Hello again Camaro Forums. My 95, 3.4 started this random dead miss at idle, and sputtering with a slight backfire and popping under load. If I accelerate slowly the car doesn't seem to do this. As mentioned the miss is every few seconds at idle. Otherwise the car idles smoothly. Sometimes it will start right up, then other times it will have to turn over several times before starting then act a little confused, bringing the rpm up to 2000 or so then down to normal and will smooth out. This car has always started right up so seems to be related to what I've described.
I've checked the plugs, wires, vacuum lines, pcv valve, fuel pressure regulator at least by removing the vacuum line and was dry. No smell of fuel anywhere. No SES. It has a new CPS, CTS, CSPS, fuel filter, 3 coil packs, all from previous repairs. Haven't tested the fuel pressure at the rail, but the pump sounds normal when priming. (?) Thanks in advance.

 

sure sounds like a bad plug or plug wire. have you done the dark test to look for sparks flyin. better do a vacuum test and compression test and test that fuel pressure just to take it out of the equation.

 

Thanks Craby. The plugs looked good. Didn't see any cracking, and I cleaned and gapped them. Not sure what else to look for there. They're delco platinums with about 40k on them. The wires are autolite pro series (something like that) and have the same miles on them. Haven't done the dark test. I'll do that once it stops raining here in Fl. We're not living up to being 'The Sunshine State' the last few days. Can I rule out a sensor with some confidence at this point since the car is running this way cold or hot, open and closed loop?

 

would be out of the ordinary for it to be a sensor. could be a sensor connection. get a buddy to finger all the wires while its running. lol. if he lights up theres a voltage leak.

 

Yeah really, lol. I was thinking possibly TPS. Guess it wouldn't hurt to test it. (with a meter) So can a plug fail internally? Like without any obvious fail on the outside ie cracks etc? What about the fuel evap canister solenoid. Any of those symptoms similar.

 

So I did the dark test. Only slight static up and down the plug wires, but only on the passenger side. There was an occasional very small arking from one of the plug wire boots, going to a heat shield that the boot was practically touching. What was most noted to me was static near the base of a plug, where the ceramic meets the metal. I can just see some of the ceramic out from the boot and there was static as the plug was firing. Normal? Also there was no miss at all tonight at idle while checking this out. The car was still hesitating and popping a bit at acceleration but mild. So should plug wires leak, lol?

 

Your wire(s) and/or boots are "leaking", shooting spark to ground, which will cause a miss. You need a new wire set.

 

Solved:

Looks like this was a case of weak wires, and perhaps a failing plug. I decided to replace the wires with a new set of Belden supreme from Napa. I had Autolite Pros on for about three years and thought they were ok, but after reading some not so good reviews and the suggestions here in the thread I decided to change them out. Wire for cylinder #3 was arking very slightly from the boot to the heat shield on the right side (passenger). And I was surprised to see the wire crack a bit and seemed to be just beginning to get brittle mid way down the wire, like it was heat damaged, but wasn't up against anything there. I noticed several months ago while chasing a separate miss problem (turned out to be failing coil) the wires got super hot. I mean you couldn't hold them for a second. High resistance? Beldens are designed for low resistance, at least thats the claim and so perhaps they'll do well. Also went ahead and took out the Delco platinum plugs that had about 40k on them, and went with the good old copper R43TSK. Which apparently provides better spark. The car accelerates smoothly and responsive once again, with a smooth idle. Wanted to note as well that the TPS was tested with a meter and read well throughout and and was seeing over 5 volts. Appreciate the responses and suggestions.