low idle miss

[1FST ZR-1]

Trying to decide on what to change first. Car has 60k on and gets driven like it should, it has a low idle miss that is noticable from the exhaust note.I drove it from Redding ca to LA and back and averaged 28 mpg with a few120mph blast so it seems to be in tune. I had a good backfire a while ago so I thought it may have a vacuum leak under the plenum, so after a quick plenum pull all was well. It has rc injectors and the stock wires and coils. I did notice that when I pulled the #2 plug wire the rpm did not seem to change so I pulled the #1 plug wire and it seemed to do the same,(no change in rpm). But each plug wire was firing after i pulled them off so does that mean the coil pack is ok or can it be weak? I mean other than the very slight low idle miss it pulls just as hard as ever. Anyway I have done a quick fuel pressure check and both pumps are good and the injectors are holding pressure and it always starts hot or cold. So any thing to check plenum on or off? Thanks for any help.

[Jeffvette]

How was the spark when you pulled the plug wire off?

[GOLDCYLON]

How was the spark when you pulled the plug wire off?


Hmm coil packs?

[Jeffvette]

Hmm coil packs?

Yep, if the coils are strong, you will be getting an audible snap when it fires. Weak ones will die out within a half inch or less from being disconnected.

[1FST ZR-1]

How was the spark when you pulled the plug wire off?
Hey Jeff, The spark was snappy and when I grounded it the spark was constant and thick so to me it seemed ok. When I pulled off the wires for 1 &2 I swear the rpm didnt changed and I really expected to hear the flywheel start to rattle from the miss but it didnt. Maybe I should change the plugs they have about 10k and the gap is at .032-.035. thanks.

[Paul Workman]

Well...

Mine sometimes does something that sounds very much like what you describe: Only at low idle, when cold, more often if it has been idling for some time (as in idling until it gets warm), never noticed it if the idle is hovering closer to 1000, almost never after it has finished a romp or two along some deserted blacktop.

Like you, my mileage on the flat in cruise is 26-28 at 70mph or a little over, pulls like a 'beast' with the hammer down. I'm curious too, but there are other things I want to focus on - like a vibration - so that niggling little low idle "tick" will have to wait. Always something to putter with, huh?

But, back to your quest...

If the spark is eliminated, I would be curious to see what a vacuum gauge would tell me. A leaking valve would cause the gauge needle to "tick" (lower vacuum) in rhythm with the revolutions.

That being OK, (whew) then I would be wanting to check the resistance of the suspected injector coil(s). 12Ω Â± 1 Ω, according to my FSM is OK. 9Ω or less is a sign the coil is breaking down and the miss my be due to an injector.

Then, a compression check might shed some light on the path.

Do keep us informed!

P.

[32valvZ]

My vote is for plugs & wires.....since you seem to have no fuel issues. By the time you pull the plenum to ohm the wires, you just may as well put in a new set.