rough idle with slight hesitation

Having an issue with my 96 RMW. Has an idle issue that varys from time to time. I could start it 5 different times and it could be different everytime. Very noticable in gear just sitting with foot on brake but when I take my foot off the brake in gear and let roll without using gas, its kind of jerky till the throttle is applied. I believe the car sat for a while before purchasing. No driveability issues under partial or full throttle. I have repalced the plugs and wires, cleaned the MAF, and sprayed the inside of throttle body with a cleaner. This issue doesn't keep me from driving the car, put about 300 miles on it last weekend and avg almost 23 mpg.

I would start with a new fuel filter and begin looking for vacuum leaks.

Pull the IAC off the throttle body and clean it,..clean the throttle body bores too.

sounds like the IAC is not reacting quick enough,. as tim said tho,. assuming you have no vacuum leaks,.
low fuel pressure is more noticeable under full throttle ,..

The issue is really evident when going forward or in reverse with wheels at full lock from a dead stop. I will go ahead and change the fuel filter and clean the IAC and bore.

As i mentioned i would hold off on the fuel filter,. it takes very little fuel to move around at just above a dead idle,. and you mention that cruising and WOT were not a problem,.

but go ahead and do what you want,. you're gonna anyway.

A small EGR leakage can affect idle.

buickwagon wrote:

A small EGR leakage can affect idle.

the 8051 pcm has enough in it to compensate for small egr leaks,. you will notice a hesitation off idle till it re-calibrates,.

I found a couple semi cracked vacuum lines, didn't change. I am going to go with its more of a vibration. If I give it very little throttle in park it will go away and then it will come back as the rpms increase. Can feel it through the whole car. Feels like something is out of balance. How reliable are the harmonic balancers?

My suggestion: You are feeling cylinder to cylinder torque variation due to combustion dynamics issues. Assuming the ignition system is okay, I would suspect the fuel injectors since the idle conditions you list require the absolute lowest duty cycle wherein any injector dynamic flow problems and nonlinearity will manifest themselves.

I would have the fuel injectors cleaned or replaced with new, and see if the problem goes away. I used witchhunter performance and they found one bad and two questionable injectors on my old '94. The car ran much smoother after that.

I'm with Sherlock: this sounds more like cylinder imbalance than mechanical imbalance. The 96 id OBDII, so you could check for misfire data with a scan tool. Also, check the optispark vent system for proper operation: if the air supply is unduly restricted, the vacuum can cause some strange spark issues inside the cap. And idle produces high vacuum.

My brother in law had a good used opti so we switched it out with a new cap and rotor. All is good but the funny thing was the harmonic balancer hole where it slides over the crank was not perfectly round and had been replaced once before. Needless to say a new was put on. Now I am a little suspicious of why its on its 3rd? balancer. We mic'd the shaft it was ok and so is the pulley for the fan that bolts to the balancer. Any thoughts?