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View Full Version : variable RPM at idle, battery drain



Jacob
08-05-2003, 08:10 PM
Here's maybe a challenge for you T-bird whizzes......MY 89 t-bird was driving perfect until we had A/C fixed, now the idle falls low slightly under 500 then kicks up to 1000, then falls back down to 500 repeatedly, running rough at 500 like it wants to die - any suggestions how to fix this?

After I got the A/C fixed, the plastic clip holding the line attatched to the throttle body had come off during the repair, causing the tranny clutch to wear out, so we had to put it in a shop to fix the tranny, when it came out it either still had the idle problem or that's when it got developed, not sure which.

Also, it did this for awhile, I drove anyway, but then after sitting a little while, the battery ran dead. I recharged existing battery, put a new one in, ran it, and then parked making sure nothing was on and the next morning it was dead again. The battery thing may or may not be related to the above idle problem - it had the automatic transmission rebuild not sure whether the idle problem developed after the rebuild or before, but definitely after the A/C got fixed. Also, the battery problem didn't happen till later so I think it may be a separate issue.

Are there any tests using a voltmeter I could do to find where the battery drain is, and/or whether the alternator needs replacing?

Any help would be appreciated.

Thanks,

Jacob

Aaron Pedroza
08-05-2003, 10:14 PM
Well, let's see. The idle thing may be IAC valve on TB or possibly even the TPS. Check that out. The battery thing is probably either the battery dead, charge and do a load test, or you have a drain on the battery somewhere. Usually checking codes would tell you that, my fuel pump relay went out and it drained my battery before. Have heard of an ABS relay that can do that too but you would hear that. Biggest thing is check for codes with electrical. Try not to relate any problem with fixes you have done, doesn't sound like they are related.

Just a thought, have you grounded out anything while doing work on your car? Could have pure electrical problems due to frying relays.

MIKE 38sc
08-06-2003, 12:56 AM
If the diodes in the alternator go out it will cause your battery to drain down by letting current flow backwards through the alternator when the car is shut off and parked. I've even had that bad alternator cause the idle on the car to drop like that.
Could be 2 different problems like Aaron says or it could just be the alternator. I'd check the alternator first and see if thats your problem, then take it from there.
Any Auto Zone will check it for free. Just take the alternator off and take it to them.



Edit: I forgot to tell you to remove the posative battery cable BEFORE you work on the alternator wiring, if you dont and accidentaly short to ground the ~~~ terminal on the alternator you WILL burn up the diodes IF they already arent.

Jacob
08-06-2003, 02:23 AM
Thanks for the tips, This will get me started. Will keep ya'll posted

Jacob

TbirdSCFan
08-06-2003, 02:55 AM
Originally posted by MIKE 38sc
If the diodes in the alternator go out it will cause your battery to drain down by letting current flow backwards through the alternator when the car is shut off and parked. I've even had that bad alternator cause the idle on the car to drop like that.

Any Auto Zone will check it for free. Just take the alternator off and take it to them.

Edit: I forgot to tell you to remove the posative battery cable BEFORE you work on the alternator wiring, if you dont and accidentaly short to ground the ~~~ terminal on the alternator you WILL burn up the diodes IF they already arent. Ditto on the alternator. Mine went out and drained the battery. Beware of Autozone alts. It took 3 of them before I got a good one. Also, be sure to fully charge the battery first with a trickle charger before you use a new alternator. Check it with a bulb or bead type battery tester. When the car is running off the battery, and it drains it, all sorts of wierd things can happen.
Clean the batery posts and clamps and check the voltage across the batt terminals at idle, should be about 14V.

TbirdSCFan
08-06-2003, 03:01 AM
Check your engine mounts also. Collapsed mounts were the source of my idle problem and it was much like you described whenever I used the A/C. If your oil filter is almost touching the frame, the engine is probably resting on the subframe. This is bad for your power steering lines, and oil pan, but also causes a low idle due to the knock sensor picking up noise from the metal to metal contact. The EEC retards the timing, hence the stumble. You probably have some unknown vibration when sitting at a stop light in gear too I'll bet. ;)

Joisey Jim
08-06-2003, 02:07 PM
Same thing just happened to me; although my battery light did come on first, then the idle was erractic. I switched batteries with my '93 just to make sure it wasn't the battery and, ended up buying a remanufactured alternator because the regulators are internal & can't be checked or repaired easily. Auto Zone didn't have one locally, Advanced Auto needed a day to get one in & good old PepBoys had one in stock for $139. Then getting the old alternator out is no fun, as it involves removing the top intercooler pipe (need the special teflon tape & 148 lb torque wrench - luckily I have both) plus taking off the coil pack to release the rear bracket and then my intercooler fan, to be able to withdraw the long bottom bolt. Charged-up the battery and for 2 more days the initial idle was like s...., now it's ok - maybe an EEC relearn issue !!!!
Happy motoring,
Jim.

Jacob
08-06-2003, 03:39 PM
Alternator tests out ok.

I was also told someone saw the battery light under the dash come on/flicker or whatever its supposed to do, but yet no alt. problem

Didn't think of the motor mount........could be although the oil filter doesn't quite rest on the frame. Have to jack car up and check for certain. Keep everyone posted

thanks,

Jacob

Jacob
08-06-2003, 03:48 PM
Re: Aaron Pendroza's comments:

How does one "check out" the IAC valve, TB, or TBS? TB looks fine and anyways can't cause the fluctuation to my knowledge.
Also, the ABS doesn't work at all, so it cooould be that relay, though I have no way to be sure.......is it possible to just disable the relay or something?

Yeah, I'll have to get a code test ran prob'ly

I keep thinking about how the idle started getting eratic after I fixed the leak on my A/C, is there anything sensitive back where the lines run into the firewall that could have been knocked, bumped, etc. which would cause all these idle problems? After all, the Auto Transmission burned out just because the guy helping me broke the clip connecting the TB to one of the lines. Maybe he did more than that.......

Note: Work not on touchy cars when slightly intoxicated.

lata

Jacob