shaky motor at idle need help

[quick01snake]

i like the 764's just fine...
mine has a slight shake at idle also....started doing it after i got my car tuned and the guy turned my idle up from like 650 to 800-850....not very noticeable until you TRY to notice it...i also think my motor mounts are starting to go, having 127K miles on them and all....

 

[aaron427]

i like the 764's just fine...
mine has a slight shake at idle also....started doing it after i got my car tuned and the guy turned my idle up from like 650 to 800-850....not very noticeable until you TRY to notice it...i also think my motor mounts are starting to go, having 127K miles on them and all....

good point. When I hook the predator up tonight I will see what it idles at. I believe it was around 850 or so. How can you drop the idle? You have 127k on your car? How is everything holding up? Original motor? That is encouraging to hear.

 

[aaron427]

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-

I will check into them. what is the gap for our cars? Thanks again.

 

[lemosley01]

i like the 764's just fine...
mine has a slight shake at idle also....started doing it after i got my car tuned and the guy turned my idle up from like 650 to 800-850....not very noticeable until you TRY to notice it...

+1

No codes or anything thrown, and the car has always done it in the 1+ year I have had it. I changed the plugs and that made no difference.

My idle is right around 750-800RPM.

It is just the way mustangs are. I think it's cool, but it would be cooler if it were the big shake induced by a lopey cam.

 

[aaron427]

+1

No codes or anything thrown, and the car has always done it in the 1+ year I have had it. I changed the plugs and that made no difference.

My idle is right around 750-800RPM.

It is just the way mustangs are. I think it's cool, but it would be cooler if it were the big shake induced by a lopey cam.

Mine just started doing it. I have had the car about 3-4 months. That is the only reason it bothers me. I agree some big lopey cams would be nice. :rockon:

 

[quick01snake]

i don't have the original engine, it was replaced under warranty at 43K miles...so i guess this engine has 84K or so on it, strong as ever....only things i've had to replace are the normal wear items, brakes, tires, both outer tie rod ends, IAC, clutch (didn't go out, i just upgraded), and i'm kind of hard on trannies....on my fifth one now, of course the first three were tr3650 POS's that COMBINED only lasted 33K miles of the 127K total....the last two have been t45's...first lasted like 40K miles until and unfortunate shifting misfortune, second is still in the car, almost 50K miles later, sychros are now starting to go bad though...

 

[Quadcammer]

I will check into them. what is the gap for our cars? Thanks again.

gap is .052 to .056.

.054 is the winner. :beer:

 

[aaron427]

i don't have the original engine, it was replaced under warranty at 43K miles...so i guess this engine has 84K or so on it, strong as ever....only things i've had to replace are the normal wear items, brakes, tires, both outer tie rod ends, IAC, clutch (didn't go out, i just upgraded), and i'm kind of hard on trannies....on my fifth one now, of course the first three were tr3650 POS's that COMBINED only lasted 33K miles of the 127K total....the last two have been t45's...first lasted like 40K miles until and unfortunate shifting misfortune, second is still in the car, almost 50K miles later, sychros are now starting to go bad though...

That's not too bad then. The trans sucks. My first power shift in this car was a rude awakening for me. When all it did was scrap and grind going into second. From that moment on I have yet to even speed shift the junky thing until I can swap trans. My old 95 cobra had 220,000 miles, and the trans had never been touched and I use to beat the crap out of that trans. I even learned to powershift using that car. So it took alot of abuse. Is the IAC a common problem on these cars? I have read multiple posts about them being changed. thanks.

 

[aaron427]

gap is .052 to .056.

.054 is the winner. :beer:

just found that info right before you posted it. thanks.

 

[quick01snake]

Is the IAC a common problem on these cars? I have read multiple posts about them being changed. thanks.

mine started acting up intermittantly around 110K miles....finally gave out completely a couple thousand miles later...it was like 85 bucks and 2 minutes to change out....

 

[green99_svt]

if you have a long term ft of 20% on one side and not the other there is a problem. most likely a missfire. could be a dirty injector. vac leak on one cylinder/bank. or a bad coil pack. the engine is adding 20% more fuel on that side than the base table.

 

[aaron427]

if you have a long term ft of 20% on one side and not the other there is a problem. most likely a missfire. could be a dirty injector. vac leak on one cylinder/bank. or a bad coil pack. the engine is adding 20% more fuel on that side than the base table.

it is adding that much on both sides. I haven't been able to mess with the tuner yet because I have to get the stock program put back in the car before I can use the predator, but I can datalog with it just can't change anything with it yet.

 

[aaron427]

mine started acting up intermittantly around 110K miles....finally gave out completely a couple thousand miles later...it was like 85 bucks and 2 minutes to change out....

What did it do when it acted up? Will it just not idle properly?

 

[quick01snake]

What did it do when it acted up? Will it just not idle properly?

mine wouldn't idle at all...to keep it running you had to press the gas pedal a little...

