more idle surging and poor running in general

[borninabus]

86, 2.1:
i did some searching, but want to get some fresh input.

the symptom:
cannot lower idle below about 950 even w/ bypass screw closed.
idle surges w/ ISV plugged in. like a big, long surge up to about 2500 RPM for a couple seconds...then down...then back up...et al...

things i have done:
checked for vacuum leaks
verified correct operation of TPS.
tried multiple ISV valves. same result.
tried multiple idle control relays. same result.
replaced O2 sensor (used).
replaced TS2. (NAPA unit)
all new cap, rotor, plugs & wires.

things i think i should do:
Test CO values & O2 sensor to Bentley Specs.
test emission canister valve.
test power steering relay.

here's where you come in:

what else should i be looking at
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88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport

[Vanagon Nut]

plug TB inlet nipple and inlet at air intake boot "T" to eliminate EVAP valve et al. Easy.

So ISV valve unplugged, no idle surge? If so, have you cleaned it?

I know you swapped, but have you tested with ISV module disconnected? This would also take input parts (i.e. PS switch) out of the picture.

re: CO, if you're thinking AFM air bypass adjustment I"m pretty sure that even if CO screw backed out completely, the increased "bypass" air should be consistent and meterable via the idle screw at TB. From another POV, increasing amount of air bypassing AFM flap should mostly result in causing flap not to not open as much. So CO screw turned CCW, AFM tells ECU to lean mix, CW, rich. And my guess is that at idle, even if that air was getting past the TB valve (if worn), the idle shouldn't be going up/down like that.

Inspect AFM tracks for wear or just test voltage output. tencentlife did a great write up and video "how to" on this.


Neil.
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1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[Ahwahnee]

Sometime when it is surging -- undo the cap on the oil filler tube and see if the surging stops.

That's what mine would do before I resolved it.

[borninabus]

well, I had a little free time in-between working on other people's VWs to do something to mine:
I was getting some weird sounds from the (Cali) cats so I ditched the "must pass smog" custom cats & muff and replaced it with the stock set-up from my old van.
also adjusted the valves.
no love. the symptoms persist and they are:
surging up to about 2800 and falling down to 900 w/ ISV plugged in.
sometimes it sticks up high & won't fall back down.
I was also getting some surging under throttle (especially w/ light throttle) but only about 400rpm and poor idling; so I commenced to tinkering.

I unhooked the PS relay (on pump), no change.
next I unhooked the O2 sensor and it seemed to smooth out a bit.
I then opened the CO screw about 3/4 turn until it smoothed out even more.
it seemed to smell a little rich and honestly I have no idea how to set the CO so I'm just experimenting.

where I am at now is that it is running well, idling smoothly & no surging but I have the ISV & O2 sensor unhooked.
and it is not starting when cold unless I give it gas.

I guess @ this point I should bite the bullet and buy a new O2 sensor.

other suggestions welcome
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88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport

[wemfam]

I have a similar surging idle problem.......I took Ahwahnee's advice and removed the oil filler cap with it running, (and surging), and it smoothed out.....almost died due to low RPM, but it smoothed out. So what was your solution Ahwahanee?

[t_man]

I had similar surging issues. Being lazy, I skipped 10cent's diagnostic and bought a rebuilt AFM from Van Cafe. Problem solved. I tried cleaning the contact and bending the arm - the new-to-me unit did the trick.
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-tgc
'90 Westy Automatic

[borninabus]

i've been around with it quite a bit.

i did discover a worn AFM the someone had "tweaked".
so i replaced it with a better looking (on the inside ) unit.
replaced the throttle body w/ another used--and properly adjusted--unit.
swapped around ISVs & ICMs until i found a "working" combo.
took a run through the ProTraining and tested grounds ohms and what-nots.

seems to be running pretty sweet and getting 16+mpgs.
it still idlers poorly w/ the o2 sensor hooked up so i ponied up for a new one and it should be here soon.

one issue i am having is that the ISV is holding the idle up:
sometimes @ around 1100rpm and sometimes up as high as 16-1800rpm.
i can blip the throttle and get it to fall to around 1000.
i can measure 1.5+ volts @ the ISV when this is happening but...

if i unhook the ISV while the engine is running and then reconnect it; it stops.
idle drops, voltage @ ISV falls to <.5V...everything is normal.

subsequent restart of the engine w/ the ISV connected produces the same symptom.

so where is the voltage coming from and why?
...is the question i pose to anyone who is still listening
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88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport