96 SR: Little bit of a rough idle, what to check?

[mike5]

The car drives great and the engine is overall very smooth. As far as I can tell power is great as well. But at idle, it feels a little rough. I don't want to make it sound terrible, but it doesn't feel quite right to me. It almost feels like constant misfires, but I don't think that to be the case as the car is OBDII and it would throw a check engine light. Basically at idle you feel light vibrations. But I have no problems accelerating from a stop or anything like that. I had my mechanic check the plugs and he says there are the correct ones and in good shape.

Assuming the plugs are ok, what else can I check? I thought I'd read something about coil packs or boots to them. Is that right? Should I be checking those?

Any help would be appreciated.

 

[zukrider]

its very common for older v6's to slightly stumble. its a design flaw. honda first gen v6's do it, isuzu v6 does it, my 94 sr does it. i wouldnt worry, but you can always get it checked out.

 

[mike5]

Thank you sir for the feedback. My family has owned V6 Toyota sedans for 15 years and they've all been pretty smooth from what I could remember. But if you experience it and have heard of others (along with no CE light on my OBD2 car) then I'm good with that!

Thanks again,
Mike

 

[off-roader]

Not sure what Zuk is talking about but I've owned over a dozen v6's w/ over 200k and none of them stumble unless somethings wrong. Usually ignition or fuel related. Sometimes it's engine management.

How old are the plugs and what type are they? I can only recommend NGK or Denso (NipponDenso) iridium plugs. All others will not last nearly long enough.

Did he check all 6 or just a couple of plugs. If he checked all six then he should have just replaced them all since one of them is such a pain to access where most mechanics will remove your intake just to access it and this is far from a minor undertaking.

Also did he inspect the wires? Then there's the MAF sensor? Of course poor fuel or a malfunctioning fuel pump or fuel filter can also cause stumbling symptoms.

 

[mike5]

The car is with my mechanic now. From what the mechanic said, they've checked the plugs on one side, and they looked correct and good. They will be checking the other side (the more difficult side) this coming week. I've asked them to replace the fuel filter. I've also asked them to inspect the ignition system. I'm not sure how the setup works in these cars. I don't think it has coils on each cylinder, but again I don't know what the setup is. If there are wires, then maybe it is worth replacing them. Also, I know with coil packs sometimes the plastic tube that goes down to the plug wears out and that creates problems. I guess I'll find out from my mechanic.

I wouldn't say the car is stumbling, but you can feel a slight vibration at idle. If it is the MAF, I would expect issues through the rev range or really poor mileage. also, all I have to do is disconnect the MAF harness.

 

[zukrider]

its what he said, a "slight" vibe. and i bet its sporatic as well. 90% of people dont even realize its there. but the other 10% are the ones that are either fanatical, sensitive, or so unaware of how cars work, there paranoid.

i used to be a mechanic, and never noticed until li had to "diagnose" it. if it is what i interpret it to be, its normal. but offroader's suggestions are good for an actual issue. id lean towards fuel quality first, then ignition system!

 

[off-roader]

its what he said, a "slight" vibe. and i bet its sporatic as well. 90% of people dont even realize its there. but the other 10% are the ones that are either fanatical, sensitive, or so unaware of how cars work, there paranoid.

i used to be a mechanic, and never noticed until li had to "diagnose" it. if it is what i interpret it to be, its normal. but offroader's suggestions are good for an actual issue. id lean towards fuel quality first, then ignition system!

That's pretty interesting. I hadn't heard of it before but as the saying goes "You learn something new..." right? Any online info/documentation on this? I want to ask some of the other Montero owners I correspond with about it as well to learn more. Piqued my curiosity... you know what I mean?

 

[zukrider]

no material on my end. like i said, most people dont notice, because it is so slight. generally, the ones that do, are the type to only use a mechanic. and its so few and far between, that its not a common issue brought up. out of shop at least.