I am a new Mark viii owner and new to this message board. I am not super smart on cars in general, but do have some knowledge. I've wanted a Mark viii since they came out in 93 and I just now got one. I have a '94 with 76k miles. Ok, now on to the question.... Once in a while after I have "got on it" my car starts to idle rough (thats the best way I can describe it). The tac wil bounce between 500 and about 800 or 900 if I remember right. What do you guys think this is? My first though was that it is some kind of valve sticking, but I have no idea where to start. Any help would be great.

ok,what i think you are talking about is a rolling idle. have you checked for vacume leaks.you take a can of B-12 and spray around the intake and vacume hoses.be careful not to spray it on the exhaust manifolds,if you hear the engine smooth out , focus on that area for a leak. a idle air controlvalve dosnt seem likely,because they are an actuator that does what its told, on the other hand it cant tell on itself unless it is shorted or open.also, check the mass air sensor that is located in the air filter housing.sometimes thay get debrise on the heated wires and cause the car to idle funny. id love to show you pictures of these parts and there location. but i bet there are a few guys with all the stuff i missed. welome and you came to the right place.keep us informed .

It could be a couple of things. It could be the vacuum leak as described above, but if it was you would have it more at WOT than at idle. It could also be the debris on the mass air, but I am not sure about that. It is possible....stranger things have been known to happen. It could be that you have a sticking IRMC, and to fix that you can use some Sea Foam to clean it up. What happens is that you can get SO much carbon build up that when it opens at WOT it sticks open and you get the stumbling at idle. Cleaning up the carbon will allow them to operate properly in the full range of motion and could fix your problem. It could also be that simply need to change the spark plugs/wires. Mine did the EXACT same thing a while ago. It ran fine at higher RPM's, but at idle it was rough to say the least. I replaced the plugs/wires and it was all good.

Hope that helps a bit. :Beer

Clean MAF, check IAC.

Well, I've got several things to try now. Thanks for the help, I'll let you know how it turns out.

Clean MAF, check IAC.
What is the proper way of cleaning the MAF?

i would try a q-tip and some alcohol.most people i know just use b-12

i would try a q-tip and some alcohol.most people i know just use b-12

NO! Do not use alcohol or q-tips, they WILL damage the MAF and you'll have to buy a new one!! Simply purchase a can of quck-drying electrical contact cleaner ($1.99 @ AutoZone) and spray the hell out of it until the sensors are bright and shiny metal.

dosent the product you are talking about have alcohol in it.the end result is the fact that you dont want any oiley residue left on the sensor.ive sucsefuly cleaned hundreds of mafs and not hurt any of them.if the sensor is bad its bad . no cleaning will help.

No alcohol in it. It's something else and leaves no oil or residue that can clog or damage the sensors...

I have heard of seafoam in the past, but I recently had my oil changed and I asked about it. The mech had no idea what I was talking about. where can I get some, how is it used, and please refresh my memory, how dose it work.

I have heard of seafoam in the past, but I recently had my oil changed and I asked about it. The mech had no idea what I was talking about. where can I get some, how is it used, and please refresh my memory, how dose it work.

$5 at AutoZone. You can put it in the tank, the crankcase, or through the pcv/ brake intake valve...

$5 at AutoZone. You can put it in the tank, the crankcase, or through the pcv/ brake intake valve...
Thanks for the info!

:headbang: You got it, boss!

It could be a couple of things. It could be the vacuum leak as described above, but if it was you would have it more at WOT than at idle. It could also be the debris on the mass air, but I am not sure about that. It is possible....stranger things have been known to happen. It could be that you have a sticking IRMC, and to fix that you can use some Sea Foam to clean it up. What happens is that you can get SO much carbon build up that when it opens at WOT it sticks open and you get the stumbling at idle. Cleaning up the carbon will allow them to operate properly in the full range of motion and could fix your problem. It could also be that simply need to change the spark plugs/wires. Mine did the EXACT same thing a while ago. It ran fine at higher RPM's, but at idle it was rough to say the least. I replaced the plugs/wires and it was all good.

Hope that helps a bit. :Beer

Ok, I'm not sure what IRMC stands for, I'm assuming that WOT is (wide open throttle). May sound funny, but I was wondering if there is some kind of glossery for those of us new to this? Maybe a link to common abrebiations that get used in this forum. Sorry, but I'm new...... but anxious to learn.

Intake
Manifold
Runner
Controller

Here's a picture: