Hesitation??
 

My 98 has been running rough and has a slight hesitation. After letting off the gas the car will coast for about 10 sec and try and stall once. It wont try again till after i give it gas and coast again. I feel no lack of power on accel. Car felt great at atco last week but the hesitation is getting worse. The car throws no codes. I had it on a scanner and the o2, maf, and other sensors seem to be fine. It shows no knock, no misses. Sounds kinda like a vacum leak but sprayed around under the hood with 2+2 and couldnt find anything. Any Ideas? Im gonna check the fuel presure later today but i figured if that was going my car would be runnin lean and knockin. Fuel filter is new and just did an oil change not to long ago. I also changed out my tune.

Seems like you are debugging the way I would. I'd hook it up to a vacuum gauge and check the fuel pressure as well.

what did you change on the tune? i would revert back to what you had and see if the problem is still there.

I changed the tune to one i knew that was good to see if the problem went away but it happend with both tunes something is out of wack

ah ok. how old are the plugs? no exhaust leaks? how are the O2 's?

o2s are reading fine. i have and had a slight exhaust leak for awhile and i need to do plugs but i dont think that is the problem

egr valve?

ahh best tip yet. but wouldnt that set a code?

if it was stuck closed not opening

so its stuck open which wont throw a code

Where's your exhaust leak? If it's before the O2 sensors then they are getting bad information and the computer will be doing the wrong thing. A small vacuum leak will also cause the computer to make adjustments which could lead to an almost stall condition.

i think its after the cats but ive had the exahust leak since ive owned the car and just started having this problem within the last 2 weeks. the car also doest throw any codes

A decent scan tool can show more than codes. Sensors that are almost out of range but not quite enough to trigger the cel. There might be not ready conditions stored as well. You should try to find someone that can plug something in and watch your car run while it's happening. Looking at the O2 readings and fuel trims might help show if it's loading up or leaning out for a brief moment.

i believe he has the ability to watch datastream as he said,

i watched with my tuner and a snap on scanner (brick). Im gonna check the egr tommorrow and also crank sensor, clean my maf, and do plugs

I have a spare EGR if you wanted to borrow it. But you could probably just disconnect the wire harness from the EGR and let it throw the code and then find out if the hesitation goes away. Have you cleaned your throttle body recently? The LS1 pulls a ton of vacuum and that pulls oil vapor through the pcv and really makes the TB dirty. You might want to pull that off and clean it and the passages and iac really good. You can do the coolant bypass while you're at it.

that sounds like a good idea. I ran my car without the filter in down the track and i have no screen since the one that was in there was messed up. So its a good possibility that the tb is dirty