Idle shaking

[shojoe1997]

I have a 98 SHO with 83,*** miles on it, when I am at idle the car goes from its normal 700-800 idle RPM to 500-600 and it starts to shake and feels as if t were staul. No engine lite or anything, can someone tell me what it might be?

-Joe

 

[stephen newberg]

Does it drive normally otherwise? Are the cam sprockets welded?

pax, smn

 

[shojoe1997]

Ya, it's had tranny problems but an undercarriage wash and fluid fixed that, also in the past it's had spark plug issues and misfires, cams have been welded since I bought it in '99, but AT THE MOMENT all 8 cylinders are working, no lights on, it's just a shake an lowering revs

-Joe

 

[stephen newberg]

OK, sounds like the idle air control sensor, perhaps. They get dirty. Sometimes you can successfully clean them, but sometimes you just have to put in another. IIRC, they are not expensive.

pax, smn

 

[shojoe1997]

It did have a bad oil leak a few years back, it still smells alittle when the engine heats up, so could the oil be what made it dirty?

 

[jimtash]

I get that too sometimes and heat has a lot to do with it. Does it do it after it's been driven for a while or does it happen all the time?

 

[shojoe1997]

It starts to do it after a minute or two. I saw your question so I started it and sat in it, and halfway through the first song it started to shake, could it be what Stephen Newberg (person who commented before you), the idle air control sensor? It only has 83k on it, it has had a oil leak AND a coolent leak, so there is probably crap baked in the sensor

 

[jimtash]

The sensor get carboned up from normal use. You might have a weak coil as well. My '98 has 77,000 miles and one crapped out on me a while back. And before it finally gave out, I experienced the same thing that you are but it recovered to its normal idle after a few seconds.

 

[shojoe1997]

That's what mine does, it feels like it is going to stall, but then it goes back. Could you tell me what you had to replace and where you can get them, or if it's just an easy piece to get. I don't need a step by step, just what you fixed

Thanks
-Joe

 

[jimtash]

I replaced all the coils. You can find an entire set on Ebay for a $100.00. The rear bank is the one that gets the most stress simply from the heat produced. And with coils they not only deal with that, but wear out over time from use.

I forget to add that if you replace the coils, install new plugs in there as well. The gaps on some of the original plugs had worn over 15% from stock. That alone puts extra stress on the coils as well.

 

[shojoe1997]

Ok Thanks for all your help, Ill order the stuff then after Sandy Ill get working.

Thanks Joe

 

[stephen newberg]

If you are not getting a code indicating a misfire due to plug or coil, it could be just a weak one. Certainly you can replace them all. I suggest trying the idle air control sensor first, as the miles you are at it is a very likely problem regardless, if it has not yet been cleaned or replaced. The coils in each plug socket often go a lot longer than 70-80K, though some of them start causing problems that soon. My first one did not start to go until 190k or so. It varies a lot.

But if you have had oil leakage and any of it got into the air system, I would certainly take a look at the idle air control sensor first.

pax, smn

 

[jimtash]

Mine did toss out a bank 1 misfire code along with a dead cylinder because of the coil finally giving out. And the weird thing about it was this happened about 2 months after I replaced the plugs.

Still a good idea to either replace the back 4 coils or at least rotate them front to back and change the plugs out. The ones in mine had gaps as high as 0.055 with just 70K miles on them. That will also put a lot of stress on the coils.

 

[stephen newberg]

Actually, I think it is common for a coil to die shortly after changing plugs. For some reason, after they get old, they do not like to be moved about much. I have heard this reported often, though I do not know if there is a firm reason why. Micro-cracks getting larger when moved, maybe?

pax, smn

 

[shojoe1997]

Ok. thanks, i havent really gotten the chance to take it to a place to get the code checked due to preperation for sandy, I had to get my 89 and 92 in the driveway with a car cover, I just had a misfire last year and i dont think it is one of them agian, ill check the idle air control you said about.
Thank you for your help Stephen
-Joe

 

[shojoe1997]

Ok thank you, now that Sandy is gone, i can take it somewhere to have the codes checked out and get it fixed

Thanks
Joe

 

[stephen newberg]

Excellent. Hope it all works out.

pax, smn

 

[alecracing]

If the engine light is not on there will most likely be no code.

Cheapest thing first, clean the throttle body. If its still messing up, tap the idle air control valve and see if engine idle changes. I had a Ford truck that ran fine for a while then started having idling problems, took off EGR valve and cleaned and solved the problem.

Also, I rotated my coils and engine ran fine for a day and then started stubbling BADLY after running 5 minutes. Code for MAF came up. The coil I rotated to cylinder #8 was bad and messing with the MAF sensor somehow. Maybe feedback or electromagnetic field or something. swapped 7 and 8 coil and fixed it. I replaced all the coils anyway.