High idle: help with the hunt

[KBake]

I have a high idle problem with my 1986 2.1L, when I cold start I get pretty solid idle at 1000-1100 rpm. Once I get moving the idle bounces around 1500-1700 and then eventually when warm it almost always pegs at 2000rpm. If I sit at a light or park and leave on it will eventually drop back to that 1500-1700 range.

He is a list of recent R&R

1) Replaced entire exhaust system including a new o2 sensor.- made idle a little better but once warm returns to 2000 rpm

2) Replaced the air intake with brand new GW intake. When I pulled the old one off the TPS was not working at idle position and there was definite play in the body. I was sure that was the culprit. - At first it seemed to work and now it has gone right back to the above conditions.

3)Cleaned grounds and R&R engine strap. - no change.

I have a temp II sensor but don't believe the current is faulty. I also have pulled the module from the passenger tail light and opened it up to inspect for burnt circuits but it honestly looks good.

The next R&R that I am leaning towards is the mass air flow unit. I have heard a lot of idle issues get resolved when this is replaced but I thought I would reach out to the collective before I drop more coin on my van. I just got some new vacuum lines in and plan to replace but I don't believe there are any major leaks.

[hdenter]

STOP! Put down the credit card and take three steps back. Throwing parts at it won't fix it. Download the digifant pro manual from here somewhere and test the components. Your first clue is that the car idles fine when it's cold. That means most of the components like your AFM and throttle body are fine and the car works when in open loop. It's when the engine has warmed up and goes closed loop that things get crazy. Test your T2, test the harnes. Test the wire to the O2...

Hans
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'79 triple white convertible bug
'84 sunroof vanagon
'85 weekender

[Howesight]

There is a useful publication on the Digifant EFI system called the "Digifant Pro-Training Manual". It is more useful than the Bentley manual because it explains how the various systems and parts actually work, rather than just spitting out test procedures intended for trained auto technicians.

The Idle Stabilizer Valve (ISV) is the actual device that does the work of controlling idle speed. It can get contaminated in the portion of the device that does the task. Sometimes, the function can be effectively restored by cleaning with an appropriate solvent (like carburetor cleaner or lacquer thinner), blowing it out with compressed air, and then squirting WD-40 into it for lubrication. They are pretty robust units, so this often restores function.

A key electric signal input into the Idle Control Unit is the signal from the Throttle Switch, which must be correctly adjusted to do its job. Before throwing any more parts at your rig, I would suggest checking those items out.

The Idle Speed Controller ("ISC") is the small electronic printed circuit board inside a flimsy box in a poorly-chosen location (behind the tail light) which can suffer damage from water and/or road salt intrusion. They are repairable and several vendors sell refurbished units. It this part is defective, a quick visual inspection of the PCB will usually tell you whether salt or water exposure has damaged the unit.
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'86 Syncro Westy SVX

[KBake]

Relax I tested the parts before I replaced and they were due even if they weren't a part of the problem. I literally just stumbled upon the training manual right after I posted this. I don't have any reason to believe that the t2 is faulty cause it seems to operate the temp gauge fine. I guess I could test the harness and the O2 sensor. However I believe they are working.

I have not messed with the ISV because the PO removed the A/C and when he did for whatever reason in his mind he cut the cable to the ISV. But as far as I understand that only controls the idle under load of the A/C which I don't have. So I would assume as long as it stays closed it has no effect. I have owned the van for 3 years, and for the first two it idled with no problem with the cut ISV.

I also looked at ISC and looks to be in good order. If that closed loop theory is correct it seem that it wouldn't be the issues at hand.

[zerotofifty]

try adjusting the throttle body bypass screw when she is warmed up. She may be adjusted too high. The idle valve then should compensate when cold by opening more, as a cold motor needs a faster idle, more air. And/or confirm the throttle position switch is indeed closed when it should be. It can be a touchy adjustment.
Since you installed a new throttle body (not called an intake) that is were I will first look, it may well need the bypass adjusted and / or switch adjusted. Of course make sure the throttle body to manifold gasket is correctly inplace.
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