This past weekend i repalced the spark plugs, plug wires, and the air filter in my XJ. Started it this morning to go to work, and noticed that when it's idiling there is a very slight drop in RPM's (maybe like 100 or so) and a slight vibration. Any ideas on what that might be? It doesn't seem to be a huge deal, and still runs/ drives ok. But it didn't do that before, and am curious. Thanks for the help!

 

Sounds like you have a cylinder misfiring.

 

Hmm...could that be due to mis-routing the plugs? Although i did pay close attention to putting them exactly where they went, i don't think i routed them the EXACT same way.

 

Anyone know where I can find the correct routing of the spark plug wires?

 

AC compressor kicking on?

 

Huh? No the compressor is not kicking on.

 

Ok, was wondering since that's about a ~100RPM drop at idle when it kicks on. Sometimes people forget it's there.

Hm... ok, check the IAC on the throttle body to make sure it's clean and not gummed up?

 

Oh, ok. That makes sense...i was confused. No, i rarely use the AC. I got a new distributor cap, and found the routing in the FSM, now i will re-route all plugs and see if it goes away.

 

Ok, so i removed all plugs, replaced the distributor cap, and put all the plugs back in the right order (according to the FSM); however, it is still happening. It's feels like a slight vibration. This JUST started, since i replaced the plugs, and wires. Any more ideas?

I'm not saying that's not the problem, but wouldn't it be throwing a code and a CEL?

It also died, earlier today when i had it in reverse and was idiling. (if that helps at all). Although hasn't done it since.

 

Hm... what kind of plugs did you put in?

Did you check the IAC yet? Pull it out, clean it up, and slide it back in.

 

I put just basic champion copper plugs. Nothing fancy. The plugs are the BOSCH platnium plugs, because they were an entire dollar more per set then the duralast brand. I'll have to check the IAC.

 

Damn...i just posted this yesterday before 5, and it already made it all the way to the 5th page.

Update: So, i cleaned the IAC and the entire throttle body (it was really nasty) but it didn't help with the slight drop in RPM's. Is it something i need to worry about? The only thing that happens is there's a slight drop in RPM's and it's like a vibration i can feel in the brake pedal.

Any one else have any ideas?

 

Bumpity bump...anyone?

 

I figured it out! Finally!
Ok, so when i changed my injectors, the check engine light came on. I went to AutoZone to figure out what the problem was, it said cylinder 6 misfire. I checked the plug wire, and it wasn't on the plug very well. So, i snapped it back in place. Then the check engine light went away. Then, yesterday when i was driving to work the check engine light came on again. Took it to AutoZone, and same thing cylinder 6 misfire. Checked the plug wire, and it was on snug. So, i replaced just that plug wire for the time being. Took it home, and pulled the spark plug. It wasn't gapped correctly. I remember making sure all the plugs were gapped to the right amount, before i put them in. The only thing i can think of, is possibly when i was putting the plug in, i hit it against something (#6 cylinder is way in the back) and messed up the gap. So, now it runs great! No odd idle.

Long story, i know. But the point is i found the problem!

Quick question, will that slight misfire effect my gas mileage?

Thanks for everyones help.