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Discussion Starter #1
hey guys so I sold my 95 tbird to buy a 97 tbird with 4.6 motor. car drives great and looks pretty good. only thing is when im stopped in gear with my foot on the brake the motor idles rough. In park i dont have this problem.
Also when im driving along and my rpms are in the 2 grand area and I come to a stop sign this occurs: I let my foot off the gas to begin braking but its almost like the car wants to keep going. The rpms dont drop as the should.
Yesterday I changed my plugs and wires with new motorcrafts. she is a little more peppy but those same 2 issues didnt go away.
I did some searching and only thing I came up with is maybe a bad IAC valve? my car isnt throwing a code either.
 

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Both of those things could be a bad vacuum hose somewhere.

Check all the hoses, especially the hard to get to EGR ones.

Also, gently pull the spark plug boots, and see if there's fluid in the wells.

Vacuum leak+coolant is probably a bad intake manifold gasket.

I've had all these problems. :)

In my experience, a bad IAC won't idle at all, but you can keep it running with your foot on the gas.
 

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Sounds like your power brake booster. I had a neighbor that had that had a massive leak on his Bronco II brake booster, it would start up run for a couple seconds then die. He ended up selling it to a guy I worked with and the buyer figured the problem. It's just one of those things that get over looked.

Read ya later, Nick
 

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was having some rough idle almost stalling at times from cold start to hot did not matter.

was ready to replace the idle control valve.

turned out to be a bad Air temp sensor.. no check engine codes at all.

I Unplugged it and engine ran nicely.

replaced and running good again.
 

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Discussion Starter #6
ill check out these cpl areas this weekend and see what i get. Ill keep you guys updated thanks for the help
 

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Discussion Starter #7
So Ive changed out the IAC valve, cleaned my MAF, changed out all the bad vac lines. She still has a the occasional vibration when stopped in gear. Definitely noticeable performance difference with changing bad vac lines. She sounds beautiful when Im on the gas or in park. I tell ya this vibration thing is aggravating the hell out of me. I never did check the brake booster so ill probably do that next. If anyone has any helpful advice I appreciate it.
 

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If it's the original IAC, you might try a new one.

I'd grab one cheap from a JY; and if it changes the problem, it's worth buying a new motorcraft one.

Don't buy a cheap one, you'll be disappointed.
 

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Discussion Starter #10
ya I already made that move but exactly. I just went to advanced auto and bought a BWD brand IAC valve. I didnt notice any change in performance untill I changed those hidden vac lines going to the canister behing pass headlight
 

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There are 8 pieces of hose in that line; did you get them all?

:grin2:

There's a thread here somewhere; but TB, frame rail, evap cannister is 3 pieces, under pass fenderwell plastic, next to fuel filter, near gas tank.
 

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You never said what the idle RPM is, but assuming it's low? Cleaning the throttle body will bring up a low idle a pinch. When it gets dirty it's restricted so there isn't as much air going around the throttle blade.

Al
 

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Discussion Starter #13
hmm maybe thats the rest of my issue. I didnt change any vac lines near gas tank or near fuel filter but did change the rest. As for idle RPMs, shell normally idle around 800 after warm up but when its idling sloppy more like 550-600ish
 

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If you pull the inlet tube off, hold the throttle blade open and look at it.

If it's black, it needs to have the blade and throat area cleaned.

Spray it with carb cleaner, then use a rag to remove all the black crap in the throat area, and get the backside of the blade; Especially the edges.

Be careful not to bend it, lol.

The black crap where it closes will cause off idle problems, in that transition region; I guess if it's bad enough, it could make it not idle.

Don't indiscriminately spray a bunch of carb cleaner down in there; you'll wash the black crap in the intake into the cylinders as a glob, and that's not good. :)

This being a 97, you could do a PI intake swap, and thoroughly clean the throttle body; eventually the EGR passages muck up. :D

It's a lot of hassle to clean out the intake/TB, so having a reason to unbolt it makes it easier.
 

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Discussion Starter #15
The previous owner did update the intake to the aluminum crossover style. Im not sure if its a pi though. I can't see into the valley enough to tell whether its pi or not. there must be another way to determine this and I just don't know of. somebody else mentioned to me the TB elbow can build up junk that will cause this idle issue.
 

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There's a way to tell if the intake is a PI; the runner in front is opposite sides, IIRC.

The thing you don't want is a Dorman intake, lol.

Cleaning the TB blade up will probably help a bunch; I do that every few oil changes, so I think of it as maintenance.


This is a PI intake:


The stock one is different looking in front, iirc.

You also need a different coolant tube, and other parts; and you will want to order the second temperature sender drilled and tapped, unless you have a set of NPT taps.



The Butt dyno loves this mod, and it doesn't really require a tune.
 

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Discussion Starter #17
Thanks for that information bud. Im gonna pop the hood and look at my intake so i can determine what I have.I got the rest of the vacuum lines I missed except the one near gas tank. I got a pick under it and gave a tug but didnt budge. I didnt want to break the hard plastic line that runs up side of gas tank. Also correct me if Im wrong but thats just a ventilation line and doesnt actually vacuum pulling threw it. The vac line appeared to be in decent shape also so i left it alone.
 

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I left the one near the tank alone also, too hard to get to. There is a vacuum pulling on all of those lines, to varying degrees based on the operation of the solenoids.

Al
 

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Discussion Starter #19
Unfortunately I do have the non PI intake. At least its been updated with aluminum crossover. After driving car a few days after changing all vac lines but that one near gas tank I noticed shes a little smoother on the acceleration. Vibration at an idle is still there but not as bad.
Im wondering if maybe the vapor canister or vapor purge solenoid are bad. Vibration goes right away once you give her gas so must be a vac leak somewhere. Does anyone know if theres a way to test those 2 components?
 
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