01 Jetta revs when cold starting

It's done this since I've bought it and I'm not sure what would cause it. Only when it's cold, I start it and it'll quick rev to bout 1500 then idle back right away to high idle and run slightly rough for a second.

Could injectors be leaking when it's off and it's burning the fuel off or is it a pump problem. There's no codes or cel. Runs great otherwise, I guess it's not really a problem, just want to make sure there's nothing wrong.

Fuel shutoff solenoid is binding up, order a new one and replace it.

More than likely you may be getting intermittent loss of power as well.

$85 fix.

VW Part number: 028130135F
Bosch part number: 033001042

Do fix this sooner than later, it will eventually strand you.

Huh, hope it is that easy. Not a bit of power loss. It runs great, even with 215k on it. Thanks for the help

I have heard a faulty coolant temp sensor can cause similar symptoms.

Coolant sensor is new, it was causing a whole heap of problems. Really eneded up being the ECT sensor plug. Corrosion...

Disregard the other guys and change your solenoid....

The easiest way is to remove the pump top, you will of course need The security bit to do this.

You mentioned corrosion, so I suspect your motor is pretty clapped out from not washing off road grime and failed to keep things clean.

When you go to work on the pump, degrease and completely pressure wash that engine, the last thing you can afford is crap falling into that section of your pump... Immediate failure is an absolute possibility, cleanliness can not be over emphasized.

After cleaning the solenoid area, remove the pump head (top only not the middle base) if you want (I prefer this route since I can use a socket on the solenoid to break it free.

Note: if you don't remove the pumps top, You may be able to use a pipe wrench instead of removing the head, the solenoid is scrap anyway so who cares about the marks.

The solenoid will require between 120-150Nm to break free (dissimilar metal corrosion), remove the plunger/spring since it will have fallen off the solenoid.

When reinstalling it's straight forward, torque is 80Nm a box end wrench should do the trick.

Pump top screws are snug + 1/8 turn.

Well I've finally had time to look for the solenoid and it's not 85$. From the stealership it's 203$ and online it's 150$. Couldn't find the Bosch part with the number you gave me. You pretty sure this is the fix for that? I'd hate to drop 150 an not fix it.

On another note, would this also cause it to idle high when cold as well? I mean around 1000 after its revved and came back down.

You can keep guessing or follow my advise... Good luck to you.

It's as obvious to me as you walking in with a burned out light bulb, and then you questioning if it's really a burned out light bulb...to which I reply your right it's the blinker fluid.

Tongue in cheek, now go replace your solenoid and quit complaining about maintenance costs.

If you took it to the dealer they'd gouge you for an entire injection pump and hand you a $4000 bill.

I am curious. What is it that makes the engine race upon start up when the solenoid binds? It is either open or shut when it operates, isn't it?
I have read that this could also be just the solenoid's seal that is failing. Is this a fallacy?

The rev up is due to the start sequence of the TDI...

First, shutdown...

When you shut the engine off you de-energize two circuits, the fuel shutoff solenoid and then the control collar (this moves to zero fuel delivery, which is also the position used during over-run or when coasting in gear).

When you start the car, as the ignition key is moved to run the ECU commands the fuel shut-off solenoid to open, however the control collar is now also energizing and positioning from zero fuel delivery to the defaulted position that is also set by way of an IQ adjustment.

Background: lower IQ values result in faster starting since collar movement is less and faster initiation of fuel delivery results to the injectors. Conversely, higher IQ values take longer since the collar must move slightly further before actual delivery commences.

Regarding engine rev up on start...

The fuel shut-off solenoid when energized is not fully opening or in some cases closing. In this case the OP's solenoid is not opening fully or is binding up in the bore for whatever reason.

The ECU now commands IQ movement by way of the control collar, however since the port to the high pressure plunger is blocked, the ECU keeps commanding an increase in delivery quantity. After a few rotations the plunger lifts and now case pressure fuel is now allowed to enter the high pressure plunger bore and onward to the injectors after compression....

BUT...

Since the control collar was positioned higher due to no delivery as the engine fires the delivery rate is 2-3 times that required for stable RPMs and you get a brief rev up before the ECU can reposition the collar back to normal idle positioning.

If the plunger does not fully lift, you get a restriction of fuel entering the high pressure plunger bore. The effectively throttles the plungers fuel delivery and you get cavitation that reduces peak volume available from the pumps high pressure plunger bore.

The tricky part is since fuel us not measured for quantity (only crank acceleration is monitored), this issue will not trigger a fault code requiring a thorough working knowledge of the system to diagnose. The tell tale signs are obvious if you know what you are looking for.

