A2 Digifant hesitation puzzle

The car is a 1992 Canadian Jetta with Digifant. The main, reproducable symptom is a single momentary hesitation, somewhere between 2000-3000 RPM, whenever I transistion from coasting to aggressive acceleration. Just for a split second it feels like I've taken my foot off the gas and then stepped right back on it.

It's most noticable in the higher gears 3rd to 5th. Other related symptions are:

- occassional slight surging when coasting at low RPMs in 2nd or 3rd

- occassional random hesitation at highway speeds in 5th

- the idle seems to hunt a bit more than normal

- the timing at idle seems to bounce around more than I'd expect, although I've never really looked at it before since the spec calls for it to be set at 2500 RPM.

Newish parts (less than a year old) include plugs, rotor, distributor cap, O2 sensor, blue coolent temp sensor, air filter. I've done all the Digifant electrical tests in the Bentley...everything meters fine. Idle and WOT microswitches are fine. Timing is accurate. Power is fine otherwise. I've looked for vacumn leaks, tightened all grounds (including the usual ESU ground on the valve cover), cleaned out the idle stabilizer valve, and checked all electrical connections related to the ignition or ECU for corrosion... everything is bright and shiny. I've also run some high-strength injector cleaner.

This model of Digifant has no diagnostics and I really don't want to take this to the dealer 'cause they'll simply start replacing things... beginning with the $$$ ECU.

Anyone seen this ? Any thoughts of what I might have missed ? Right now I'm wondering if the airflow sensor is intermittant or has a flat spot on the wiper, but it could be fuel system as well.

Thanks in advance for any thoughts !

Vince

Reply to
Vince Waldon
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It still maybe that clean idle stabilizer valve. Try running with it disconnected for a test and see what happens!

I had to put one on the 88 Jetta that I have up for sale. Now the idle is rock solid. :-)

could be knock sensor.........did you check that? I guess you did since you check that when you check the timing advance. How is the CO setting? Air Flow box works properly and did you check with ohm meter? Did you change your oil?

later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris

Reply to
dave

How does one check a knock sensor? -another Dave with a digifant Jetta

Reply to
Dave McLaren

It is done when checking the timing per the Bentley instructions. You will be checking the distributor timing advance in a couple of different tests (engine warm and some things disconnected). If the advance does not vary enough they may be a problem. You will have to compare the max. advance between different test results to determine the condition of the knock sensor. Sometimes you might need to remove the knock sensor from the block, clean both surfaces and then carefully torque it back onto the block.

hope this makes some sense...but the Bentley should explain it! later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris

Reply to
dave

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