'96 GT Chugging while driving/idle issues?

[patrickg302]

I have a 1996 GT 5-speed. Bought it a few months ago as a project car, now im trying to work out the kinks. When I start the car it has a funny idle to it. It will start to about 1300 RPM and stay there for a few minutes, i know that they do that sometimes to warm the engine up when its cold outside, but it does it when its hot outside too. When it idles down (which takes about 4 minutes to come down from 1300 RPM) it'll idle up and down between about 700 and 900 RPM its pretty suttle, not violent, but still very noticeable. Now no matter if i'm just driving normaly down the street, or getting on the freeway, as i shift through all gears it chuggs as i accelerate. Even when i'm just at a steady 60 MPH in 5th gear it'll give me some slight chuggs. I took it to get the Check Engine light read and it came up with misfire on cylinder 4 and something about incorrect fuel pressure. I changed all my 02 sensors, and put in all new motorcraft OEM spark plugs, it still is doing the same thing though and I cant figure out why.

The car has 130,000 miles
My only mods are:
K&N cold air intake,
Flowmaster 44's cat back,
and a PI Intake manifold.

any help would be great

 

[wmburns]

Please go to your local autoparts store and have the DTC codes down loaded. There are 1000's of codes and they each have a story to tell. Don't make us guess.

Review the following for information on how to trouble shoot IAC idle problems.

Is your mustang stumbling, dieing at idle or idling rough? - Page 14 - Ford Mustang Forums

Pay special attention the the throttle body idle set screw. Often ppl will adjust it in a vain attempt to resolve an idle issue. If set too high, this could be the source of the symptom.

 

[GDawg]

At what RPMs are you shifting at? Too low and it will struggle.

The car has a warm up period regardless of the outside temp when first started. It may warm up faster on a warm day but it will need the warm up cycle. 700 - 800 rpm is not a bad curb idle as long as it settles and doesn't fluctuate.

Sounds like your fuel filter is way dirty. Or your IAC may be bad or your MAF may be dirty or you have a slight vacuum leak or flux capacitor is the wrong color... ;-)

 

[patrickg302]

Well I usually shift around 2500rpms give or take... So I don't think it's my shifting, it chuggs no matter if I shift at as low as 2000 or as high as 4500rpm. I replaced my fuel filter last weekend so Ive ruled that one out, I also put on all new PVC/breather/air intake type hoses so there all new. And my intake manifold is new, as well as the gasgets are all brand new and sealed up nicely
with rtv...I'm gonna try new wires tommorrow, and stop by auto zone to get the codes read and reply back with the numbers

 

[46stang]

The chugging is likely caused by bad plug wires. I would remove #4 wire, then start the car and see if the spark jumps out of the side of the boot. It most likely will.
The surging idle sounds like a vacuum leak. I would get some parts wash and spray around the intake. The engine will rev up if you find the leak.