Or just take the plunger out.

It is redundant for shut down on TDI's.

In a pinch... True!

You'd get a slow shut-down, but it would work.

Thanks for that.

Well I'm definitely not whining about parts cost, I have no trouble throwing a couple hundred at parts if I know that's the problem. Being as I'm new to this forum and don't know you from jack in the box, you should understand my questioning. Been on lots of forums and worked on lots of different vehicles and have got lots of bad info from people on said forums that don't know what they're talking about.

That said you most obviously DO know what yer talking about with an excellent in depth explanation of how the injection system works on these cars. I'm used to mechsnical pumps on old pickups and tractors. Thank you for the info and I will get one ordered.

Welp...didn't fix it. Still revs, still idles high for a bit, and still runs great.

Ima guess pump timing wouldn't cause that? Whoever worked on this car last wasn't qualified for the job, as the pump was off when I did the timing belt. As the pump lock tool wouldn't go in on tdc. Haven't had time to take it to a vcds yet.

Any other ideas?

Drivbiwire said:

You can keep guessing or follow my advise... Good luck to you.

It's as obvious to me as you walking in with a burned out light bulb, and then you questioning if it's really a burned out light bulb...to which I reply your right it's the blinker fluid.

Click to expand...

Kyleig said:

Welp...didn't fix it. Still revs, still idles high for a bit, and still runs great.

Click to expand...

well... this is awkward.

Ha, Just a bit...and exactly the reason why I questioned it. The car has all the same symptoms except loss of power and that doesn't mean it's the same problem as all the others.

That's why I suggested taking the plunger out. No money/parts replacing involved.

I take it your talking about the plunger on the bottom of the cut off? Everything looked good on the old one, o-ring and all. I think it just needs to be on a vcds with someone that knows how to run it. I don't have one but a guy not far from Me does but he hasn't used it enough to have the know how to utilize it. Good guy tho, said I can use it anytime I need to.

How much cranking does it take to have the engine fire off?

Was the CTS mentioned? I bring it up because your say that the issue is only when cold.

Would be nice to be able to log what's going on when this fires off. I'd think that one could better narrow it down.

DBW sure disappeared quick eh?? lol.

Kyleig said:

Welp...didn't fix it. Still revs, still idles high for a bit, and still runs great.

Ima guess pump timing wouldn't cause that? Whoever worked on this car last wasn't qualified for the job, as the pump was off when I did the timing belt. As the pump lock tool wouldn't go in on tdc. Haven't had time to take it to a vcds yet.

Any other ideas?

Click to expand...

- You inspected the Solenoid plunger bore to be sure there was nothing to cause the plunger to hang up.
- Solenoid was replaced using the new plunger the came with the solenoid.
- O-ring was replaced at the base of the Solenoid.

If you followed those items, The only other explanation would be the control Collar servo hanging up on the pump. Remove the case top, check for corrosion or varnish build up in the pump. You can feel for free range of motion of the servo without major disassembly.

It fires right off. No hard starting whatsoever. And CTS? What is that? Of course just as I tell everyone it's only when cold, it does it pretty regularly now. Always starts right off tho.

I did replace all parts with the solenoid. Everything you mentioned, and the bore did look good, everything was clean. Where can I get the special socket to remove the pump top?

My vcds will be here on Monday next week, I will need some direction in logging to see what it's doing on startup. I have only messed with one once and it was just for a minute.

I'm not entirely sure this is what fixed it, but I got my vcds yesterday, checked timing and at first it showed slightly advanced, adjusted, went to much..bumped it a little more the other way, and I mean I didn't even see it move then all of a sudden it was way off the chart advanced. 94 I think? Got it down just under the blue line and since I've done that it starts perfect. I didn't change anything else on it so I can't think it would be anything else.

I'm not thinking that a change in timing, especially if it fires right up to begin with, is going to make any difference with the revving issue. That you're not seeing it right now I think is coincidental. Keep us posted.

Oh, "CTS" = "Coolant Temperature Sensor" (was kind of a reach, but was thinking of stuff of temperature stuff that could trigger this issue; this also brings up the issue of the fuel temperature sensor- maybe an actual guru could chime in on that)

Oh gotcha, that sensor is new too. It caused me a whole heap of problems when I got that car.
I didn't think it would help but the only other thing I did was run the engine tests on vcds. I do wonder sbout the fuel temp sensor now bc I had trouble getting it to temperature. It does need a tstat I'll get that today.

The fuel temperature sensor is located inside the (top of the) IP. It is responsible for adjusting the fuel QA (I believe) to compensate for changing fuel temperatures. I believe that the ECU should store a code if the sensor is messed up.