Engine Vibrations

[Shazam]

Car: 1996 900 SE, Autobox

Problem: So on a short drive back home, I noticed my engine started vibrating a lot when I was coming to stop signs. It usually happened once I got below 10 mph, and the RPMs were ~1000, but once the shuttering/vibrating started, the RPMs would dip to about ~800. Once stopped, the vibration usually quickly stopped as well, and the RPMs returned to their regular ~1000+ range. Guys think it's the automatic transmission starting to go? Shifts seem regular, although it does seem to take an extra little time to go from R to D.

[Burnsside42]

Ever try and flush the trans? Best thing for an automatic trans it to keep the fluid looking new. Once it get's dark - it's all downhill....

RPM signal could be weak - if the CPS is going bad it could cause the engine to perform oddly at low RPM's - has it ever had "hard starts" with extended cranking?

[Shazam]

Haven't flushed the trans fluid yet, but I believe the PO did, and I've only driven it less than 30,000 miles since (over three years). And yes, the car lately has been taking a bit longer to start, but it got slightly better when I just replaced a leaky fuel filter (about four days ago). I contributed the hard starts to driving the car less than once a week, and the drives all being within 10 miles in the past two months (don't drive much in college). Either way, I'm going home next weekend, should I fear my car won't make it home? And will I be able to fix/do something about it there (I know I can change the AT fluid, or at least do one flush).

[Burnsside42]

Trans flush/change fluid is always good preventative maint.

As long as the car starts it will drive more then likely. I take it you have not had any CEL come on yet? This would indicate the fault is not in the ignition directly (aka DI or Plugs) I would take a few minutes and just look around under the hood. Be certain all vac. lines are hooked up properly and that they are not dry rotted or broken. A common issue I've seen on the T5 900's is that the idle air control valve or IAC - can get rather dirty from years of driving and a nice cleaning can often rectify a poor idle symptom. Warm-Hot water and some electronics cleaner work wonders.

[Shazam]

Not CELs yet. Last time I was under the hood, I didn't see any rotted or disconnected vacuum lines, but I wasn't particularly looking for any. I'll give those a look-see. I replaced one or two of those this summer that looked like they might give me some trouble, over the summer. Also, where is the IAC, I'll have to check that out too if possible.

[Burnsside42]

Passenger's side - top of the intake manifold - mess of large hoses going to a metal cylinder with a connector.

[Shazam]

Went out to the car, all the hoses seem in good condition and attached well, I just gave every wire I could put my hands on a good snug-push, and now it's not doing it... hmmmm. I don't think any thing I did really could have done anything. I think I'm going to do a ATF change, and clean the IAC. Is it safe to just disconnect everything from the IAC to remove it, and then give it a cleaning?

What ATF is recommended for a 1996 900?

[Burnsside42]

Yes for the disconnect - like I said before for cleaning. What I used to do was use very little soap and warm-hot water to clean it out and loosen things up. I would dry it by shaking it about a bit then spray some electronics cleaner in it to ensure all the water is cleaned out and all the loose carbon bits come out. Once it's dry put a little dielectric grease on the connector and re-install. This USUALLY would fix them for awhile, sometimes permenantly.

As for ATF - Regular ATF is all you need. Nothing synthetic or fancy.

[IAmTodd]

With the age and I'm sure quite a few miles I would avoid a power flush in the trans. It will dislodge the junk and end up causing more damage in the long run. Either disconnect the cooler lines and let it pump out the old fluid while you power in new fluid at a similar rate or drain as much from the drain plug and refill. Repeat until you your fluid is bright red.

[Shazam]

Yes for the disconnect - like I said before for cleaning. What I used to do was use very little soap and warm-hot water to clean it out and loosen things up. I would dry it by shaking it about a bit then spray some electronics cleaner in it to ensure all the water is cleaned out and all the loose carbon bits come out. Once it's dry put a little dielectric grease on the connector and re-install.

So are you saying it's okay to submerse it underwater?

With the age and I'm sure quite a few miles I would avoid a power flush in the trans. It will dislodge the junk and end up causing more damage in the long run. Either disconnect the cooler lines and let it pump out the old fluid while you power in new fluid at a similar rate or drain as much from the drain plug and refill. Repeat until you your fluid is bright red.

I thought it went drain old. Put in fresh. Drive it around for a hundred miles or so, or after a couple days. Drain. Put in fresh. Drive around again... drain, and fresh for the last time. My Haynes says to just drain it, and then top it off with new and then your good for another 80k miles. What do I do?