85 Vanagon idles fine for two minutes then starts surging

tkdkrav

Howdy,

Sorry if this is a duplicate thread but I couldn't find anything on the forums that quite matched up with an issue I'm having:

85 Vanagon GL 1.9 L Digijet

All sensors pass mechanical and resistance tests.

I was having a very rough cold idle problem so I changed out all the vacuum lines. Problem seemed to be fixed until about 2 mins at idle passed.

Now it seems to idle perfectly until it reaches a certain temperature and then starts surging. I turn engine off then back on and it surges, but if I let it cool down for about 15 mins it idles fine then when it hits that warmer temperature again it surges.

While it's surging I unplugged the temp II sensor and the idle shot up, but it was steady. I believe by doing this I signaled to the ECM to enrich fuel mixture because I took away the ECM's ability to register a higher voltage from the temp II sensor.

Is it possible that there is still a minor leak somewhere and as the fuel mixture leans out due to increased temperature that the fuel/air ratio is too lean again? Or does this sound like a possible sensor malfunction?

Any input is appreciated!

Captain Pike · Posted: Tue Nov 20, 2012 11:58 am Post subject:

Did you bypass the idle stab box yet?
_________________
LEARN TO SELF RESCUE
59 Panel bus, 1966 Single cab. 73' 181. 73 Westy. 91' H6 Vanagon 3.3L.
.....................All Current.......................

tkdkrav · Posted: Tue Nov 20, 2012 1:04 pm Post subject:

I took a look and it turns out it was already bypassed. I plugged in to stabilizer box and produced same results. It ran like a top until it reached that magical temperature and then it started the revving again. I pulled my oil filler cap Off and it almost screeched to a halt so I put it back on.

This time, tho, I smelled a rich fuel mixture. I'm starting to suspect that temp II sensor now more than a vacuum leak. It's like it's trying to switch to closed loop but just can't seem to switch over for some reason...

adamjjohn203 · Posted: Tue Nov 20, 2012 2:33 pm Post subject:

Try the temp II sensor....if that doesn't help try to test a different idle control relay. Mine was working but not correctly. Cleared up my warm idle surging.
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tkdkrav · Posted: Tue Nov 20, 2012 4:04 pm Post subject:

Thanks for the input - just purchased the sensor from my parts guy. When I get back home I'll plug it in and let ya know!

mattcfish · Posted: Tue Nov 20, 2012 4:51 pm Post subject:

Just for chuckles, have you done the auxilary air valve test? When cold, clamping off the hose from the aux.air to the TB will change idle. When hot (after about a minute) it should not. If it does your air valve is leaking and needs to be replaced.
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76 BMW R90S
85 Vanagon with 2.2L upgrade

tkdkrav · Posted: Tue Nov 20, 2012 5:05 pm Post subject:

Yup I did the auxiliary air valve test a few days back - found several vacuum leaks in that area when I was testing. All has been set right on those hoses now.

I also took the valve off and put it in the freezer and it was wide open then put a hair drier on it and it shut almost completely when it was warmed up.

If the temp II sensor doesn't work, I may head back in that direction for one more look over. Thanks for the suggestion!

tkdkrav · Posted: Wed Nov 21, 2012 8:32 am Post subject:

Okie dokie - swapped out temp sensors and no change. It idled for three minutes this time before the surging started again (my guess is because it's colder today).

2 things I noticed: I'm pretty darn low on coolant due to some other work I was doing and never replaced what fell out of the hoses. I'll pick some up today and see if that helps. Maybe the sensor isn't submerged?

2nd the ground wire on the power steering pump was completely detached - I obviously need to fix that issue, but would that cause surging as the engine warms up?

Many thanks!

Terry Kay · Banned Joined: June 22, 2003 Posts: 13331

Three things to check if the idle runs up, and then runs down--

Vacuum Leaks, Evaportative Emissions control valve leaking, saturated charcoal cannister.

These items will create the problem your describing.
_________________
T.K.

tkdkrav · Posted: Wed Nov 21, 2012 10:50 am Post subject:

Thanks for the input! How do I check if the charcoal canister is saturated?

Terry Kay · Banned Joined: June 22, 2003 Posts: 13331

Is it the original cannister?
I'd have to say right off the top of my head that after 27 some years of use it isn't in tip top shape.

Really doesn't make much difference now anyway--
They are NLA--all gone--kaput.

I know the Van Cafe had 30 of them and they are all gone, & I had 45 of them and they are gone also.

