Fluctuating idle

[BlizzofOZ]

I have a '92 Jetta GL and last few days I've been noticing something funky going on with starting and idle.

Getting cooler up here in CT and last few days, trying to start takes a bit. Turning over strong. Pump gas a bit (not sure if that helps), but after two or three tries, it starts. Threw on batter charger overnight just in case, didn't help. Battery is like 1-2 years old.

After cold start, idle is fluctuating low to high, low to high, etc. Don't notice any loss of power when driving, but it hasn't warmed up yet and coming to a stop, idle is flucuating. Sometimes it almost seems like it will stall. Occasionally, tapping the gas and releasing quickly, the idle drops dramtically and then jumps high.

Once the car is warm, seems ok. After killing ignition, will start with no issues.

Any ideas of what to look at/for?

[Sab3r]

I just bought a Mk2 16v and mine had the same problem.

I took out the ISV and used WD-40 (I know what carb cleaner does to things, I work at a shop that uses it every day and its eats stuff alive) then took a air compressor too it. Then I added fuel injector cleaner and 93 non ethanol fuel too it. It runs so smooth now. Most of my ideling problems have gone away but there are some little hicups every now and again.

Ive been told to reground the cold start injector with 24g wire i believe it was to the engine? Who knows. You can go back to my introduction topic and read down where he tells me what too do. Also check your injector seals.

Other then that, im new to the whole VW thing so good luck man, sorry if none of this helped.

[Fischmonster]

Check your vacuum lines, does it idle rough after its warm?

[Seax_Smith]

8 valve digi II?

Clean and confirm the grounds with a multimeter.

Use starter fluid to locate vac leaks and repair them.

WITH THE CAR OFF AND KEYS ON THE DASH, disconnect each plug socket connection; clean with contact cleaner and reinstall with dielectric grease.

Remove ISV and clean with WD40 and be sure to get 12 volts across the terminals so you can clean behind the valve as well.

Reset the timing and idle per Bentley manual.

This solves 85%-90% of digi issues.

Hows the valver cover grommet for the UFO?
Have you ever checked your throttle switches?
Be sure your dip stick is seated correctly and sealing. As far a digi II is concerned that can be a legit vacuum leak despite what most people think.

[J.Knipl]

8 valve digi II?

Clean and confirm the grounds with a multimeter.

Use starter fluid to locate vac leaks and repair them.

WITH THE CAR OFF AND KEYS ON THE DASH, disconnect each plug socket connection; clean with contact cleaner and reinstall with dielectric grease.

Remove ISV and clean with WD40 and be sure to get 12 volts across the terminals so you can clean behind the valve as well.

Reset the timing and idle per Bentley manual.

This solves 85%-90% of digi issues.

Hows the valver cover grommet for the UFO?
Have you ever checked your throttle switches?
Be sure your dip stick is seated correctly and sealing. As far a digi II is concerned that can be a legit vacuum leak despite what most people think.

What happened to your website , that used to be my go to site at the first hint of trouble?

[Seax_Smith]

What happened to your website , that used to be my go to site at the first hint of trouble?

Changed service providers (lost the free web space) and never put it back up (on the new free web space). Also lost my URL cause I wasn't using it and forgot to pay for it.

Only a couple of people actually asked, so I wasn't too motivated to put the time and effort into it. Could probably resurrect enough of it to get it onto a CD if you want a copy.

If you are collecting Digi stuff: http://forums.vwvortex.com/showthrea...-challanged%29

[dunc12]

I had the same problem with my old digi II: bouncing idle when cold, stumbling when tapping the gas. Turned out my throttle switches were bad. I'd check those with a multimeter, and listen for the faint click when they engage/disengage. Good luck

[BlizzofOZ]

I've removed and cleaned out the ISV. Seems to be running better, I'm not getting the up and down of the idle (much). Now I seem to get slight... skipping. Almost as if a spark plug is not firing, but it is not consistant or evenly timed.

Still having issues starting when cold, but it still started.
This morning seemed a bit colder and now it wont even start. Again, it turns over, but won't start.

I had no more than a year ago replaced vacuum lines and such. Clean some of the grounds... not sure where they all are.

Still think the ISV? Just may be at the point of needed replacement?
I believe this is a Digi II... there is no cold start valve on this, correct?

[Seax_Smith]

I've removed and cleaned out the ISV. Seems to be running better, I'm not getting the up and down of the idle (much). Now I seem to get slight... skipping. Almost as if a spark plug is not firing, but it is not consistant or evenly timed.

Still having issues starting when cold, but it still started.
This morning seemed a bit colder and now it wont even start. Again, it turns over, but won't start.

I had no more than a year ago replaced vacuum lines and such. Clean some of the grounds... not sure where they all are.

Still think the ISV? Just may be at the point of needed replacement?
I believe this is a Digi II... there is no cold start valve on this, correct?

