Just thought I'd share my experience;
Bought '98 156 2.0 TS last year, on the way home from the dealers the revs dipped so much approaching a roundabout it cut out. It was a cash in hand deal so had no real come back on the garage..
Anyway, the problem seemed to come and go and I've spent hours on this website trying to find the cure. I firstly cleaned the Throttle Body, this worked well ... but only for a week before the rev dipping returned. The cleaning of the Throttle body itself is not the hardest job in the world but I dont fancy having to do it every week!
Then I discovered that my Thermostat was not working properly [always ran cold, essentially the same as permanently leaving the choke out on an old car, needless to say MPG was poor and the car wasn't as responsive as I'd have expected]
New Thermostat changed the car, mpg went from 22/23 to 34/35 depending on journey type. Increase in power @ >2k revs which was nice
However still have rev dipping problem, I've bought a VAG-COM cable and just found time to do some work with AlfaDiag / Fiatecuscan. AlfaDiag wouldn't run on my machine for longer than 5mins. Fiatecuscan got going eventually but you cant reset the Idle Actuator on the Demo n I wasn't about to spend €50 on something which might
Came across this thread - http://www.alfaowner.com/Forum/alfa-147-156-and-gt/55388-156-wonky-idle-the-fix.html -
- It seems drastic but it's worked for me! Been out tonight on a test run, revs drop to maybe 600 ONCE then rock solid 850/900. no back and forth, no threat of stalling - Massively chuffed..
Sorry for the long post!