8 valve Digifant Stalling and Rough Idle Thread to end all threads

[surfingpimp]

I have an 8 valve 1991 GTI and I have searched and searched and tried almost everything that has been posted. I though it would be good if people could post their personal experiences with these two topics and how they fixed them since they usualy cover related items. Also many people post having these problems but they usualy don't post to say that they fixed it and how they fixed it. Lets all work together to end these problems for everyone once and for all.

These are all the things that I have replaced sometimes it seems as if I have fixed it but the problems just come back I am running out of stuff to replace.
New Thermostat
New Vacum Lines.
New Coolant Sensor
Bosch Platnum+4 Plugs
Bosch Cap
Bosch Rotor
New Wires
Cleaned ISV
New Fuel Injector Seals

[quadmodrophenia]

Throw the platinum 4 plugs in the garbage, digi hates platinum 4. Go spend half the money and get the silvers and you'll thank yourself.
My ISV never acted up until I cleaned it, go figure. After removing AC and PS I just threw my ISV in the trash and plugged the holes. It's never idled or run better.

[ridefuel]

Quote, originally posted by quadmodrophenia »

Throw the platinum 4 plugs in the garbage, digi hates platinum 4. Go spend half the money and get the silvers and you'll thank yourself. My ISV never acted up until I cleaned it, go figure. After removing AC and PS I just threw my ISV in the trash and plugged the holes. It's never idled or run better.

Took me 5 min to remove mine and plug the holes.

[Black92EightValve]

bad O2 sensor or maybe Coolant Temp Sensor (CTS for short)....
I've had similar symptoms from both

[vwtoys]

on top of the wear parts, bad grounds can cause rough idling/stalling. That in combination with vacuum leaks will make things worse. Clean all grounds, connectors. Add an extra ground from the ECU to the Chassis.

[NeoMK2]

I recently had the same problems. Check these 3 things....

1 - Air Flow Sensor - The black box on top of the air box. (will be $$$...I paid $75 for rebuilt...about $200+ for new)

2 - Fuel Pressure Regulator - Gold looking fuel filter like unit just below and to the left of the fuel rail. (about $75)

3 - Air Idle Control Valve - The gold looking tube device just above the engine. (currently about $150)

I replaced 1 & 2 and now my car runs like a bat outta hell....MPG's shot up from 22 to 27

NeoMK2

[V-R-6]

Slowly move the throttle plate by hand and listen for a click when you first start moving it and right before it's fully closed. There is an idle switch directly below the wide open throttle switch on the throttle body. The lower switch tells the ecu that the engine is at idle or that the throttle is closed and the upper switch tells the ECU to richen the fuel mixture at WOT.

If that doesn't work try disconnecting the ISV and running the car without it. Also check your timing to make sure that is spot on.

[VW-BMW]

All 3 of my mk2s have had a problem with the AFM connector. After ziptying them so they aren't loose, the car always runs better.

It takes 3 or 4 zipties, make a circle around the black box on top, so the tab on the connector is inside the ziptie.

[Paxle]

check your spark gaps...

[L33t A2]

throw those damn bosch platium +4's in the trash and spend 1.58 on new single copper plugs at http://www.germanautoparts.com or for a hare less at http://www.autohausaz.com

[NeoMK2]

"My ISV never acted up until I cleaned it, go figure. After removing AC and PS I just threw my ISV in the trash and plugged the holes. It's never idled or run better."

ISV? What's that?


Modified by NeoMK2 at 3:30 PM 3-10-2005

[quadmodrophenia]

Idle stabilizer valve, it's the big metal cylinder on top of your valve cover, has a connector on the left hand side and some vacuum hoses going into it.

[surfingpimp]

I tooled around with my car for a bit today. I couldn't throw the bosch
+4s away so I put them in my spare parts box but I did throw in the cheapest plugs I could fine and I fidled with the MAF sensor connector and my car is running much better but not perfect. I would like to redo the entire engine wiring harness does anyone know where you can get a complete new one. After almost 15 years it seems as if most of the wiring is brittle. Also I am thinking of deleting the ISV Idle stabilizer valve but I know it has something to do with adjusting the idle when you turn on the air conditioning since I live in the south I use the A/C alot in the summer so I don't want to pull it out if it's gonna make me stall at every stop light this summer. Also I am interested in putting an extra ground to the ECU but I can't find any pictures or a more detailed explanation of how to do it. Keep up the posting I am sure this tread can help lots of people since stalling and bad idleing sre such common problems.

