Well, it took me 2 months and lots of searching to find out why my engine would vibrate from 3000 rpm up.

I thought it was the clutch disc so I pulled it out and put a new one in,,,, vibe still there, then replaced my timing chain because it was loose,,,,, vibe still there, then had my injectors tested by Rich at Cruzin Performance, ,,,, vibe still there, then pulled my valve covers and checked the lifters and rockers and rset my valve lash, ,,,, vibe still there, then pulled the distributorand found it to be ok,,,, vibe still there, ,,,, then unhooked the MSD 6AL and the vibration was still there .

Turned out to be an intermittent problem with a faulty TPS sensor, the TPS sensor would never go above 1.0 volts during accelertion, but never thropugh a code,, and that messed up the info feed to the ECM, so when I reved the car, the ECM tried to adjust ony as much as the idle air block info would allow.

Interesting ... glad you found the issue!

That's a strange one. Hard to believe it wouldn't log a code. My TPS has been known to log codes just because it was in a bad mood, I think!
Glad you finally pinned down the problem.

hi

i recently helped a friend with a 89 Vette, ´730ECM...

his ECM was bad, and didnt take any voltage from the TPS...according to Datamaster, TPS was always at 1.000 Volts, and..DIDN´T set a code...

That is interesting....I'm having an off idle vibration problem on my 92ZR1 & it was suggested to me by a member that the TPS could be the problem. Its my understanding that theres a carbon track inside the TPS itself & sometimes the track wears thin where it shouldnt be. Its like a rheostat (dimmer switch) & votage decreases with throttle position.

The area on the TPS where the throttle spends alot of time can wear thin & cause a false voltage reading to the ECM in turn causing a miss at that position.

I am working on getting a scanner to see what the readings look like.

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I hear you ...

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Just connect a voltmeter to the TPS, then turn your ignition on, but do not start the car, then read the volts as you move the throttle blades by hand.

Voltage should start at .XX and go up as you open the throttle body blades.

Holy Smokes!! You musta pulled your hair out finding that one, I never would have guessed.

Something to make a note of and keep in mind for sure.
Good job on tracing that one down!