99 idles like a Harley

[Supersport]

Im at the end of my rope. It was running rich, might still be. Lets start with what Ive done....
Replaced...
Cap and rotor
Plugs and wires
New IAC
Cleaned the EGR and installed a screened gasket
Replace all the vacuum lines under the hood.

Cold start in the morning... Idles high then drops to more normal cold idle.
As soon as I put it in gear, rpms go up for a second and then drops back back down were it was.
If I dont wait for the rpms to drop and drop it into gear, it wants to take off until I stop it and let it sit for a second, then it drops down to normalish idle.
After driving, If I put it in neutral or park, it will either almost die or it catches itself and just idles rough.
It runs like a top when its moving but as soon as I almost come to a stop, it gets a rough idle.

Im at a lose as what to do or check next. Any direction would be MOST appreciated!

[HPbyStan]

New gas cap for the fuel tank ??? It's amazing to me how badly a worn out gas cap can make modern stuff run...

[Lumpy]

New gas cap for the fuel tank ??? It's amazing to me how badly a worn out gas cap can make modern stuff run...

I know that a good way to make Fords run better is to unscrew
the gas cap, lift it away from the truck about 16 inches, drive
the truck away and then drive a Chevy into the place where
the Ford used to be. Replace the cap, unless it has a Ford
logo. In that case, go to AutoZone for a new cap.


Lump

[1Gary]

Have you scanned this for any codes??.

You used Delco parts for the cap,rotor,wires and plugs,right??.

Sure does sound like a vac leak.Did you spray the intake with carb cleaner to see if it is leaking???.

Does it have A/C??.The vac control lines for that are prone to vac leaks.

[Supersport]

Have you scanned this for any codes??.

You used Delco parts for the cap,rotor,wires and plugs,right??.

Sure does sound like a vac leak.Did you spray the intake with carb cleaner to see if it is leaking???.

Does it have A/C??.The vac control lines for that are prone to vac leaks.

Well, finally got back in town.

Gary, I had a Check engine light come on, and had a buddy scan it, came up a po420, Catalytic converter.

But before I replace the Cat, i want to make sure I have it running right.

Changed my 02 sensors, they had 140K on em, and it runs and idles alittle better, still not right.

Yep, AC Delco cap and rotor and Platinum plugs. Went Bosch plug wires though. I went around the intake once searching for vac leaks, but didnt get any change in idle. I have plenty of carb cleaner so will go around it again to make sure. Yeah, I have A/C, didnt know that would effect the engine! Learn something new every day! So do I do the same test and spray the hoses down with carb cleaner?

Thanks for the insight.

[mdmead]

Does the 99 have the problem-prone injection spider assembly? Could be a stuck poppet valve giving it too much fuel. (Would run decent as rpms picked up?)

[Smiliesafari]

I think that poppet problem was solved starting with the 1996 model.

[Supersport]

Does the 99 have the problem-prone injection spider assembly? Could be a stuck poppet valve giving it too much fuel. (Would run decent as rpms picked up?)

Well that sounds kinda like it "Would run decent as rpms picked up". It runs like a top, starts one the first crank. Only the rpms go up for a second when I put it in drive , then back down to rough. Only when I come to almost a complete stop does it start idling rough. And if I put it in neutral or park from driving, it doesnt want to stay running all the time now. Went through a half can of carb cleaner looking for a vacuum leak today... nothing. I heard from anther guy that those spider assemblies just wear out, plastic parts again. Wasent wanting to think about that.

[Cobra]

i recently changed my cat and O2's because i had a hole (which i patched) where the previous owner welded in the universal one it improved my low idle stumble however my cat wasn't dead or falling apart but the new cat made a clear difference

[Supersport]

Well I found out I have an aftermarket Cat when I went down to price a new one out... $300 installed. I replaced all the 02 sensors but still havent had any improvement in idle, it runs smoother when its movin. I think my next step is to take it someplace that can plug into the computer and see if it that can tell me anything. I hope I dont have to pull the injectors out. What kind of a job is that? Day, Weekend..... I work outa this thing and cant afford to stop for a day.