[V-R-6]

Did you check the crankcase breather grommet on the valve cover? When these go bad you can experience the symptoms you are having as well...

[surfingpimp]

PCV valve cover gromet has been made completely leak proof by some RTV black silicone. Still thinking it's the connection on the Air Flow Sensor.

In regards to vacum leaks I saw some interesting info but can't find the post again. Sometimes vacum line because of age will collapse upon themselves even though they don't leak. The collapsing of the hose cuts off the suction causing rough idle and stalling sypmtoms.

[mightywhitey]

Quote, originally posted by ridefuel »

Took me 5 min to remove mine and plug the holes.

What did you plug the holes with?

[jerminator]

my idle keeps fluctuating, and sometimes stalling at stop lights, but only after the car is up to temp, and it only acted up after i ran a bunch of injector, and engine cleaner through the gas.

one of my coolant sensors is garbage, so im replacing that, and would suggest it.

[T REDMK2GTI]

Quote, originally posted by vwtoys »

on top of the wear parts, bad grounds can cause rough idling/stalling. That in combination with vacuum leaks will make things worse. Clean all grounds, connectors. Add an extra ground from the ECU to the Chassis.

x2, this was the last thing i thought about when fixing my car, make all the difference

[Iced Golf]

Quote, originally posted by jerminator »

my idle keeps fluctuating, and sometimes stalling at stop lights, but only after the car is up to temp, and it only acted up after i ran a bunch of injector, and engine cleaner through the gas.

Change out your fuel filter, it's probably clogged from all engine cleaner loosining up the gas tank gunk.

[Neon Washer Nozzle]

If you get an o2 sensor just get a cheap one for an Escort and splice the connectors. It should be in the FAQ. The blue coolant sensor/new o2 sensor/cleaned ISV trifecta worked really well on my dad's beater. About 2 hours of work and $60 later and it idled dead on at 1K. And now that it doesn't have the a/c holding it back, it runs like a friggin' swiss clock.

[90Carat]

Wow, talk about back from the dead thread....

Anyway, here is what I did the other night to fix my bouncy idle.. After cleaing and ensuring that I had a working ISV, I drove around til the motor was nice and warm. Then:

Turn off the engine, unplugged the ISV and blue coolant sensor
Started motor, crazy low idle, adjusted idle screw, noticed it was loose.
Tuned off engine and reconnected ISV and blue coolant sensor.
No more bouncy idle.

Thought I was good to go.

Yesterday, car starts bouncing again. F@#(K!
In the parking lot of a grocery store, adjusted idle screw again
Then I went over to Home Depot, and got some loctite (not the red) to hold the screw in place.
After a little bit of loctite, looks like the problem is solved.

[Banditt007]

my digi seems to rev up and down up and down if the idle screw backs out too much, its like the car see's its reving too high and trys to compensate for it. once i screwd it in alittle bit to lower the idle problem went away immediatly. Weird thing is, is that it seems to back out, yet the o ring looks perfect.

[wgriffiths2000]

I have a problem where me engine will die when the rpm drop down from switching gear but not every time some times idle kicks in at the last min any one know if the aboved stuff would fix that?

P.S. This also occures on start up!!

[rychas1]

the idle screw o-ring fixed like 90% of my headaches. CTS and that darn AFM connector as well. (i just sprayed some electronic cleaner on the AFM connector, so far so good). grounds are next, even tho the car runs fine now.

[swmrdak79]

Lets bring this thread back.......

My car is having a similiar problem. When ever I push the clutch in my cars RPMs bounce from 750-2500. I have changed out:

Fuel filter
Blue sensor
readjusted idle screw
readjusted throtle cable tension
cleaned ISV
new plugs and wires
oil change

Please help!!!

[LJD_MK2]

I just have to say that I love this thread.

