nickbartels

I am working on my sisters 99 GT 4.6L. She took it in to a shop and had new plugs boots and a fuel filter installed. Well thats what the shop said was wrong. It will idle well with the car in park, but when put in Drive, the idle will surge and the car will lunge forward. It has died in traffic a couple times.

I have cleaned the IAC but had no improvement.
I have replaced the IAC but had no improvement.
I have cleaned the MAF but had no improvement.

I drove it about 15 miles and now it is even worse than it was. Now when I take off or even just rev the engine while in park, it hesitates and then acts like it is not firing on one of the cylinders. I have disconnected a cylinder at a time, but with each coil pack, it bogs more, so I don't know what the heck the problem is.

Any ideas?????

Thanks
Nick

Fat Nick

Get at the throttle body and look for the idle set screw. While the car is on you turn the screw and it will set the idle up a little. My car had exactly the same problem, this fixed it and costs nothing.

nickbartels

Fat Nick,

Thanks for the fast reply.
The shop had set it higher a couple days ago and it was still not running right. I have since set it back to factory spec. The TPS shows the perfect .99 volts Key on, engine off. I am just dumb founded with this problem and really want to figure out what part is causing this.

Fat Nick

When you said it had new plugs boots, what do you mean? Does it have new spark plugs? New coil packs? Or both? The reason I ask is 8 new plugs/cp's and install is close to $1,500. More than likely just new plugs were put in. Pull the plugs and check the gap. Might be gapped to much or too little. I'm running .035 on mine now, but mine has a few things on it as well as a tune, stock is supposed to be around .053, get in there and set it about a .050 and you should be good to go there.

Mine did this same thing right after I put my new plugs in, before it was fine. Make sure all the coil packs are connected, and disconnect the battery for about 30 minutes to reset everything. Also you might want to go ahead and set the idle back up. I found the best/smooth idle in park is around 800rpms.

Also other causes could be since it is 6 years old, is that it could need a new fuel pump or a new coil pack. An idea you can use by learning from my mistake is, if the CEL for the coil pack comes on, buy it yourself and install it, you will save $70 and it takes about a minute to install.

Hope this helps you out.

nickbartels

What I meant by boots was the connector from the coil pack above the spark plug that leads to the plug itself (basicly the plug wire). I have raised the idle enough so I could get the car to my house from my sisters house, but it still is not firing on all cylinders. I think a coil pack is being flacky so I will probably get one on Tuesday and see what I can get accomplished. I am hoping it is just a coil.

Thanks again
Nick

PipsBlackStang

Im assuming no codes are being spit out??? Go to advanced auto and ask them to scan if for you. That may clear up some things..but then again maybe not.

jdaniel

Is there by any chance a timing adjuster on he car? Did she wash the engine while the engine wasnt running? Ive had this happen to me twice and I found out both times what it was.

1) If you have a timing adjuster on a PI 4.6 and you advance it to anything above 15 degrees then the engine will surge like crazy. I cant remember the exact reason.

2) I washed the engine at a car wash one day and water got into the MAF and screwed it up. Just take it off and hit it with a blow dryer for about 20 minutes and the water will evaporate and it will run like normal. Also check the plugs... I had some water somehow slip through my threads on my sparkplugs allowing water down in the cylinder. I took them out and seen wated there so I took a wet/dry vac and sucked it all out and cleaned my engine also.

jdaniel

Ummm... this isnt how you set the base idle on a 4.6. What you do is unplug the idle air bypass ( the plug that goes in top of the IAC). The car will do one of two things when this is unplugged. It will either try and die and idle somewhat roughly or it will idle up a little just a little. Either way you need to adjust the idle up or down to 600 rpms while its unplugged and plug the IA bypass back in and it should take the cars base idle up to about 850 to 900. If you adjust just the screw and forget about the IA bypass then you will have a high hang as you slow down or when you just rev the engine.

nickbartels

Ok guys,

I have now replaced a coil pack for cylinder 6 and now it runs like a champ...Except for the crappy idle issue.

jdaniel, I have now done what you recommended for setting the idle and it still has the same problem.

Any more suggestions would be great!!

Thanks
Nick