shaky motor at idle need help

[aaron427]

The other day at idle the motor seems to be shaky? I haven't done anything or changed anything on it. You can't feel it when you drive, but if you rev it a little in neutral you can feel it. I plugged the predator up and I have no codes, and my brother looked at the parameters and he said they look pretty normal. He did say the short term fuel trim looked odd. One bank at idle ranged from
-7% to around -2%. the other bank was reading -3% to around 0%. And the long term fuel trim it was dumping like 20% in. I am not familiar with the parameters so that may be normal. Any suggestion where to start? Only mods are 01 ported intake, k&N, offroad x-pipe. I can't think of anything else. This is drving me crazy. Any help would be greatly appreciated. This is on a 99 cobra with around 46,000 miles. thanks.

 

[blown01cobra]

Is the motor stumbling like it wants to shut off or is the whole motor shaking around while at idle.

 

[aaron427]

It idles fine. Doesn't surge or anything like that. If you just jumped in the car and started it you wouldn't notice it right away. My brother drove it last night and didn't notice it but when he sat in it tonight and I pointed it out he noticed it. So it isn't something that shakes the entire car. I hope that explains it a little better. It wasn't doing it last week. So I know it isn't in my head. Thanks.

 

[blown01cobra]

......

 

[blk96SVT]

Idle Air Control valve?

 

[aaron427]

sounds like a bad engine mount.

How can you tell if that is what it is? I am far from a mechanic so you will have to bare with me.

 

[aaron427]

Idle Air Control valve?

That would make the car idle funny wouldn't it? Like rpms jumping around, surging possibly?

 

[aaron427]

could it be the balancer? I looked at it and it seemed to be normal

 

[Taz]

Idle miss? 46K miles? Still got the original plugs in it? If so, throw a new set in there - not platinum.

T-

 

[blown01cobra]

How can you tell if that is what it is? I am far from a mechanic so you will have to bare with me.

Nevermind... I misunderstood what you where talking about.

 

[smkstang1]

Mine also shakes a little bit. You can notice it if you hold the shift knob. I hear it is normal. Not shaking but a small patern like shaking. I believe it is normal and I spent hundreds and hundreds of dollars trying to figure out what it is on my other GT.

Someone can correct me if I am way off.

Nick

 

[aaron427]

Not sure if the plugs are stock or not. I bought the car used. That is on my list to do next week. Just because the engine doesn't throw a mis-fire code doesn't mean anything right? I have always had 5.0's so the 4.6 is a different animal to me. Autolite 764's a good plug to try? I hope it something that simple. Thanks for help so far guys.

 

[aaron427]

Mine also shakes a little bit. You can notice it if you hold the shift knob. I hear it is normal. Not shaking but a small patern like shaking. I believe it is normal and I spent hundreds and hundreds of dollars trying to figure out what it is on my other GT.

Someone can correct me if I am way off.

Nick

I hope that isn't the case because this will drive me crazy. If I turn the radio up loud enough the bass from the 460 will thump enough to cover up the shake. LOL

 

[smkstang1]

every mustang I have been in shaked a little at idle. either it is how mustangs are build or they all have the same problem... it cant be a big problem, because I have never heard any of them complain about it...

hope this helps a little bit

 

[Taz]

Not sure if the plugs are stock or not. I bought the car used. That is on my list to do next week. Just because the engine doesn't throw a mis-fire code doesn't mean anything right? I have always had 5.0's so the 4.6 is a different animal to me. Autolite 764's a good plug to try? I hope it something that simple. Thanks for help so far guys.

Mine had an intermittent miss at idle, but never threw a code. Some OBDII monitors require a minimum number of consecutive occurences before the PCM will throw a code.

Autolite 764's are good copper plugs, and they're inexpensive. Try a set. Maybe they'll take care of the problem. Unfortunately, the 764's didn't cure my idle miss - I had to go to Denso iridiums before the miss was gone. But the Denso's cost like sin - try a set of 764's first.

BTW, I can now idle the car with a drinking glass full of water standing on my KB blower and not spill a drop. That's how smooth it idles.

T-

 

[COBRA CRUIZER]

Stick with OEM parts. Use only Motorcraft spark plugs, make sure you gap them correctly. As far as fuel trims go, What were the readings? SHFT1 & 2 LFT1 & 2

 

[aaron427]

Stick with OEM parts. Use only Motorcraft spark plugs, make sure you gap them correctly. As far as fuel trims go, What were the readings? SHFT1 & 2 LFT1 & 2

I said in the first post what the fuel trim readings were. I will look at it again tonight and post them again just to see. It seemed to idle a little better this morning, but not much. Stock plugs? I have always heard to stay away from the stock plugs. Most guys are running autolites or the NGK's. What kind of plugs are the Denso iridiums? Can you buy them anywhere? thanks again.

 

[Taz]

I said in the first post what the fuel trim readings were. I will look at it again tonight and post them again just to see. It seemed to idle a little better this morning, but not much. Stock plugs? I have always heard to stay away from the stock plugs. Most guys are running autolites or the NGK's. What kind of plugs are the Denso iridiums? Can you buy them anywhere? thanks again.

Probably 99% of the guys on this board will tell you that the OEM platinum plugs blow dead goats. The other 1% either don't have a clue, are on bad drugs, or own stock in Motorcraft.

The only reason Ford installs those lousy Motorcraft platinums is that they're the cheapest plug they can use to show a 10000000000000000-mile plug change interval.

Denso iridium plugs are the sh1t! Most guys will tell you they're not worth the money, and for most guys that's true. But if you've got an intermittent miss that you can't cure with anything else, what's it worth to you to make it go away???

Denso Iridium Power

EDIT: I usually order mine online to save a few bucks, but I've heard that Auto Zone carries them.

T-

 

[aaron427]

Probably 99% of the guys on this board will tell you that the OEM platinum plugs blow dead goats. The other 1% either don't have a clue, are on bad drugs, or own stock in Motorcraft.

The only reason Ford installs those lousy Motorcraft platinums is that they're the cheapest plug they can use to show a 10000000000000000-mile plug change interval.

Denso iridium plugs are the sh1t! Most guys will tell you they're not worth the money, and for most guys that's true. But if you've got an intermittent miss that you can't cure with anything else, what's it worth to you to make it go away???

Denso Iridium Power

EDIT: I usually order mine online to save a few bucks, but I've heard that Auto Zone carries them.

T-

for example me. I have no clue if they are good or bad just going off of others experience. Those plugs are close to $100? Ouch. I will have to get some more research done on that. Thanks for the info so far. What are better than the autolites, but a little less than the Denso?

 

[Taz]

for example me. I have no clue if they are good or bad just going off of others experience. Those plugs are close to $100? Ouch. I will have to get some more research done on that. Thanks for the info so far. What are better than the autolites, but a little less than the Denso?

Some prefer the NGK TR55's or TR6's (colder plug). NGK also makes iridium plugs that are less expensive than the Denso's, but I don't know how well those have been working out for folks.

T-