Throttle issue at highway speed - does not want to slow down!

2004 T1N - Owned it for over ten years and driven 86,000 miles. Alternator replaced last week. Drove it home from repair shop on highway no problem. This morning driving on highway for the first time in six days - stepped on brake to exit ramp and van tried to fight slowing down. Surprised me - thought I had accidentally hit accelerator; but pushed on brake and it slowed down. At around 25 mph, it behaved normally and continued to do so until I parked it. Came back out and it would not come out of park - No warning lights on dash. I tricked it out of park with a pen and it drove fine. Went back on highway up to 65 mph and it did it again when I slowed down to exit. Very scary like it does not want to stop. This time I braked and downshifted. Once again at low speeds, drives normally like there is not a problem. Never encountered this before. Reminds me of an out of control diesel; but there is no warning lights or message for high oil and it behaves fine at non-highway speeds. Anyone encounter this before?

I suggest some serious analysis of the gas pedal for starters .

The gas pedal unit consist of three variable resistors inside the assembly with what amounts to sliding shoe setting the R or ohms value which in turn is interpreted by the PCM as a throttle setting.

Obviously over the life of the vehicle the first 1/4 to 1/3 of the gas pedal gets the most wear and any malfunction is likely to be in that range or when backing off the pedal to coast .

The second can be the cruise control if fitted. This must be ruled out as you can have an interaction cancelled out when applying the brakes.

As so often a scan tool in live data can"see" inputs/outputs to localize the problem. In a more traditional Fred Flintstones method when it it sticks if you can give the immediate areas around the pedal a swift whack with rubber hammer on the floor. Don't whack the pedal itself--refrain from that! The vibration /shock has the effect of jarring the sliding shoe when worn to return to a more normal position inside the pedal assy.

In many cases seen this is will dictate a new a pedal assy and at about $ 850 which is a wallet flush.
In these instances to be sure we tend to install a good used pedal for test purposes and comparisons whereupon the customer usually opts for the cheaper used pedal assy once the issue is located.
Hope that helps & all the best
Dennis

I haven't encountered it, but i can think of a few things to try (or look at/for):
(a) who did the work? I'd start by calling them (although it may be coincidental.. so many things are)

(b) the brake pedal switch has *two* sections: one tells the ECU (engine control unit) that you're braking, the other tells the tail lights.
They can get out-of-sync, and there's a simple Reset procedure:
(1) crawl into the pedal area
(2) press the brake pedal with your hand, and look for the "stalk" (rod) from the switch that follows the motion.
(3) with the pedal pressed, grab that stalk with your other hand and (gently) pull it all the way until it stops.
(4) release the pedal (gently).

(c) wiring damage (or simply a loose connector or "tugged wire" affecting the brakes or accelerator pedal
(the accelerator pedal is also a dual-component device: two coupled potentiometers ('volume control knobs') that have to agree for the ECU to believe them.
(d) after doing (b), if the symptom still happens, i'd next suspect that the new alternator may have an erratic output ... either overcharging or dragging the system voltage down.

If i recall correctly, stepping on the brake is supposed to *also* tell the ECU to not feed much fuel into the engine, which is why i hope the Reset procedure may fix it.
But i don't recall anyone describing your symptom before.

It could be a faulty brake pedal switch, which is a fairly simple repair/replacement.

--dick (a 2004 service docs are here: http://diysprinter.co.uk/reference/ ... specifically http://diysprinter.co.uk/reference/2004-VA-SM.pdf )
p.s. ... and i always defer to Dennis' analysis...

The gas pedal unit should be fed +5 volts. The pedal unit can go bad or it can be burned out.
I saw a sprinter that the ECU was feeding +12 volts to the pedal. This burned out the pedal variable resistor. The burned out pedal unit caused the van to run at top speed only to be stopped by the ignition key.
The solution for that sprinter was a new ECU.
So check the voltage at the pedal. If it is 5 volts, just replace the pedal. If it is 12 volts, you'll need a new ECU too.

Sounds like your brake switch or brake light housings are broken. You likely had your cruise control on. Because the cruise did not see the brake pedal being depressed, it continued to try and maintain the set speed. The lack of brake switch signal also means your park interlock will not release.

Midwestdrifter said:

Sounds like your brake switch or brake light housings are broken. You likely had your cruise control on. Because the cruise did not see the brake pedal being depressed, it continued to try and maintain the set speed. The lack of brake switch signal also means your park interlock will not release.

Click to expand...

Ditto.
FWIW.

vic

I really appreciate all the feedback. This site is incredible. You have given me a great checklist/to do list to pursue. The shop that did the alternator specializes in German vehicles (primarily Volkswagen); but they maintain quite a few Sprinters, too. Thanks again everyone.

By the way, I did have the cruise on. Always flip it on at highway speed and never use it otherwise; so I will start with that thread!

It's also possible that your old *failed* alternator did the initial damage to the ECU (if that's where the fault truly lies)

--dick

Midwestdrifter said:

Sounds like your brake switch or brake light housings are broken. You likely had your cruise control on. Because the cruise did not see the brake pedal being depressed, it continued to try and maintain the set speed. The lack of brake switch signal also means your park interlock will not release.

Click to expand...

You can easily test this theory. If you're in this situation, manually kill the cruise to see if the problem is solved.

So as I attempt to diagnose this problem further in the midst of working and other pressing matters, I have discovered and remembered the following.
First, In between driving my Sprinter home from the Alternator replacement, I had a burned out tail light. I replaced the bulb I believe on Sunday morning before the issue started.
Second, All the lights work; but I do not have brake lights.
I think this points to the brake switch or brake housing (which?). Could the replacement bulb be the problem. Could a wire have gotton pinched taking out and reinstalling the rear tail light housing to change the bulb?
Thanks again for all the help.

You sure you installed the right bulb? Is the brake fuse good?

lancgsvcmb said:

Could the replacement bulb be the problem. Could a wire have gotton pinched taking out and reinstalling the rear tail light housing to change the bulb?

Click to expand...

"Could"?

Yes. To both questions.

--dick

Today, I finally finished replacing the brake switch. Removing the old one and installing the new one was a challenge. My 17 year old daughter ended up connecting the wires. Anyway, it worked. Thanks for the help.