 

[green99_svt]

it is adding that much on both sides. I haven't been able to mess with the tuner yet because I have to get the stock program put back in the car before I can use the predator, but I can datalog with it just can't change anything with it yet.

then you have a vacuum leak some where. 20% is to high. the tuner cannot do anything for part throttle fuel tables. find the vacuum leak you will solve your issue

 

[aaron427]

then you have a vacuum leak some where. 20% is to high. the tuner cannot do anything for part throttle fuel tables. find the vacuum leak you will solve your issue

The car has been dyno-tuned and the computer was reflashed. Could that have anything to do with the readings being funny? Do you know what the readings should be? Any other parameters that I can check? I did think of a couple of things it could be. I think I have an exhaust leak that is getting worse. Plus when I bought the car it had breathers in both valve covers. Well the drivers side kept spitting oil on the firewall so I put the stock PCV back on it. I just got my tube so I can get rid of the other breather this weekend would that cause a vacuum leak? Just running the one breather? Thanks you are giving me some things to look at.

 

[Taz]

You don't necessarily have a leak. You DO have a ported intake. That will lean you out and cause your fuel trims to rise. Another mod that will do the same thing to a lesser extent is a C&L MAF meter. Put the two of them together and you'll go lean enough to start throwing codes.

Believe me. I've been there. The only solution for me back when I was N/A - short of removing one of them to bring the LTFT's down below 25% - was to install a MAFterburner fuel trim tuning tool.

T-

 

[aaron427]

You don't necessarily have a leak. You DO have a ported intake. That will lean you out and cause your fuel trims to rise. Another mod that will do the same thing to a lesser extent is a C&L MAF meter. Put the two of them together and you'll go lean enough to start throwing codes.

Believe me. I've been there. The only solution for me back when I was N/A - short of removing one of them to bring the LTFT's down below 25% - was to install a MAFterburner fuel trim tuning tool.

T-

I went back to the ad of the listed mods that the car had, and low and behold what do I see? It says a ported stock mass-air. Could that be the culprit? Is it bad for it to be running around 25% is that lean or rich? What exactly is a mafterburner? thanks.

 

[Taz]

I went back to the ad of the listed mods that the car had, and low and behold what do I see? It says a ported stock mass-air. Could that be the culprit? Is it bad for it to be running around 25% is that lean or rich? What exactly is a mafterburner? thanks.

Okay, it goes like this: your MAF meter under-reports your air flow, so your PCM WAS providing only enough fuel for the reported amount of air. BUT it's a feedback system, and after finding out (via the O2 sensors) that the mixture was a bit lean by 20%, the PCM richened up the fuel trims to compensate, hence the 20% LTFT's that you are seeing. As long as the PCM can bring everything back into line with less than 25% compensation, everybody is happy, and you're not going to get any trouble codes. It isn't until the PCM can no longer compensate within its +/- 25% range that it begins to complain.

That takes care of what's called the closed loop fuel trims. You're okay there. Now, NORMALLY, without a dyno tune to compensate for the skewed MAF readings, you'd actually be RICH whenever you go WOT. The reason for this is that the PCM uses a value called the OLFM (Open Loop Fuel Modifier) to adjust the table lookup fuel values it uses for open loop (WOT) operation, and it derives the OLFM from the amount of compensation it has to provide via the LTFT's. But your tune should have taken care of this.

Confused yet? Okay, let me simplify. You're okay in closed loop mode, because the PCM was able to compensate for the MAF meter's under-reporting of the air flow. AND you're okay in open loop mode, because your car has been dyno tuned, and adjusting the A/F ratio is part of that process.

T-

 

[aaron427]

Okay, it goes like this: your MAF meter under-reports your air flow, so your PCM WAS providing only enough fuel for the reported amount of air. BUT it's a feedback system, and after finding out (via the O2 sensors) that the mixture was a bit lean by 20%, the PCM richened up the fuel trims to compensate, hence the 20% LTFT's that you are seeing. As long as the PCM can bring everything back into line with less than 25% compensation, everybody is happy, and you're not going to get any trouble codes. It isn't until the PCM can no longer compensate within its +/- 25% range that it begins to complain.

That takes care of what's called the closed loop fuel trims. You're okay there. Now, NORMALLY, without a dyno tune to compensate for the skewed MAF readings, you'd actually be RICH whenever you go WOT. The reason for this is that the PCM uses a value called the OLFM (Open Loop Fuel Modifier) to adjust the table lookup fuel values it uses for open loop (WOT) operation, and it derives the OLFM from the amount of compensation it has to provide via the LTFT's. But your tune should have taken care of this.

Confused yet? Okay, let me simplify. You're okay in closed loop mode, because the PCM was able to compensate for the MAF meter's under-reporting of the air flow. AND you're okay in open loop mode, because your car has been dyno tuned, and adjusting the A/F ratio is part of that process.

T-

Confused yes. I am just now trying to get into the tunning and how it all works. But you explained it very well. So I shouldn't have anything to worry about then? I have not done any datalogging at WOT yet because I just got the car back from the bodyshop. I hope to do some this weekend. When i do so what should be my main focus point to really watch? How does the short and longterm fuel trims work at idle? The PCM will still add fuel just like if I was giving it gas? Of course it wouldn't dump as much fuel. You have been very helpful so far. thanks.