PDA

View Full Version : Idle Vibration



Joisey Jim
02-03-2006, 10:51 AM
Just recently when my '94 SC is stopped but in Drive, there is some mild vibration and you can see the headlights flicker very slightly (I see it on the reflection on the garage wall) and the idle is around 600 rpm. As soon as I put it in neutral, the idle of course jumps back up to the stock 750rpm and the lights are stable. There are even ok when it's in Park. Do you think that maybe the regulator on the Alternator is poorly adjusted? Also the Alternator (a reman. unit replaced about 2 years ago) does have a harsh sound to it. I'm gonna pull the serpentine belt tonight and see if the alternator pulley rotates freely or is noisy. Any other idea's; could the trans be causing the idle to drop below the alternator set point.

RBH Racing
02-03-2006, 10:58 AM
I would look to a dirty throttle body or IAC valve/motor. Best thing that I have found to clean the IAC's is fresh gasoline. Brake or carb cleaner can have a bad effect on the plastic plunger. Just don't submerge the iac though, use the fuel on a brush or hold it as to only dunk the pintle end and not the motor. You can hang it off of something and let it soak for a while to let the gunk break up, then just swish it around and blow it out till it's clean.

Best thing for the throttle bore and plate is cat safe carb cleaner, and a rag on a screw driver. DON'T use a metal brush! A tooth brush or plastic scrub brush is fine.

quick35th
02-03-2006, 12:44 PM
Check your motor mounts. Most likely one or both are bad.

Shane

Joisey Jim
02-03-2006, 01:34 PM
Thanks Guys. I have solid motor mounts, but I never changed the trans mount - I can do that this week-end. I haven't cleaned the TB for ages either, so I'll try that too.

quick35th
02-03-2006, 01:48 PM
I have heard of some people breaking solid mounts before so you may just want to check just to make sure.

Shane

Joisey Jim
02-03-2006, 07:03 PM
The solid mounts and throttle body are fine. In Park or Neutral the idle is nice and smooth at around 750 rpm. It's only when I'm stopped in Drive that the idle is a bit lower at around 600rpm (always been that way); but the lights flicker a little, there is some mild vibration felt in the steering wheel, plus even the needle on the voltmeter waivers very slightly. I'm just wondering if their is either a problem with the trans. causing excess load on the engine at idle or the regulator on the alternator is faulting.

Capt.Trunks
02-03-2006, 07:11 PM
it sounds like your tranny mount my had the same problem about a week ago changed i changed the tranny mount and it stopped

RBH Racing
02-04-2006, 04:32 AM
The solid mounts and throttle body are fine. In Park or Neutral the idle is nice and smooth at around 750 rpm. It's only when I'm stopped in Drive that the idle is a bit lower at around 600rpm (always been that way); but the lights flicker a little, there is some mild vibration felt in the steering wheel, plus even the needle on the voltmeter waivers very slightly. I'm just wondering if their is either a problem with the trans. causing excess load on the engine at idle or the regulator on the alternator is faulting.

The guys are no doubt pretty knowledgable on this. Mounts go away on these cars all the time. With solid motor mounts it pushes more stress on the trans mount. Try revving and dropping in gear around 1500rpm(0 throttle) and see if you get the classic CLUNK!

This really sounds to me like a drivability issue. A weak plug or coil, bad wire or cross firing wire, something is letting your idle go low.
Although a diagnostic system is best, I think I remember in a thread in here that you can get the EECIV system to do a power balance test to measure cylinder contribution .

I think that you just have an issue that is letting your R's fall below the minumum amperage req. for voltage supply and it's kicking the voltage regulator. The flickering you are seeing is no doubt the bias between battery wattage and alternator supply.

Anybody remember how to test this out without a system?



Ray

Merlon
02-07-2006, 08:17 PM
mines was loose causing it to idle round 600-700.