Cruise control won't hold speed....MY FAULT?!?

Hey Guys. First, I just wanted to say that this forum is extremely helpful! Thanks in advance for the help.

I have used the search and done a lot of reading on cruise control issues. None seem to solve my problem...

The cruise control won't hold the set speed. It definitely works and applies throttle, but not quite enough to keep the car at speed, and the speed gets slower and slower gradually. You can feel it engage and it will hold speed for a minute or so, and the decceleration is very gradual. This is a new problem, the cruise has worked perfectly in the past.

I have disconnected the MAF and drove for a bit, and this is definitely not the problem, there is no power with it unplugged, and lots with it plugged in. Maybe a sign of a soon to fail MAF?

The car pulls well and fuel economy is still excellent, no black smoke, really no performance change whatsoever.

Car: 2004 Jetta TDI PD. 110,xxx KM. Since last using the cruise for alot of highway miles, I have added studded tires, a rocket box and the foam pipe insulation grill blocker mod to reach and keep operating temperature in the cold. Would these mods have anything to do with it?? I don't see how these could effect the cruise. When you step on the gas there is plenty of power at highway speed.

What do you think?

Thanks again for reading and giving your input!

Cam

I have never heard about this problem on a modern VW. Very interested in seeing how this turns out.

Aside from the coast switch being flakey, I'm out of ideas.

Jetta TDI Cruise Control Problem

Camster88: I bumped into your post from May of last year regarding cruise control not holding speed. I'm having exactly the same problem with an '04 Jetta TDI. Up until the last few months, the cruise control was the best I've had in any car; always holding speed right on the money.

Did you ever resolve your cruise control problem? If so, I'd love to hear what you learned. My dealer replaced the crank speed sensor (it showed a "code"), but it didn't help. The wheel speed sensors show no faults. They say the only other option is to replace the computer, which seems a tad extreme (and very expensive).

hey DanVito. I just posted this thread today. From my research, it seems that this problem has happened the most on 2004 models? Bizarre... Hoping for a tdi guru to show me the way!

Ever figure this one out?

So there are several of you - all 2004 owners - with this problem? Bizarre!

Have you guys done auto-scans with VCDS to check for fault codes in all modules?

Any results? I'm trying to diagnose a customer's car and it's having the same issue!!!

I realize that it's not an ALH, but in my ALH I had an issue whereby I'd lose speed on any slight incline. This was shortly after I'd gotten my car, though initially it had worked fine. After cleaning my intake I no longer had this problem.

I suspect that the ECU might be seeing that increased fueling demands aren't resulting in maintaining the set speed (in my case the clogged intake was restricting performance enough to affect the CC), so rather than keep jacking up fuel it just kind of lets it go. Might be interesting to run some logs.

Logging with the VCDS may reveal more info.

I want to guess that if it is not a performance issue, could be an intermittent in the wiring from one of the cruise control switches to the computer,

Try a new MAF. A MAF sensor that's starting to die will often give this symptom as an early sign of a fading MAF.

Good luck.

Mine did this exact issue and a new 02 sensor fixed the problem. The bad 02 was causing the EGR to go wonky which messed with the cruise. You can test by unplugging the EGR and try it. You will get a CEL but see if the problem goes away.

Same issue here after major repairs

I have 2005 BEW wagon, 237K on the clock, with a cruise control that worked perfectly.
I took the car in for a new clutch (working well but making lots of noise), a preemptive turbo replacement (orig. turbo), and a new cam (lobes about gone). In the process, the glow plug harness was replaced due to it being like fried spaghetti.
When I got the car back, it runs great, but now the cruise control won't hold speed. I set the speed and it slowly decelerates. If I stab the gas pedal, it will re-engage and get back to the set speed, then start to decelerate again. Sometimes it will catch itself and re-engage to the set speed, but decelerate again. On one or two occasions it has worked properly.
Prior to all of the repair work, it was perfect.
Having read all of the threads on this issue, it seems that there could be a myriad of causes. My question is, which one of them could be causing this issue that would have been as a result of having the engine/trans out of the car for a couple of days?
Any help would be greatly appreciated.

