Hey, my 96 XJ has always run great as long as I've had her, except for the slight vibration every few seconds at idle. I did a tune up last summer and I honestly don't remember if it existed before the tune up. What would make me think this is that I stripped one if the screw holes for the distributor cap when installing it, and it sits slightly lopsided. Should I see what cylinders plug wires are on the part of the cap that is "higher up" (not screwed down tightly) then maybe remove the plug wires for the cylinders one by one and check if it improves? I usually don't say I'm good at things even if I really am, but I do know what I'm doing with cars. But I've never had a problem like this before, so should I disconnect the plug wires one at a time and see what improves idle? Sorry I wrote way too much, I over explained it...
Thanks,
pdowty68

 

Vibration as in...? An RPM fluctuation?

 

If you stripped one of the screws for the cap that could be your problem. this would cause the cap to sit lop sided like you said, and would reduce the energy going to the plugs on the side that is up in the air a little. I would look at the were the cap mounts and see if you could tap a larger screw in there. maybe some one else can chime in but that's what I would do.

 

yes but very slight, you can't even really see the tach move when it happens, I hope it's a simple spark problem. I hope it's not a fuel delivery problem. But I think I have leaky injectors or need a check valve, because after it sits for a while, it takes a lot longer to start. I crank for about a second, stop, then crank again and she starts right up. If I wet to shut her off, then start her right away again, she starts in a half second of cranking. It's embarrassing when I have to crank twice like that. Is that most likely leaky injectors?
Thanks guys

 

Subbed for figuring out the cranking issue. I'm having the same problem

 

right? Isn't it so embarrassing? I want to fix it really bad, but I really want to fix it before I put nice exhaust on her. Because then everyone will hear it even more... What happens with leaky injectors is that the fuel rail looses pressure and the fuel pressure has to be built up sufficiently again before she will start.

 

maybe I'll try pressing down on the cap while she's running, and see if it stops

 

And sorry to put the injector and spark issue in one thread, I should've kept it separate....

 

Very embarrassing haha. Sometimes it will crank on first try in the morning but not often

 

do you have your heater on defrost when this happens?

 

If you have 'vibration' and see the rpm's decrease every few seconds, a few things to check.

Is your A/C on when this happens? The e-fan will cycle when A/c is on, causing a slight drop in rpm's in some, that goes accompanied by the sensation of vibration. This repeats itself in almost steady intervals.

When the vibration/irregular idle occurs, its always worth cleaning your IAC and throttle body. It's a good maintenance cleaning item, and esp if idle is getting rough (your slight vibration at idle might be the start of that, give it a clean.

Another thing worth checking is, if your harmonic balancer isn't on the way out. with the engine running, check for wobble and check if it hasn't been migrating forward.

for completeness you mighht want to check for codes (or for starters if you want), to make sure it hasn't stored any codes relating to misfire.

See how you go with this.

 

I had the same crank issue with my '98. When I put my 703 injectors in, the problem went away. However, I still have a slight stumble at idle. Only at idle though. I've done a full tune-up and TB cleaning and just about everything else. I think it's just the nature of the beast. It runs great otherwise so I'll just let it be.

 

Yeah if I put my hand anywhere on the engine, I can feel this vibration, I'm still gonna clean the IAC, but if you unplug it and it still does it then it's not the main cause (well id assume) I have the symptoms of leaky injectors as described above so I guess swapping out my injectors would likely fix two problems.

 

Cleaned my iac and still had the same problem

 

pdowty, I would suggest you check your fuel pressure and make sure it is within spec. My fuel pump isn't the best, and the sending unit is shot, so I think a lack of total pressure or consistency of fuel delivery from the pump may be the cause of my slight idle stumble. It would be wise to check pressure and rule that out as a cause.

My starting issue went away with the new injectors totally, hasn't happened since. I think what happens with a leaky injector is that if you don't smell fuel anywhere, it can actually leak down into the cylinder. I believe this is what was happening with my old injectors.

Also you should still be thinking about the check valve in the fuel pump module. This valve is supposed to hold fuel pressure in the lines when not running. If this is faulty, it will all leak back to the gas tank, causing a longer/harder start. One way to check for this is the "poor man's prime":

1. Turn key to ignition until you hear the fuel pump run.
2. Turn off when you hear the pump stop.
3. Repeat 3 times.

If it starts right up then, you could have a leaky check valve. The problem I had with this test is that the hard starts just weren't consistent for me. I think I ruled this issue out when I put my new injectors in and the problem went away.