Help me get my car to run proper - Bucking at low rpm, idle prob, power loss?

91LX_5L

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May 13, 2002
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British Columbia
I know I posted this on a few other forums im just trying to get as much help as possible...

I have H/C/I 5spd. World Windor Jr heads, E303 Cam, SVO/Cobra Intake.

Before you go there
Maf = Clean
IAC = New
O2s = New
Plugs/Wires = good
Fuel filter = good
PCV = Tight as a nun
Timing = 14*, 91 Octane

1.) If I let my car idle down to around 1200rpm it will start bucking like crazy.
2.) If I first fire up my car the rpms go up and hang for a bit then drop down and car stalls, more often when WARM.
3.) Car seems to be lacking in lower RPM power or power all around. stock 91 5.0 can keep up easily
4.) Sometimes when cold car hesitates and sputters when accelerating lightly at low rpms (taking off in 1st gear)
5.) I will get the odd burp/backfire when accelerating (rarely)

Please help me solve this problem.

Now my egr valve is capped off (off intake area?) & Im running fox headers. I plan on doing a smog delete anyways and dont have emissions here.

Im thinking a vacuum leak? You know those feeble red/green/white/pink? plastic vaccume lines? If they are leaking (any of them?) could this be my problem? Where do they commonly leak?

Thanks so much in advance!
 
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Havent changed anything, its been like this for quite a long time but seems to be a bit worse now and I just want to deal with it.

ECT sensor, is there a way to test it? clean it?

UPDATE. I looked for vacuume leaks quickly with propane didnt find anything.
But you know the rubber plug on the passenger side where the red, green, white, pink? vacuume lines plug into? Heres a pic, not my car.
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I unplugged it and passed propane directly at both ends and nothing happend to my idle??? AND If i unplug it and blow into the female end I hear air escaping which sounds like its down in my inner passenger fender...is this normal?
ALSO...my egr is capped off and the vaccume line is still running to it could that be effecting anything?
 

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I'm running a pretty modded motor on a stock ecu and lots of those problems sound normal to me. Although, i was having an issue with the car stalling out when hot also. My mechanic narrowed it down to the IAT. When it got above 110 deg. or so the car would act more funny than usual and stall out. We moved the IAT sensor to the fender by the air filter and the cars been fine since. Idon't know why it works but you may wanna give it a try.
 
The IAT is the sensor in the inlet tubing (somewhere. I'm not sure where it is on a stock inlet. Might be in the box). It shares the e-harness with the MAF sensor if you trace it that way.

That vacuum manifold is for the EGR actuation and TAB and TAD IIRC. If you have no EGR function or Smog function, I guess those are no biggie.

Do ensure the source lines feeding the slaves (inside the passenger fender. Remove the wheel liner to look at them) are not still hooked to manifold vac or you could have a leak when the solenoids open).

I'm no Grady or Wes (et al) but my first thought was also about the state of tune. IIRC, you had an RT before your trip? Did that smooth things out?

Good luck.
 
ahh is the IAT also known as ACT? I have a BBK CAI and its after MAF? The little black sensor with a red wire in the middle? Its supposed to be facing so air blows THRU it right?

I dont understand what your talking about with the source lines? Why shouldnt they be hooked up?

I never did ending up running my tweecer actually...
 
hey Matt, glad to see you tinkering w/ the stang!

for #2: might wanna check your TPS voltage w/ a volt meter. it should be at .99volts or less at idle. if it's more than a volt, it'll tell the IAC to open up, hence the raised idle. i just fixed this on my car today.

moreover, you wanna make sure that the stop screw on the throttle quadrant is not screwed too far in. from what i understand, it's only purpose is to keep the throttle plate from touching the inside of the throttle body and prevent it from sticking.


as for the rest--if you're not gonna datalog w/ the RT and use EA to calculate things like injector timing table values, i'd seriously consider calling Don @ Lasota Racing for a mail-order tune. the tune will help out w/ driveability a LOT!

what are your coolant temps like? from what i read, the hotter they are, they more timing the ecu pulls.

try spraying brake cleaner to check for vacuum leaks around the intake, throttle body, etc.

good luck, man.
 
ahh is the IAT also known as ACT? I have a BBK CAI and its after MAF? The little black sensor with a red wire in the middle? Its supposed to be facing so air blows THRU it right?

I dont understand what your talking about with the source lines? Why shouldnt they be hooked up?

Yep, the two sensors/names are the same.

There are vacuum lines (with manifold vacuum) going to the emissions solenoids in the fender. If the lines leaving the solenoids and going to the various components are not connected, you end up with an air leak when the solenoids open (instead of actuating a device, the line is just sucking air).

If you disconnect the 'feed' lines (supplying manifold vac) to the solenoids, or disable the solenoids, this should keep the leak from occurring.
 
Paul thanks man, yeah last time I checked my TPS it was good. Thanks for the tips.

maifold vaccume gauge I dont see why mine wouldnt be hooked up? sorry man im tired mabye im just being a dumbass and not understanding you?