Does the brake light switch have anything to do with the cruise control?

Me 2

I recently started having a similar problem with our '06 Jetta. At first. I thought it was the anemic acceleration issue caused by a clogged fuel filter problem from previous experience. I replaced the filter and drove it with no issues during the day. Unfortunately, the problem resurfaced when I headed home from work last night. At that point after a few miles of no cruise control and no respectable acceleration, I stopped, killed it, removed and reinserted the key and restarted. The problem resolved itself. Now I'm waiting to see if it comes back.

^^^^^^^^^^ looks like your problem is turbo limp mode because it fixed itself by restarting the car...

Still having the same problem, though I have narrowed it to grades

My problem is still persisting, though I have come to understand that it is only happening on uphill grades, even slight ones. On level ground or downhill grades it works normally, but any uphill grades and it loses 7-10MPH and then will catch itself (most of the time) and get back up to speed, but it happens over and over. Not too good for mileage or traffic behind me.

I haven't gotten any responses to my post so I guess I will just start replacing stuff and see what happens.

Limp mode == reduced power == will do exactly what you are seeing . . . scan it, don't just shotgun unneccesary parts!

- Tim

jdg- Your issue sounds like the MAF failure. Try it unplugged, clean and inspect the connector first.

JB05 said:

Does the brake light switch have anything to do with the cruise control?

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Yes. However a bum brake light or clutch switch will cause the CC to not even set. If the set speed is bleeding off, the CC did set and something else is the problem.

Like others have said, some work with VCDS is in order.

Thanks so much for the input I'll try having the guy that did the work scan it for me and go from there.

Carlos_TJ said:

^^^^^^^^^^ looks like your problem is turbo limp mode because it fixed itself by restarting the car...

Click to expand...

shouldn't I be looking for what caused the limp mode to begin with and correct that though?

jdg said:

My problem is still persisting, though I have come to understand that it is only happening on uphill grades, even slight ones. On level ground or downhill grades it works normally, but any uphill grades and it loses 7-10MPH and then will catch itself (most of the time) and get back up to speed, but it happens over and over. Not too good for mileage or traffic behind me.

I haven't gotten any responses to my post so I guess I will just start replacing stuff and see what happens.

Click to expand...

I already told you how to troubleshoot. Disconnect the EGR and see if if the problem goes away. If so, its likely either a stuck EGR or bad 02. VCDS would really help here.

When my car was doing this it turned out to be the N75 valve, there was debris interfering with the diaphragm, so the vacuum was not consistent to the turbo...usually happened while climbing hills.

What exactly led you to the N75 valve?

I checked the vacuum first, it was good, by chance I blew and sucked into the N75 and it would not hold vacuum and would go right through, pulled themetal collar off to have a look and there were little bits of rust IIRC, cleaned it up, reinstalled and everything worked correctly after that....and this was all after I had ordered the 17/22 because I thought the turbo was shot....

I know this is an old tread.
I have the exact same issue on two 2004 cars.
2004 Jetta TDI wagon Manual 0.658 5th gear
2004 Beetle TDI DSG
2005 Jetta TDI Sedan Automatic
2005 Beetle TDI DSG
Both of the 2004's have the cruise control losing speed on hill issue and both of the 2005's are fine.
The 2004 wagon manual (My daily driver) has loads of power, but loses speed on any incline. I do get occasional MAF errors on scans, I clear them and they seem to stay gone for a few days, then I see errors again.

16486 - Mass Air Flow Sensor (G70) P0102 - 000 - Signal too Low
I do notice the 2004 Beetle will not start or run without the MAF attached.
Both 2005's don't seem to need the MAF to run, I assume there was a program change to the ECU in 2005 that doesn't require the MAF?


Planning on heading to a wrecking yard to get a couple MAFs and PCV valves to try swapping things around to see if it fixes the cruise issue, if it does, I'll buy new parts.