I have a 87 Jetta coupe with CIS (not CIS-E) injection and MT. For a while, when I accelerate from idle at partial throttle, it will shudder and buckle between 1 and 2K RPM, sometimes even getting close to 3K RPM. Only way around it is to keep the rpm high and eat the clutch. Interestingly enough, AFAIK it does not happen when I am in reverse... but that could be since I do not tend to drive around in reverse.
What should I look into? The car idles quite nicely (+-50 rpm) and does start right up no matter the weather or time of the day or when was the last time I drove it. The fuel filter is about 3 months old. The air filter I replaced in October of last year; I guess I should check it too just to be on the safe side. I also replaced the o-rings for the fuel injectors this weekend, but am yet to check the spray pattern. After reading some posts here and even the manual, I did replace all the vaccum rubber hoses (AFAIK) in the engine compartment. No change. Anything else I should check?