Rough Idle Two Mecahnics can't figure it out!!

89 s10 4.3L 4x4

For about 5 months now my s10 has been idling very rough. It surges and idles high for a few seconds, then drops down and almost stalls and sometimes does stall. It is to the point where I have to keep one foot on the gas and one on the brake at stop lights to keep from stalling. Once any little gas is applied she runs fine, however I burn alot of gas.

Things that have been replaced 6 months prior to current problem due to unrelated problems.
TPS
O2 sensor
Coolant Temp Sensor
Plugs,wires,cap,pcv,air/fuel filters, coil
alternator
all vacuum hoses
egr

The truck was running fine then it developed a severe bog problem, ended up being the cat converter, replaced that and she ran better than ever for about 2 weeks. Then all of a suddend she started acting really funny, idleing really rough and misfiring underload. Turns out the #5 plug boot was torn causing the wire to arch. Replaced the wire and fixed the misfiring but not the rough idle.

I took it to a shop and they looked at it, ran codes ect. (which said she was running rich) they thought it was my fuel press regulator. There was a gas smell and the injectors seemed to be spraying too much gas. Found a refurb tbi on ebay fairly cheaply and replaced both injectors and regulator. No fix and they were out of ideas, had tested voltages on all sensors.

Second shop, performed similar diagnostics and could not find the problem, their next thought is the computer. Shop owner (great guy) has another 89 s10 with the same comp that we are going to try swaping later in the week before I buy one. But that is all he can think of left to try.

Some history not sure if it is related to problem or not.

Runs better with egr disconected from solenoid
I had leaky radiator by the ECC canister and alot of colant leaked on it.
arching plug wire
new catalyic converter after o2 sensor put on
My new TBI unit came with a IAC niether the new or old made a difference. however if i take out the IAC and manualy depress it and then reinstall. She runs better for a bit, untill the IAC resets i asume.
It seems to definatly be a mixture problem, more air makes it run better.

I am stumped any ideas would be great. Thanks

A good quick check.
Get a vacuum gauge and give us the engine vacuum readings at idle and at 2K rpm.
Also not the vacuum gauge needle for flckering.


Look around for a third mechainic and find one that knows what he is doing.

Tips on finding a good repair shop.
Check around Ask around
Word of mouth.
Family friends coworkers neighbors business people and delivery people.
Mailmen and parcel delivery people get around and notice a lot of stuff.
Even a good parts house knows what shops are good and not good.
Chamber of commerce and better business bureau and city hall.
If you find a good referral to a repair shop go look them over and talk to them.
Look for a clean looking busy place with nice people running it.
Ask a few questions and ask about their qualifications and training.
Not all places have trained tech/mechanics.
If they do not find a place that does.
Even all dealers do not have all trained techs/mechanics.
MT