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