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Hi, new to the forum so hope you folks can help.

I'm the original owner of my stock '86 Vanagon...water cooled and fuel injected. Runs great, but has developed an idle problem. Upon start up, or after start up when at stoplights, you never know what RPM it is going to run at. Sometimes idles at normal 1K RPM, but other times idles around 2+K RPM. It's basically a crap shoot what the idle RPM will be any time you start up or take your foot off the gas when in neutral.

Any suggestions? If so, please also help by describing (or post a picture) where the part or adjustment to be investigated is found in the engine compartment.

Thanks in advance.

Hello!

Okay this is easy.

The problem is in the idle stabilizer (black box).
As as US car you should have a "MV" spec engine w DigiFant EFi.
The box is located in the RH of the engine bay.The easiest way to reach it is to remove the RH tailight assembly 4 philips screws.
Hey it's damm dirty in there!
Remove it from the connector and clean it up.If you see corroded contact pins try to clean them.Put some contact cleaner spray in both (pins-connector and put it again start the car and seed whta happen.Now there is two units available the 251 907 393 "B" and the later updated 251 907 "D".I think you have the "B" box.


Good luck

The idle stabilizer may not be the case. I have seen instances of bad oxygen sensor do this, bad ground off pin 19 of the ecu, as well as bad grounds in the engine bay. I would start by cleaning the grounds in the engine bay. Then, if you know the Oxygen sensor hasn't been replaced in forever, and the end of the tail pipe is sooty, there could be your problem. Last but not least i once had a van that the cat converter went bad on, and caused similar problems as you describe.

I agree but almost the 75% of the cases is the idle stabilizer box.
If is the os if you simply disconnect it the problem is solved!

Not quite as simple with the oxygen sensor. If you unplug it, yes your van will run. BUT, you are dropping part of the FI circuit that is measuring Oxygen in the exhaust and changing the mixture. With it unplugged, you go into a default mode which is pretty close to perfect on a brand new van, but really not on our old motors, or even rebuilt ones. There are probably instances in the power band where it runs rich or lean at this default setting.

I am not flaming you at all, just have tons of experience with these problematic cars and trying to share. I agree that if you have access to another relay from a friend's van or if you have a spare, by all means try it first...you are absolutely right on that. It takes 10 minutes top to test that.

Thanks for the replies and advice.

I followed up on the suggestion about cleaning the contacts on the idle stabilizer. The directions for how to find and identify it were perfect....I never would have found it otherwise. (FYI my van has the "B" unit). Anyway, the contacts and connectors did not look too bad but I cleaned them as best I could by scraping them with a fine tipped jewelers screwdriver and then swabbing them with isopropyl alcohol and q-tips. Only problem is that did not fix the idle...still randomly settles out at ~1K or ~2K RPM.

I ran out of time then, so sounds like the next thing to try is the oxygen sensor. Is there a way to actually check whether the sensor is bad, or do I just disconnect it and see if the idle stabilizes and if so conclude the O2 sensor is bad.

disconnect it and that will tell you. You usually will see soot at end of the tail pipe if it is bad, in my experiences.

Update....I tried disconnecting the O2 sensor while my Vanagon was idling about 2K RPM and there was no change...continued to idle @ 2KRPM. So the problem leading to the variable idle RPM remains to be found.

Any more suggestions of what to try next?

I don't want to send us off on a tangent, but could a thermostat have anything to do with this? I suspect my thermostat may be stuck open since most driving in this vehicle is short trips of 10 miles or less and the temp gauge almost never budges from being pegged on 'cold'.

Before blaming injection, have you thoroughly checked out ignition system? That could be part of it. Have you cleaned battery ground connections, as well as the ground straps from tranny to ground and motor block to chassis? This is not goofy...the FI is really sensitive and it can be these little things that send the system into this "hunting" mode......these also is a ground that comes from pin 19 of the ecu and grounds to the engine block. This ground can be the culprit...I have seen it a half a dozen times. You can run a new wire from the block and splice into the wire right before it goes into the ecu.

I know this is a little late into the discussion, but pull your TB and have a look for wear.

My 88s looked like hell, and occasionally stuck not quite fully closed.

Once I filled the huge gaps with JB weld, my idle air stabilizer started working.
(The switch setting were right before and after)

(Also "did" all the grounds etc, did not hurt, VW must think paint is conductive)

Full long winded post on the Wasser/T5 forum.

And yes, a stuck open Tstat is a likely culprit. I get to final temp in ~<5 miles, afetr a 1 min warm up in the driveway.(Highway 70MPH tho)
Mine "idles high" until it warms up.

It's off full cold before I leave my steet though... Off the stops anyway in < 2 min.

Just drove home, temp needle was at its normal ~50% position in <3 miles,(and stayed there) and I was "off the stop" on the temp gauge in <2 min, one was at idle, rest was getting of the TI campus@20mph.

I consider that normal operation of the thermostat.. YMMV.