Hesitation Blues - FIXED!!

[Syncronoid]

90' Syncro Westy w/2.5L GW.

Van was sitting for approx. 3wks, before that ran fine. Now, even after up to running temp, engine is extremely slugging off the line. First time I noticed it was that first day after 3wks.... I was at a stop light to get on the freeway....slammed down the gas pedal and she almost stalled. Now, ~80% of the time, pressing throttle gently or firmly, it's still slow to rev up. Once it gets up to speed and on the highway it's fine, but when the RPM's drop, like taking an exit and wanting to accelerate quickly, it's sluggish again.

Rotor, Cap, Plugs, Wires, Fuel Filter were replaced just under 10k miles ago. New fuel injectors (new, from GoWesty), refurbished ICV and new O2 sensor were installed 775 miles ago to address failing smog (I passed after I replaced the injectors). Oil/filter changed more often than required. TPS clicks as it should when actuated.

All the above I do myself. Looking for input b4 taking to Peninsula Automotive in Campbell, CA (now that my beloved VanCafe is gone).

TIA
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'90 Syncro Westy w/GW2.5L

[E1]

Clogged catalytic?

Ours did what seems the same thing in Spring. Like it was getting no fuel intake or like the CPU or electricals went south, classic "Whaaa" sound under full throttle... and sporadically, dead-slow to accelerate. I ordered a new converter ten minutes later.

Though hard to hear the exhaust had a slight rattle to it, sounding like a bolt and nut were really loose.

I've surely been fooled by wind noise in our vans masking what's up out back. "Slower" is tough to tell from "slow" sometimes, and once up to "speed" things can all seem quite good.

Our issue cleared up over about 20-40 full-tilt highway miles. Our catalytic had apparently been clogged, or clogging over months of running rich while trying to diagnosis bad injectors.

When I pulled the converter off it was dead empty inside, leaving me to think the running condition was the last chunks of converter innards constipating the exhaust or the muffler -- as it were.

The rumors of running rich leading to converter failure are apparently correct.

Edit: And Oh, we also passed smog while chasing the injector issue. The converter condition then, unknown -- but only four months into what turned out to be 16 months of life, driving consistent monthly miles. Assume converter was still okay.

We only passed CO by about 10% when running rich. We have the GW injectors, too and they've been fine over 22 months now. I believe you can pop the plug on the converter to see if it runs better with less back pressure as a test.
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‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[Inlet]

Have you checked for vacuum leaks?

[Syncronoid]

Where does one begin to look/check for vacuum leaks??

[E1]

All the small hose lines cirumventing the engine. We replaced all of ours chasing a non-related issue and was shocked at how bad they were.

The one t-connector at engine center against the firewall is notorious for swaying side-to-side and pulling loose.
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‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[Syncronoid]

I'm not seeing anything loose or disconnected in any of the obvious lines. No cracks or holes in the air intake boot either.

[Inlet]

I never saw any of my vacuum leaks either... A lot of people won't like this technique but use starting fluid and spray it around all the vacuum lines, intake boot, intake plenum boots, do this while the engine running and is cool, if you notice any changes to the idle, you found a leak...have a fire extinguisher nearby too, as the fluid can ignite, although its never happened to me.

Another thing you can try is unplug the o2 sensor and go for a drive, any difference?

[Syncronoid]

Lighter fluid? No thanks! What does unplugging the O2 sensor do?

[E1]

[E1]

Inlet's suggestion is actually known and valid.

Cold engine, spray short and quick before warmed up, Kid gloves but not for the kids.

Unplugging the O2 discounts it from (potentially) sending bad air readings to mix fuel with via the ECU. If the engine's warmed up and runs exactly the same with or without the O2, I *think* that means it's toasted (open for verification here).

We replaced our last one with the $80-something Bosch instead of the prior $18 ones. I think it was worth it as we'd been through a couple cheap ones already and our mpg seems better on average now.

Dunno about your year, but our bus gives off a O2 warning light every 30,000 miles regardless of it still working.

Sudden bad running always brings up O2 and Temp II sensors as a quick fix.
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‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[Syncronoid]

Not doubting that's valid, I would leave that up to a shop to try.

[E1]

Fair enough... we did, too but it looked safe enough.

(and found a leak in a manifold hose, immediate rpm rev)
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[Syncronoid]

O2 sensor is brand new, will note that in first post.

[Syncronoid]

Where would one buy this "starter fluid" of which you speak??

[E1]

Any FLAPS, the canned stuff you start a car with in winter.

(mostly in the carburetor days)
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‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[Syncronoid]

So, one would expect the engine to surge momentarily when the starter fluid is ingested?

[Syncronoid]

Well, I'm always up for a challenge and taking risks, so I just performed said test with Valvoline Extra Strength Starting Fluid. Started engine and sprayed liberally in all the various places you would expect to have a vacuum leak in the engine bay. I observed no changes in idle.

Edit: Got a nice little buzz along the way.
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'90 Syncro Westy w/GW2.5L

[Syncronoid]

Bump.
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'90 Syncro Westy w/GW2.5L

[tjet]

I agree with a possible vac leak or restrictive exhaust. Easy enough to check on the exhaust. Loosen up a pipe connection and drive it all noisy.

The other scenario is that your timing moved when you replaced the dist cap. Is the cap on squarely? I also followed tencents advanced setting procedure on my RJE 2.2 WBX (+5 deg)

On your injectors, it's better to have your original ones rebuilt and avoiding new ones.

Are the plug wires the "correct" vw ones that have the threaded end plug retention feature? The upgraded plugs you should be running are NGK BP6ET

On the new dist cap, make sure the rotor contact button is ok. Do you have the old cap?

The last thing I would check is your AFM. Do you have a spare you can try?

Take a look at this video


Link

[Syncronoid]

Everything changed out didn't cause the problem, van drove fine for over 750 miles. Taking in for smoke test soon.