98 GLX Idle Problem

[rasafrasit]

I dropped off my car to have the ignition coil, plugs and plug wires replaced because the car was starting to stall on rainy days. While they were in there, the shop found that my timing chain tensioners were both disintegrating (powerfully expensive trip to the shop that week). When I got the car back it was doing a very strange thing at idle: if I sat for more than 10-15 seconds (i.e at a light rather than a stop sign) the engine would start to build a slight shudder as if it were missing on one cylinder and the idle would "fishbite" then it would behave almost as if somebody had unplugged it and immediately plugged it back in. That is, the interior lights would dim slightly and the engine would almost stall and then come back to life.

The shop found that the plug wires were bad and that one was arcing so I was getting weird kv readings so they replaced with OEM parts (not sure why they didn't in the first place). However the car still misbehaved so they did a compression test and found that cylinder 6 had 25% loss so they did a engine soak/vac and replced the valve gaskets. The car still did it, so they replaced the MAF. But the car STILL freaking does it although not as badly.

Yesterday, I had them run a oil pressure guage into the cockpit but it seems the oil pressure is unrelated (i.e it runs at around 15 psi when its warm and idling and rarely breaks 70 under load/acceleration). The severity of the "kick" is engine and external temerature related-i.e., the colder they both are, the worse the problem is. Furthermore, it doesn't always do it. Some days I can drive the car all day without it happening once. I can usually tell it going to be doing it by the way the engine sounds when I start the car-sort of rough and with some odd noises like a fan or a belt going bad. On top of that, the car runs fine on the highway/under load so its not likely to be the fuel pump.

On a final note, the car has never once thrown an error code throughout any of this.

What the heck is the problem? Has anybody else ever seen or heard of this?

[boschmann]

VR6 coils are notorious to fail, I'm unsure how the warranty is laid out as VW is replacing them in the newer models first & extended warranty may not apply to your vehicle. I've seen a thread somewhere on how to do a pin test on the transistors to check it out. Try a search on "VR6 coil transistor" if you question if it's bad or not.

[rasafrasit]

Originally Posted by boschmann

VR6 coils are notorious to fail, I'm unsure how the warranty is laid out as VW is replacing them in the newer models first & extended warranty may not apply to your vehicle. I've seen a thread somewhere on how to do a pin test on the transistors to check it out. Try a search on "VR6 coil transistor" if you question if it's bad or not.

Boschmann-

Thanks for the reply. I'm well past warranty (130K). I'll have the shop check the coil transistor pins (I've maintained from the beginning that either replacement coil pack is bad or the alternator is going-I am leaning to the former given that the car did not do this prior to the installation of the new c.p.). I searched here, VWVortex and Google for VR6 coil transistor (and similar searches) to no avail.

Thanks again,

Ezra

[boschmann]

Sorry, I located that thread & it was on a '98 w/AEB 4cyl engine which uses a different coil module & coil packs which will not test the same as your AAA engine. Are you checking for codes with a VAG scanner or simulator, as it will pick up things a generic will not?

[rasafrasit]

Boschmann-

Thanks for looking, I did find a few seemingly relevant discussions elsewhere that I have passed on to the mechanics. Not sure what their dignostic tools are but I am pretty sure they are using VAG-based tool. I'll check with them and see. In the meantime, any thoughts on the nature of hte problem are still welcome.


Thanks again