even close to working pressure. Leakdown test and oiling the rings then compression test again will lead to more info but based on what happened, you got a slug of oil in too fast and bent the rod. Really sorry for your loss

It is a bummer to have this happen. The one I had do a full run away just melted the piston and I was able to repair with a used pistons fairly easy. If you need something let me know I have a pile of internal parts and a complete good running engine if needed. There may be other options closer to you if the rest of the car is worth rebuilding. If the body is good I would repair the car.

If your willing to do the work and you get used parts like tgray had for you. The rebuild is not that big a deal. Just a long weekend of work and a few hundred bucks in parts. Remeber those bolts on the inside of the engine are 1 time use. Head gasket and timing belt job with a conrod and you should be good to go. Maybe

With all the help and documents on this forum it will keep you on track doing the job correctly.

Can't the low pressure in cyl #1 be due to a slightly bent valve not sealing?

Only a leak down test will show why.

Usually broken timing belts bend valves and maybe rods and runaways melt pistons and/or bend rods. The problem is the super high compression from the extra oil in the chamber creates too much heat and the piston can't handle both at once. It would not take much to drain the oil and pour in something like diesel in the glow plug hole. I can just about guarantee it will run out the bottom end pretty quick. Whatever the case the head has to come off if compression is that bad and you will see what happened. If a head gasket was blown then you would find 2 pistons right next to each other with low compression. It doesn't take long to pull the head. Just a little longer to put it all back correctly.

If you don't have a good way to do a leak down test and really want to know another way - you can take an air nozzle with a rubber tip placed into the glow plug hole and pull the trigger with the oil cap off (with piston on compression stroke). Put a wire down to find top dead center, and then if it pushes out the valves then roll it around 360. You will most likely hear the air rushing through the crankcase on the bad one and the others will try to spin the engine.