Yet another "hesitation" problem, but not the usual one

[Stefano]

Hi, I have this hesitation problem on my '96 Aero non-TCS manual.
It doesn't happen at high boost (which would indicate a bad DI or plugs), rather it happens at small throttle inputs, when my boost gauge indicates between -0.2 and 0 bar. For example, it happens when I pull out of a junction: first gear is fine, second also is, until it reaches 2500rpm (pedal slightly pressed), where, insteda of simply stabilyzing speed and wait for third gear, the car starts to shudder (nothing major, but I still can feel it). If I give it more gas, it goes and subsequent acceleration is fine.
When I crawl around town at around 40km/h (30mph), I always feel that I can't keep a constant speed, either I decelerate or accelerate.
Also, it happened that during a re-acceleration after slowing down, the engine kinda missed a beat, just in the moment when the boost gauge was crossing the zero. After a split second, during when I didn't moved the pedal from the floor, the engine started pulling again a and boosted fine (0.9 bar) until redline. This happened only once, I wasn't able to re-create the situation again.

I already thought to replace air filter (30k km old) and fuel filter (no idea of its age, worst case it's 190k kms), I'm doing those as soon as I can. I'll change my DI with my spare one but I feel that it won't change anything. Plugs are gapped 1.0mm and 15k kms old. All vacuum hoses look fine. BPV valve is new (well the garage that fitted it told me it was, as they told me it's the a new copper-piston type).
Any other ideas? thanks in advance guys.

[Jim Mesthene]

Neither air filter, nor fuel filter could cause those symptoms. My guess would be the DI.
My wife's car ('92 N/A) would skip a beat once a minute and hesitate when cold until I replaced the cassette.

[Stefano]

Last night I swapped the DI with my spare one, the car *seems* to run smoother now (but still it may be an impression, didn't put much road on it yet).

The bad thing is that it now misfires badly on full boost That DI was perfect when I put it in my trunk less approx 9 months ago. Looks like it went bad just by sitting in the trunk . What did I do wrong?