[Tuggle]

Quote, originally posted by swmrdak79 »

Lets bring this thread back....... My car is having a similiar problem. When ever I push the clutch in my cars RPMs bounce from 750-2500. I have changed out: Fuel filter Blue sensor readjusted idle screw readjusted throtle cable tension cleaned ISV new plugs and wires oil change Please help!!!

same here - all the same stuff plus new water temp sensor and new o2 and my car runs RICH!! someone suggested MAF

oh and parts
http://www.bestpricecarparts.com

[hatter36]

Other things to consider:

Throttle body switches - you have 2 switches on the throttle body - 1 for idle, and 1 for full throttle. All the wiring on those has broken on me at one point or another, so check that.

The idle screw has an o-ring around it. It can go brittle and let air through. Sounds like you have sealed it with the loctite though.

The throttle body innevatably gets gummed up; clean it out. The throttle plates could be sticking every so slightly open because of dirty. Also be sure to remove the idle screw and clean up the little air passages.

To check for vacuum leaks, and I have to admit it sounds like you have vacuum leaks, take a propane torch and run it (unlit) along your vacuum lines, intake boots, etc. You will notice a surge in idle if you have leaks.

[Tuggle]

Quote, originally posted by hatter36 »

Other things to consider: Throttle body switches - you have 2 switches on the throttle body - 1 for idle, and 1 for full throttle. All the wiring on those has broken on me at one point or another, so check that. The idle screw has an o-ring around it. It can go brittle and let air through. Sounds like you have sealed it with the loctite though. The throttle body innevatably gets gummed up; clean it out. The throttle plates could be sticking every so slightly open because of dirty. Also be sure to remove the idle screw and clean up the little air passages. To check for vacuum leaks, and I have to admit it sounds like you have vacuum leaks, take a propane torch and run it (unlit) along your vacuum lines, intake boots, etc. You will notice a surge in idle if you have leaks.

my tb is clean and i did re seal my screw.

[upand_at_them]

I add vote for cleaning the throttle body.

I had a horrible idle problem for several years. Up, down, up, down...stalled a lot too. Was hair pulling to drive it. I checked everything, several times. Then I removed the throttle body and thoroughly cleaned it, including the vacuum ports.

It idles normally now and has improved the overall driveability, because it's no longer doing funky things during gear changes.

Mike

[bee5099]

Quote, originally posted by wgriffiths2000 »

I have a problem where me engine will die when the rpm drop down from switching gear but not every time some times idle kicks in at the last min any one know if the aboved stuff would fix that? P.S. This also occures on start up!!

I'm looking at buying a mk2 8v jetta with these same symptoms. If anyone has but together a really good cure for this I'd like to know. It looks likes theres many ways to approach it, just curious if theres anyway to narrow it down. Also, when I accelerated I heard a small clicking noise, but not when I was in neutral revving the the engine. I also noticed a hard jerk when letting out the clutch in first, and reverse; bad motor mounts? Any ideas?

[Deutschbag]

Best solution is to swap in a full 2.0 crossflow engine + management, digi2 is garbage. But I'm only replying to this with that comment so I can subscribe to this thread, cuz I can't afford a new engine and I'm getting terrible mileage and having kind of bad idle.

[supapowies]

ok all off us are not super car savy with all the parts(such as myself ....sigh), does someone have or could make a reference picture diagram with some arrows to where the possible trouble parts could be im sure that would really help out alot. oh and a real life pic would be better not and illustration

[isha0018]

damn idle

[jem_whlz]

Quote, originally posted by supapowies »

ok all off us are not super car savy with all the parts(such as myself ....sigh), does someone have or could make a reference picture diagram with some arrows to where the possible trouble parts could be im sure that would really help out alot. oh and a real life pic would be better not and illustration

I'm the first to admit i'm just shy of Neanderthal when it comes to labeling parts on the actual car.

Then my uncle bought me a Bentley for Christmas. Don't have the car, but I kept the Bentley. (Figgered it'd come in handy again, since I've got this a2 virus...)

Save up your pennies, buy a Bentley. (not only will it help with the "what step do I do next?" questions, it can keep the car from rolling down the drive while you're doing the repairs.)