Your going to have to tear it apart, reload it with charcoal-- & glue it up.
_________________
T.K.

tkdkrav · Posted: Wed Nov 21, 2012 12:15 pm Post subject:

I'm not sure if it's the original as I'm the 4th owner. I'd be willing to bet it is tho. I'm up for a challenge (or i wouldn't have bought the Vanagon haha) so I'll take look down this road.

Thanks for all the input everybody - you've given me great launching points for investigation. I'll let ya know my findings!

randywebb · Posted: Wed Nov 21, 2012 1:20 pm Post subject:

charcoal canisters are good until they [1] break in half, or [2] get liquid fuel in them
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tkdkrav · Posted: Wed Nov 21, 2012 3:14 pm Post subject:

Ah good to know. I doubt raw fuel is going in there. I feel it would run crappy cold too if that were the case.

wemfam · Posted: Wed Nov 21, 2012 5:57 pm Post subject:

following with interest...I too have the same problem.

mrlimbo · Posted: Wed Nov 21, 2012 6:38 pm Post subject:

When you say surges, do you mean the engine revs up and then hits say 1500-1800 RPMs and then the idle drops?

What is happening is when the engine idle is climbing and the throttle is closed, engaging the throttle switch, the ECM shuts the fuel off. Then the RPM drops and the fuel comes back on. The RPMS start to rise again and the process starts again. The throttle switch serves two purposes. First at full throttle the switch by-passes the oxygen sensor circuit and richens up the mixture slightly. Then on deceleration, when the switch is engaged the fuel is shut off. It helps save gas and slow the van down quicker.

If the idle is surging up and down, try this.. unplug a wire going to the throttle body. Does the RPM go up and stabilize? Probably idling about 1800-2000 RPMs. Try turning the idle screw in and see if the idle starts to drop. If not, sounds like a vacuum leak. You've mentioned replacing vacuum hoses, did you check the intake boots at the center section? How about the intake boot between the throttle body and air flow meter? I'd try tightening the bolts that hold the intakes to the head. I'd spray a little carb clean or something like that around hose connections and see if anything changes. If the idle does drop when you turn the screw in, turn it in until you reach about 800-900 RPMS and plug the wire back in and forget about it. I've seen this before.. Never quiet figured out why the idle changes, but it only seems to happen to the 1.9L.
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'87 Vanagon GL (daily driver)
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Terry Kay · Banned Joined: June 22, 2003 Posts: 13331

All of the above is correct--
IF he has a late model 1.9 with one TPS.

And being the Van is on it's forth victim, it's very well possible that somebody back down the road has foolishly tried to correct the up & down idling problem by screwing the primary adjustment screw in--which totally has eliminated the proper gap setting & messed up the TPS operation, and will cause the idle to fluctuate.

But---If he has an early 1.9 he has two switches, one for low speed & the other for high speed operation.
If they are out of adjustment & not functioning at the right time--the same would be happening.

So--first he has do determine what TPS he has--early or late, and how it's set, or working at all.

Then check for the vacuum leaks.

The cannister is pretty much on a vacuum all of the time--depending if the swich is working.
If it's leaking , the cannister is leaking , or saturated--it'll cause a searching idle.

To verify--check out the Digijet or Digifant section of the Pro-Training Manual.
It'll explain the same symptoms in the same places, and the correct cures.
_________________
T.K.

tkdkrav · Posted: Wed Nov 21, 2012 8:45 pm Post subject:

I have only one TPS. If clicks at shut idle and fully open. I also get 0 ohms at closed and 0 ohms at fully open.

I won't be able to experiment til after thanksgiving, but I'll let everybody know how it all goes when I get back. Thanks!

Terry Kay · Banned Joined: June 22, 2003 Posts: 13331

How much vacuum do you show at idle--on the line off of the back side of the throttle body?

It should be zero also.
_________________
T.K.

tkdkrav · Posted: Thu Nov 22, 2012 11:44 am Post subject:

And the prize goes to mrlimbo!

I waited for engine to warm and surging started again. I unplugged TPS and the idle went up but steadied. I brought the idle down via teh screw on the throttle bodie. It took a little trial and error to get where i wanted it, but eventually everything leveled out! Super grateful for everybody's help!

Now here's the question of the day - have I remedied a symptom or the actual problem? This bad boy has gotta pass smog. Is there an inexpensive way to test my emissions without going to the smog place or do I just do the best I can and cross my fingers?


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85 Vanagon idles fine for two minutes then starts surging
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