My 98 is misfiring intermittently at idle, but no CEL or any codes. When I rev it in neutral the response is delayed and the rpms go up slow. Any ideas? I cleaned the mass air sensor today but it didn't seem to help.
98 LSC misfire?
- Thread starter 98LSC32V
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MonsterMark
Dedicated LVC Member
IAC? Idle Air Control Valve. This can certainly cause your symtoms.
Cylinder balance test would be nice also to check the coils but a can of Seafoam thru the PCV wouldn't hurt things to clear out some carbon.
IAC is about $60 and easy to replace yourself on a Superior 2nd Gen Mark VIII.
Cylinder balance test would be nice also to check the coils but a can of Seafoam thru the PCV wouldn't hurt things to clear out some carbon.
IAC is about $60 and easy to replace yourself on a Superior 2nd Gen Mark VIII.
MonsterMark
Dedicated LVC Member
So easy it is scary.
Pull a plug and check the gap. If you are around .060, change them all.
You really need a cylinder balance test running the engine under load, ie: left foot on brake, right foot on gas, engine at 2000 rpm to see how each coil is firing.
I still suspect the IAC. That is why I said to run some Seafoam. You might be running rich with alot of carbon build up. What do you exhaust pipes look like. (run finger into pipe and see how black fingers get).
I took the car to my friend at Ford today and we ran a cylinder balance test and everything checked out fine. Also did a relative compression test and all cylinders were strong. I cleaned the mass air meter and no change. Also unplugged it to see how it would run and it was much worse. I will run some Sea foam tomorrow and change the plugs and then go from there.
MonsterMark
Dedicated LVC Member
Ya check those plugs. I have found the copper ones last about 25,000 miles before the gap opens too big, usually around the .060 gap.
I still think IAC at this point.
Are you running a chip per chance?
Seafoam first then new plugs. No sense crapping up new ones.
Suck up half the can slowly thru the tube and then try to kill the engine by sticking the tube all the way to the bottom of the can. Anything left over can go in the gas tank. Let it sit 5 minutes or so and have fun.
I still think IAC at this point.
Are you running a chip per chance?
Seafoam first then new plugs. No sense crapping up new ones.
Suck up half the can slowly thru the tube and then try to kill the engine by sticking the tube all the way to the bottom of the can. Anything left over can go in the gas tank. Let it sit 5 minutes or so and have fun.
vr4
Dedicated LVC Member
i doubt its the iac. if youre missing this bad you should have a CEL by now. get the codes pulled and this will tell you what cyl(s) are missing.
get back to me when you get the info.
get back to me when you get the info.
MonsterMark
Dedicated LVC Member
A lot of imported IAC have been bad new so that is why I still question it.
He said he did a balance test so that would show a bad cylinder coil.
I don't think plugs will solve it probably but I'm betting they are worn pretty good.
His buddy could check the IAT also and make sure that is reading correct.
The car has no CEL and no codes. I put the tune back to stock. The plugs I have in there are Autolite 103 platinum which I put in about 20,000 miles ago. I had them gapped to .059 because that's what the GMS 4v connector kit recommended you open the gap to. I wouldn't be surprised if they are at .065-.070 right now. 2 weeks ago I pulled a plug and some oil was seeping by the spark plug towers/gaskets. The IAC valve I replaced mine with about a year ago was a Motorcraft piece.