Originally posted this in the 3 Door Coupes forum. I copied it to here for (hopefully) more input:

Hello,

Just picked up a 2000 SC1 for a daily commuter. Has SOHC & 5 speed. Run's and drives out very nice. But there are a few things I'm curious about.

First, in the morning after warming up for a bit the RPM's are about 900 +/- . Then taking off down the road and up shifting the RPM's stay at about 2000 for a second or so after letting off the gas pedal. They will drop if I coast. No problems after several miles and all warmed up. When warm and coming to a complete stop, RPM's stay at 1200 for a couple seconds or so than drop to 800 +/-. Is this normal?

Second, at highway speeds (60+) there is a very high frequency vibration. Almost unnoticable except that the rearview mirror makes the image slightly blurry and can barely feel it in the wheel and shifter.I don't think it's wheel, tire or suspension related. Perhaps something in the driveline? I had a similar experience in my Mercedes that turned out to be a driveshaft flexdisk that was bad. I'm guessing this car has no such thing, but perhaps worn subframe or motor mounts (Mercedes experience too)? Or is this normal?

Lastly, all electrical related stuff appears to work just fine. No blown fuses, dimming lights, etc. Again at highway speeds there's a sound coming from the dash/console area. Almost sounds like a solenoid clicking. It's not continous, happens at random, not casued by road surface conditions and makes no difference what (if any) electrical things are operating. Any ideas?

I realize I've got an old car with a lot of miles, and some of these things mentioned might be SOP. But if something is giving me a heads up of a potential issue, I'd like to nip it in the bud.

Thanks,

Cliff



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Update:

Seem to have traced high freq vibe to a well worn upper engine mount. Replaced it and things are much better.

Dash clicking sound was traced to a loose radio. The two screws were not tightened down. Was told by seller radio was recently replced. A simple fix.

Haven't investigated the (seemingly) high idle. Any suggestions??

Cliff

 

1. The RPM's staying up i guess would depend on how long they stay there. Does it sound like the clutch is slipping. It might just be worn, or just cold. Does it do it after driving around? I dont think the rpms staying at 1200 when comming to a stop it anything to worry about.

2. Almost all vibrations at high speeds are going to have to do with tires, wheels, or brakes. Try and see if you go about 70 and let off the gas and just coast. If it doesnt really go away then its nothing to do with the motor mounts. (which i cant really see it being anyway). Then try and go 70 and hit the brake a bit and see if it goes away. My guess is its one of a few things. A loose lug nut, which is easy to check. Or just the wheels arent balanced correctly

 

Clutch has a good feel and will kill engine if in gear and engaged slowly. After two weeks of driving I've learned a few things about how the engine behaves. I believe all is well in the warm-up period. RPM's stay a little high until coolant temp comes up. But after 15 miles and coming to a stop, if I take out of gear and coast (no matter the distance) it stays at about 1200 rpm until car is completely stopped and then after about 4 seconds it will drop to about 850 rpm. Probably nothing to worry about really.


As to the vibe, the motor mount cured that. Front brakes & rotors are new and tires were balanced just before I bought it. No doubt wheels and brakes can acount for many vibrations. But experience told me to look past the obvious based on the type and feel of the vibration.

Cliff

 

Cool. Sounds good. Glad you figured it out. Thats the tough thing about trying to diagnose stuff over the internet is that we cannot feel it or hear it so stuff like that is really hard to determine, which is why i usually state the obvious first.