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Discussion Starter · #1 ·
I just bought this 1997 Z28 a couple of weeks ago. It ran kinda sluggish and had a slight vibration when I picked it up.
Getting home, I found out it did have some problems: SES on, 6 DTC's (P0400, P0300, P1441, P0171, P0161, P0131), bad trans mount (rubber).
I changed the TPS, IAC, all four O2 sensors, trans mount (poly). It now runs much better with good throttle response and good power. P0400 is still there (car has EGR blocked off) and SES is on.

BUT now the engine vibration has become much more noticeable. It's starting right off idle and increases with revs. From around 2500 you can clearly feel it in the seats.
It seems to come from the rear of the engine or transmission - if you pop the hood and rev it from there all is smooth in the engine bay.
When you put it in drive and go the vibration is still there but less severe (it feels like it is dampened by the transmission).

It feels like a balance issue (repetitive oscillation, not random/breaking up like a misfire). I have tested all cylinders by disconnecting one injector at the time - all cylinders responded in the same way by dropping revs (at idle). Previous owner changed spark plugs.

Here is a video of the vibration. Not very clear but I don't want to push it harder than necessary right now.

Next step is to check flexplate and torque converter. LT1's are externally balanced in the rear right?

Any ideas?
 

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Discussion Starter · #2 · (Edited)
UPDATE

I checked the harmonic balancer and torque converter and all looks good. Found two broken teeth on the flexplate though (that explains the banging during cranking). Lucky me...
Vibration was still present with TC disconnected but the idle started to wander a little. See video:

Then I decided to check the injectors again. Pulled one connector after the other and watched for any change (at idle and 1500 rpm). When I got to number 4 nothing happened at first, it seemed dead. Then all of a sudden the engine started clanking, showed DTC P0200 (Injector circuit open), and the connector was wet with gas. See video and picture:
32686


So I think the culprit might have been a bad injector all along.
 

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Discussion Starter · #3 ·
Ok, thought I'd update this monologue :) The source of the vibration was indeed a bad injector but also the poly trans mount (Energy Suspension). I put in a set of Accel #24 injectors and engine purs like a kitten now. Also changed the poly mount for a stock rubber one and now car is totally smooth.
 
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