20th Aug 2007, 00:54


I have a 1991 1.8L, manual transmission, Jetta GL. Over the past few weeks, it has developed a consistent problem with the idle following deceleration. The sequence is as follows: I depress the clutch as I am decelerating, the RPMs increase significantly and then immediately drop to around 500 or less, the quick drop in RPMs sometimes results in a complete stall. If it doesn't stall, then it returns to 750 RPMs as the ususal idle. I can't figure out what is causing the wild fluctuation in the RPMs during this one seqence of deceleration involving the clutch. Any ideas?

10th Sep 2007, 12:04

Hi! I got a '91 Cabriolet cheap because the seller was disgusted with it. He had sunk many $$$ into it without improvement. It was at the dealer so long the place dropped VW (or vice versa) and it wasn't even a VW place when I picked it up there!

Basically it starts good when cold and runs okay initially, but anywhere from 2-20 minutes later it will start idling very rough and stalling, bucking, etc. Sometimes you can put your foot to the floor and it just keeps stumbling and coughing. Other times that will get the RPMs up enough to keep it going, but its gutless for a few moments. Frequently it will get over it as fast as it got sick and it will pull hard. Only once or twice did I just get on the highway cold and keep on going and then it seemed okay; go figure! Point is, hot or cold are mostly okay. In between is where it has problems.

Ex-owner and former VW dealer changed air slow sensor, ignition module and ECU that I know of because I got the old parts. O2 sensor looks new. I changed CTS and (falling apart) knock sensor. I added a few additional grounds where I thought they might help. I put Stabilant on everything I could. It seemed improved for my efforts, but not for long. Two weeks, maybe.

Any ideas? This is the darndest thing! BTW: When it starts stumbling and stalling it smells like it's running very rich. That's funny because I think it's running like a car that's way lean! BTW: This is 2H engine, Digifant II.

Thanks! Don.

11th Sep 2007, 15:16

I have a '91 Jetta that won't start if it is wet. Heavy fog or rain and it will not turn over. Any suggestions? bmcenroe2002@yahoo.com

30th Nov 2007, 22:15

Hi, I read a couple of the comments and found similarities to some of the issues I am having with an '83 Scirocco (stalling, but only when it seems very hot outside). I found a VW recall site and found some very interesting in-line fuel pump recall notices, and will have to see if that is the issue I am experiencing. Later, I will try changing the relay and then look at the cable from the fuse panel as another possibility. Man, the time and parts so far, and it could be a simple recall issue - let's just hope so!

3rd Dec 2007, 10:35

I just purchased a '90 Volkswagen Jetta and recently, when I turn the car off, I hear a motor running in the back of the trunk on the drivers side. It goes off in about a minute, then starts back up again and doesn't stop until I turn the car on again (it'll go on all night). Any ideas?

25th Dec 2007, 22:09

Hey all, I have owned VWs my whole driving life and they do have some quirks, but are as reliable as they come if you look after them. The guy having trouble with the idle... check your Idle air stabilizer (Round thing with two wires to it on top of the valve cover) Turn your ignition on, but don't start the car... it should be buzzing. If not check the wiring to it or replace it with one from your local pick and pull. Also check for vacuum leaks, be sure your timing is set right as well or try turning the Idle air screw in the intake (by the butterfly valves). Hope you figure it out. I have almost 400,000 km on my '90 Jetta and it runs like a dream.

26th Dec 2007, 09:36

I have a 1992 Jetta GL that won't run when it rains. I plan on replacing the ignition coil as that seems to be the problem. (I replaced dist cap, button, plug wires, and found out the hard way that the coil shocks me if I touch the coil can.)

Recently though, the car starts fine, idles fine, until it gets warm, then it shuts off. I will look into the relay problem. I miss having a reliable VW.

19th Mar 2011, 20:55

This has been an awesome resource for answers.

Thank you to everyone who wrote here.

11th Jun 2014, 15:48

Same issue here.

11th Jun 2014, 20:10

Check the relay that controls the fuel pump. Had that problem with an old Audi - hairline crack on the solder.

11th Jun 2014, 23:23

If the coil is cracked, that could be the issue, as where they were located back then (near the firewall), rain water could easily run down and get into the coil, causing your issue.

I had a cracked one on my 1993 Cabriolet (which was one of the best cars I've ever owned), and replacing it solved the issue of rough running in the rain.

Still miss that car - never should have sold it. I should have parked it & covered it, occasionally charging the battery & running it. Would love to still own it.

Thankfully I still own a convertible, a 2001 Sebring LXi with the same color scheme inside & out as my beloved VW Cabriolet. It's also a wonderful car. This one I'm keeping as long as I possibly can.

1st Sep 2016, 03:05

Did you ever figure it out?