This will help with the digi II grounds: http://forums.vwvortex.com/showthrea...-challanged%29

[BlizzofOZ]

Got a used ISV and threw it in... still doing the same thing.

Ok, so throttle switches... how exactly do I test?
Would that be the next possible culprit?

[Seax_Smith]

Bentley is pretty clear, and I don't feel like typing. Warning: you need a multimeter.

Did you bother to clean it out first?

Have you actually done a resistance check on the grounds and actually checked for vac leaks?

Testing and replacing stuff does no good until the grounds and vac leaks are addressed.

[BlizzofOZ]

Bentley is pretty clear, and I don't feel like typing. Warning: you need a multimeter.

Did you bother to clean it out first?

Have you actually done a resistance check on the grounds and actually checked for vac leaks?

Testing and replacing stuff does no good until the grounds and vac leaks are addressed.

Yes, I cleaned out my old ISV first as suggested, but still same problem. Cleaned and replaced with used one, same problem.

Before replacing the ISV, starting is gradually getting worse, to the point where it just about starts. After starting, get flucuating idle.

Replaced the throttle switches, same problem in hard starting.

I had replaced the vac lines about 6 months ago. These are the ones located to the left of the ISV. Not sure if there are others.

Now, for grounds... I'm still unclear where/how I'm checking. This is in the Bentley?
Or are you referring checking the throttle switches is in the Bentlely?
I do have access to a multimeter...

[Seax_Smith]

Was referring to the throttle switches being in the Bentley.

Vac Leaks: Lots of options here. Charcoal cansister and lines, air box a lines, Oil dip stick seal, idle screw o-ring, injector seals, throttle body gasket, valve cover gasket, mis routing the vac lines with a 'bay clean up', HVAc system, reservior and check valve, brake booster, boot fron air box to throttle body, intake manifold gasket,and sure I missed a few.

Get a can of starter fluid and do light sprays on anything and everything the can be traced back from the intake manifold. when you find an RPM increase, you found a vac leak.

Grounds: BE SURE THE CAR IS OFF AND THE KEYS ARE OUT OF THE IGNITION! Primary batter ground from the battery, through the trans to the block, several on the stud in back of the battery tray, a group of three or four in the side of the head near the side coolant flange.

You can learn how to check for resistance on the web with a google search. Get out the emery paper and the dielectric grease.

Disconnect the digi harness from the ECU and check:

ECU Pin 6:
(65 / 174) Sensor Grounds: Brown / White →
A. Hall Sender Brown / White pin 1/-, &
B. Coolant Temp Sensor [CTS] Brown / White pin 2, &
C. Air Flow Sensor Potentiometer Brown / White pin 4, &
D. T2u/1 Brown / White pin 1.
T2u/1-2 is Throttle Switches plug / socket

[NOTE: There are four wires factory-fused together which comprise this bundle. The bundle and fused splices are contained inside the Digifant II harness. All four sensor grounds go to pin 6 of the Digifant ECU.]

ECU Pin 13:
(73 / 174, 10 / 172) Ground, Battery: Brown → direct battery ground.

There is more to read here: http://forums.vwvortex.com/showthrea...-challanged%29

If you have doubled check and are positive you have no vac leaks and no ground issues, then you are stuck testing components and confirming wires. As for which wires to check, see the link above. As for how to check the components, consult your Bentley. DO NOT disconnect the ISV with the car running, car "on" nor turn the car on with it disconnected. To test it you need to back probe the plug.

[BlizzofOZ]

First, I wanted to thank you for posting... and for posting all this info!

Once I finally got the car started:

Sprayed starter fluid in and around air box to throttle body... nothing. No jump in revs.

Now that car is started and running, flucuating idle is gone. So I think the throttle switches my have been that problem.
Which leads me to believe I just may have two different problems going on at the same time.
Now I'm just having issue with getting the car started.

[Nimyad]

I'm having the same prob except mine starts fine, it just will not stay at a constant idle. Just sitting the idle will bounce between 900-1000 non stop and coming up to a stop when I take it out of gear the idle drop severely (has died a few times on my). I cleaned the 2 sensors on the radiator hose and checked for vacuum leaks (which there are none). Any other thoughts? I'm planning on getting some injector cleaner tomorrow

[Seax_Smith]

Glad it worked out for you... wait your digi will rebel again... compounded digi issue - whudathunkit

[Seax_Smith]

I'm having the same prob except mine starts fine, it just will not stay at a constant idle. Just sitting the idle will bounce between 900-1000 non stop and coming up to a stop when I take it out of gear the idle drop severely (has died a few times on my). I cleaned the 2 sensors on the radiator hose and checked for vacuum leaks (which there are none). Any other thoughts? I'm planning on getting some injector cleaner tomorrow

What you are asking for is already in this thread.