Weird shifting, brakes, etc.

[ELO78]

2003 Weekender. Rebuilt trans 2 years ago.

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Here are the symptoms:

02/27 Tuesday afternoon, cold start
-Shift to D, unusual response from gas pedal, very slow acceleration
-Brakes much less power than usual, until running for a couple minutes
-During light or normal acceleration, trans shifting very unusual and very early compared to normal. Shifts aren't hard or harsh.
Drove 30 miles from work to home

02/28 Wednesday morning, cold start
-Shift to R, engine died
-Restarted, drove 1 mile, all the same symptoms as Tuesday afternoon

02/28 Wednesday afternoon, warm start
-Shift to D, drove 1 mile, all the same symptoms as Tuesday afternoon, except brakes
-Brakes felt normal

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I used VCDS -- here are the codes:

Tuesday evening
17704 - Error in Mapped Cooling System (check Temp-Sensor and Thermostat), P1296 - 35-10 - - Intermittent

Wednesday evening
01202 - Diagnostic Cable, 44-10 - Short Circuit - Intermittent

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Questions? Comments? Suggestions? Jokes?

Thanks!
_________________
Eric
1990 Westy Multivan, 2.1 L WBX, 4-speed - SOLD
2003 EuroVan Westy Weekender

[gesoffen]

Based on the symptoms alone, I would guess a vacuum leak and/or secondary air pump (SAP) issue. I'm guessing the vacuum leak due to the behavior of the brakes. However, the cold start stall could be vacuum leak or SAP.

While I'm not certain on this, the ECU likely uses a manifold air pressure (or similar) signal as an input for shift points. This would help to provide delayed up shifts/early downshifts when the engine is at high load/low vacuum.

That said, the code for the cooling system may be related - if the engine thinks it is warm/hot at cold start, it will use a different fuel map which could cause stalling, rough running and as a result an inability to make vacuum (hence the brake and shifting issue).

If it were me, I'd start with the troubleshooting the temp sensor. From there, do a good check over on the vacuum and SAP system.

Sorry for such speculative guidance....

[EuroTec]

Check for vacuum leaks first. Weak braking force is the clue here, also stalling when in gear and shifting too soon.
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If it ain't broke, don't fix it!

[jjvincent]

The plastic line to the check valve on the brake booster has a tendency to start to crack and split on the barbs. Thus it'll create a vacuum leak and thus you never get enough vacuum to the brake booster. Mine failed but I got one of the last new ones left. So pull that check valve and line out and inspect it. For a temp fix, you can use self bonding electrical tape (they sell it at hardware stores) ad then zip tie it on both ends.

If that's not the case, then do what others said.

[ELO78]

Thanks for these excellent suggestions. I'll let you know what we find...
_________________
Eric
1990 Westy Multivan, 2.1 L WBX, 4-speed - SOLD
2003 EuroVan Westy Weekender

[ELO78]

Welp, it took a while, but my mechanic got it all sorted out, plus some additional things.

Replaced the brake booster vacuum hose and valve.

Replaced the trans valve body, ribbon harness, and drum. This was covered under the trans rebuild warranty from 2022. Phew!

Adjusted the exhaust to get it up off the sway bar. I had a TT exhaust installed in 2022; it never lined up quite right.

Replaced the AC compressor. The pulley bearings were whining.

Replaced a torn axle boot. Likely torn when they lowered the trans. No charge.

Alignment.

The van drove great for the 56 miles from shop to home. So far, so good!
_________________
Eric
1990 Westy Multivan, 2.1 L WBX, 4-speed - SOLD
2003 EuroVan Westy Weekender