Strange Noise/Vibration at Idle

[VoodooTTZ]

I searched for all things "Crank Angle Sensor" related, and found something similar to the problem I may be having, but it was never answered. So I thought I'd give it a try:

Engine: S13 SR20DET (Redtop w/fins) Fresh Rebuild

At idle, it will run fine, but if you rev it, as the revs come back down, there will be a brief noise/vibration. The best way I can describe it would be like if you had a plastic cylinder and a plastic piston and the piston was just ever so slightly smaller than the cylinder so that when you let it fall through the piston, it would cavitate and create a vibrating noise.

The noise seems to be coming from the Crank Angle Sensor area. If you barely touch the throttle cable sometimes you can get the engine to idle at just the right spot to make this noise occur pretty constantly.

I thought it might be the chain tensioner "cavitating" once the oil pressure came down when the engine slowed, but now i'm wondering if it isn't the crank angle sensor, as I was adjusting the timing tonight, and at certain spots it was making the noise, and was very noticeable through the CAS housing.

Is this something I need to worry about? Any help would be appreciated!

Thanks!
Modified by VoodooTTZ at 6:43 AM 3/23/2006

[180fan]

I think I know what you're talking about. Was your CAS sitting outside of the engine for a while?

[VoodooTTZ]

I believe so. The person I purchased this from had the car torn all apart down to the head and I think it sat for over a year. I completely replaced the Head and Block, and still had them hot tanked and all that good stuff, as well as anything else that went back into the engine I had it cleaned thoroughly.

The CAS I believe was sitting in a baggie with some oil still on it.

Am I doomed? DOOOMED! or does it just need to be pulled out and given a little lube luv?

Thanks.

[navysnail]

check things like your exhaust heat shields first before you start taking things apart. the fact that it vibrates at certain RPM's means that the engine is matching the frequency of whatever is vibrating.

[VoodooTTZ]

no heat shield. It's definitely internal and upper engine like in the valve cover...when adjusting the timing, if I advance it forward, the CAS vibrates and makes this noise. It's almost like a honking vibration, very nasal.

I'm also now having a problem with the idle, like it's missing, and it's backfiring (not loud CRACK backfire, rather a muffled FOOMP! backfire.)

The engine sits there and "wumwumwumwum<miss>wum<miss>wumwumwum WEEMWEEMWEEM wumwum<miss> <FOOOMP!> wumwum WEEMWEEMWEEM...etc. You get the idea. I'm stumped, I really didn't do anything between yesterday and today. It started doing this sporradically yesterday, but I thought that was because I had it timed incorrectly (thought it was to be timed to the second hash from the LEFT, when it's really the second hash from the RIGHT!) Timed it this evening, and i had a REAL hard time timing it, it didn't want to idle properly.

HELP!

[VoodooTTZ]

ok disregard rough idle comments above. I unplugged the #1 coil pack and no change, unplugged #2 and it got worse, #3 got worse, #4 got worse (obviously I didn't unplug all of them at the same time!) so it looks like I may have a bad coil pack :-(

Still curious about the noise the CAS is making?