Idle Problem on '89 Golf

is it a carb or injection? for injection, i'd start by thoroughly cleaning the idle control valve, for a carb check for an induction leak- most likely the rubber spacer that the carb sits on

I believe you have Digifant II fuel injection.

has good maintenanceinfo on this system. Some (but not all) Digifant equipped cars have a set of two throttle position switches, one that closes at wide open throttle, the other closes when you take your foot off the accelerator. On my '87 (A2, not A1 and CIS-e, not Digifant) the WOT switch is in plain view on the top of the throttle body, the idle switch is hidden on the underside of the throttle body. My idle switch broke, and the idle speed went out of spec. Trying to find a replacement switch at the junk yard (CIS-e and Digifant uses the exact same switch, it is just wired a differently) I found that it was very common for this switch to be broken.

At

can see a photo of the throttle body with the WOT switch. Locatethis switch in your car. With the engine running (and presumably huntingup and down between 600 and 1000 RPM) press the lever of WOT switch.Does the idle settle down to where it should be? If so, you can becertain that the problem is with the idle switch. This test worksbecause on Digifant (but not CIS-e) the idle and the WOT switches arewired in parallel. The ECU figures out from the air flow signal whethera switch closure means WOT or idle the throttle body from below. The idle switch is right smack inthe middle of the photo. I am quite certain the '89 cabrio used the samethrottle body and switches as in the photo, but orientation of theassembly may be different from what I have described. If you find that you have to replace the idle switch, it will simplify things if you take out the throttle body first. Just remember to get a new gasket to put between the manifold and the TB. When I did mine, I took the opportunity to clean the TB as well. Aligning the new switch is not much of an issue, just make sure the throttle does not rest against the idle switch (the switch should be depressed at idle, but it should not stop the throttle from closing completely).

The idle switch is not available by itself, the dealer will sell you both switches with associated wiring and connector. This is not cheap. I found a replacement switch at the junk yard for next to nothing. Don't limit your search to Cabrios, look at all Jettas, Golfs and Cabrios. You will find that some cars have a 3-pin connector (CIS-e, '87 and older), some have a 2 pin connector (Digifant). For simplicity, try to find the latter, as it will fit without modification. I was not that lucky (I found only 2-pin ones, but needed the 3-pin variety). The switches are identical, so if need be, you can cut the broken switch out of your harness and solder in a working one from a different harness.

Hope this helps!

Randolph,

Thanks for all the great advice & suggestions! I'll break out the toolbox this weekend.

Cheers, Geoff Glave Vancouver, Canada

Correct me if I am wrong guys, but I read the Idle Air Stabilizer Valve can cause hunting idle too.

But I don't know how you'd test it - maybe one of the guru's in the group would know.

Chris

Geoff Glave wrote:

The Idle Air Stabilizer valve certainly *could* cause this kind of problem. This is very easy to mis-diagnose. You can remove and plug the air hoses to the IASV and see the RPM fluctuations go away, but this does not mean the IASV is bad. More likely some other failure is causing the idle control loop to go unstable, imposing an oscillation on the IASV.

Right. For instance, when I lost compression on a cylinder, I had the hunting idle issue. The ECU was trying to keep the O2 readings at spec, but couldn't figure out how to do that since it doesn't have separate readings for each injector (no car does). I'm thinking that a slipped timing belt might do the same thing as well.

I'd start with the basics. For instance, the '89 is horrible for corroded connections, most notably at the ECU itself. And, the grounds tend to corrode too. I'd make sure I had the right spark plugs in it, as that has historically been an issue with the '89. The cap and rotor are cheap too. The wires are expensive, but someone might wanna look at those too.

Ultimately, the Digifont system doesn't really tell you what is going on. The basic process for fixing any problem was "setting to specs" which included any number of sub-routines (sacrifice of a few virgins, etc).

Tim Wohlford '89 Golf, 245,000 miles (all of 'em mine) '98 Jetta

Forgot to mention in the original post... One of the cylinders does have bad compression. I just assumed this would lead to low power, so I discounted it.

However, you seem to be suggesting that it could cause hunting idle too... If it turns out this is the problem is there any solution other than a very expensive rebuild?

Cheers, Geoff Glave Vancouver, Canada