Hi All,

1985, 4+3 manual, Z51, 45k miles. All stock except 52mm BBK throttle body installed due to heavy air leak of original TB. My first and so far only Corvette, so I have no comparison with other Corvettes. The car runs great, no problems except this: there is noticeable change between situation without any throttle (when the car coasts with pedal released and gear in) and situation when I press the throttle pedal again. When I do so, there is something like light "twitch"... It is 100% related to fuel delivery into the engine. The same "twitch" happens when I drive with throttle pedal pressed and release it = noticeable "twitch" at the same moment when fuel consumption display shows 0 (l/100km). It was the same with original TB, so I would not suspect BBK. There are no other problems, clutch is brand new, manual transmission works perfectly with new oils and filter in overdrive unit. Overdrive has no influence to this - it is the same with or without it.

My question is - is this normal behaviour of 1985? Should the transition between "throttle ON" and "throttle OFF" or back be noticeable or should it be completely smooth?

Thanks,
Saip

 

It could be driveline lash, which would be normal.

 

I notice in my 85 4+3, that when RPM's are low, there is a noticeable "buck" that can develop when I allow engine speeds to get too slow. But no, there's no twitch whatsoever with my engine. Under normal circumstances, it's very smooth, on throttle to neutral throttle, to off throttle, and likewise in reverse. There's nothing noticeable at all like the "twitch" you have. I do have to check my universal joints, as occasionally, I'll hear a clank noise when starting up after a stop. But in trying to get my driveline to clank like that, at any speed at all, is impossible. It's very smooth. For all I know, it could even be brake pads within the caliper.
One thing I found with my car, was that all the rubber vacuum hoses were at the end of their lifespan, and I replaced them all with new silicone hoses. I found a couple, such as the hose from the cruise can to the brake pedal, to be paper thin, and would collapse under decent vacuum. This might be something to have a look for. Good luck!

 

I have a similar occurrence when the A/C or defrost is on. It acts like it is drawing power from the car. When the compressor kicks on, I lose a bit of power. When it kicks off, back to normal. This happens all the time and it is normal. Newer cars disconnect from the compressor at WOT so it doesn't draw power.

Could be a completely different occurrence from your issue but I think the "twitch" you are talking about motivated me to express my findings.