I have seen a couple similar threads that had rough idles, but none that happened the same as mine or manifested in the same matter, so I just wanted to see if any other threads would be helpful to my situation, or if mine was different in some way, if so, if anyone could point me towards the right thread (or just tell me that any rough idle thread would help) I'd much appreciate it.

Anyways, my car recently developed a rough idle, the thing is, it only happens when the engine is warm. The idle starts to pulsate when I slow down to about 10 or 15 mph, also when I was idling around the parking lot trying to find a parking spot at school today.

It started happening after my dad and me replaced my battery (it's been having problems keeping a charge for a year now, I kept telling my dad it might be the alternator, but he was adimant that it was the battery, so far, he's been right, the battery keeps above the halfway point on the charge gauge on the dash, but we'll see in time). Anyways, we also replaced some vacuum lines that were damaged and were basically ripped. I don't know if they ripped because we were messing with the battery or not, but I do know that the one that connects to the ball (I'm assuming the vacuum) below the battery well, also behind the driver side turn signal, was not even connected because it also ripped. So we replace all the damaged lines and we also cleaned the connectors on the horns (because I've had a half working horn since I got the car going, but I'm beginning to think its because my warped steering wheel).

After we replaced the lines, cleaned the connectors, and put the new battery in, I took it for a drive, and it started right up, better than it did with the old battery. So I thought everything was fine. The next day I drove to work, (like a half mile drive), after I got off work and drove home, I forgot I needed something at work and drove back. That's when I noticed the problems starting to happen since the engine had warmed up. It started having a rough idle when I slowed down for the light. After I got what I needed from work I went to start my car and it started for like a second and then died. I tried to start it again and it just kept turning for like a minute until it finally started. Something I did notice was that when the RPMs got around 500 or so and the engine began to pulsate, when the RPMs would drop, so would the battery voltage level, like about as low as a quarter on the gauge.

Needless to say, I'm a little confused as to why my car is performing so bad all of a sudden. You'd think that if we repaired the vacuum lines that my car would perform better, not worse. I will say this, I did notice that the car did smell a tad on the rich side, but that might just be me thinking too much.

So yeah, any help would be appreciated.

Also, a back story for anyone who doesn't know, my car has it's original engine, and it has 255,000 miles on it, so there is that.

 

Have you been driving my car? You described my car's behavior better than I could. I have not found the answer yet. I will share it with you if I do. Good luck.

 

Forget relying on the dash gauge for your system volts. Use a REAL multimeter.

Here's a tip you should tell your father:

Bad batteries KILL alternators. Bad alternators KILL batteries.

Go to Autozone or somewhere and get the charging system tested. You probably have low system voltage when the engine speed is low, which means the alternator is weak or just about dead.

Also get a vacuum gauge on it so you know what you're looking at.

 

Where should we check the voltage? At the battery? Where should the vacuum be checked? I checked mine at the manifold. What vacuum readings are we looking for?

 

At the battery, in the lighter socket, wherever. Just get some accurate reading of the system voltage. You should be reading somewhere between 13.5 and 15V, usually about 14.7.

What vacuum reading did you get? Was it steady, or did it flutter? If it fluttered, did the reading flutter quickly or slowly?

 

I'll check the voltage. The alternator is suspect anyway. It seems to charge correctly but it makes a bit of a squeaking noise when it has a big load on it. The vacuum was about 15" Hg and steady.

 

Need to do an idle learn. The ECM lost that information when the battery was disconnected.

See the first three posts in this thread:

https://www.thirdgen.org/forums/v6/1...dle-learn.html

Talks about how to do an idle learn and cleaning the throttle body (TB). The EGR dumps in right behind the TB which coats it and the throttle blade in carbon.

RBob.

 

I didn't read everything but if you suspect the alternator get a hold of a couple of banana plugs, some wire, and a cig lighter adapter and make up a test lead to plug into the cig lighter socket. Then you can watch the voltage in real time while you're driving around. Mine tested fine and I was stumped until I tested it while driving around.

I can tell you from experience that from what I read it does sound like it could be the alternator, but it's good to know what the voltages are before hand so you know if any changes makes a difference. Also, the fact that it gets worse after it warms up would be consistent with the alternator because heat can cause electrical issues to worsen.

Try that idle re-learn first though since it's free.

 

Thanks for all the replies guys. I'll try the idle learn thing first since I don't know if I have the tool to do a vacuum check (I'll ask my dad if he has anything of the sort), since it (to me) seems like the most likely thing. Because like I said the car didn't do what it's been doing beforehand. If it isn't that, then it very well may be the alternator (in which I can say I told you so to my dad). Either way, thanks again for the replies. I'll post back once I've tried the idle learn thing tomorrow.

 

I've actually run into a problem. The idle learn process talks about waiting for the fan to turn on. Thing is, we have my fan wired to be on all the time since it never came on and caused the car to overheat. What would I do in the process then if that's the case?

 

Fix your fan, either a bad relay or bad fan switch.

You can also put a paper clip between terminals A and B on the OBD I connector and wait for it to slowly blink (closed loop).

 

Alright, I'll try that this weekend. Thanks.

 

Alright we got it to work and my car is back to normal, thanks everyone for all your replies.

 

If you wouldnt mind, could you post what you did to clear the issue up? Just for the other members of the board having the same/similar problems.