My 99 4l is driving me crazy. Replaced iac and mad. When mad is plugged in, car sputters won't respond to throttle and won't stay running. Run a w/o mad connected, but not great. Codes were for mad, o2s, and iac. All sensors were new, not remain. Egr sensor is not connected from a previous problem that is not fixed. Haven't replaced because it was running fine without it. Code for r the egr too.
any ideas why maf makes things worse? Car was running great without egr and o2s for a long time. Didnt replace maf wires.

 

Sounds like you have a bad vacuum leak somewhere,or maybe a wiring problem. You probably wont be able to solve the problem without a vacuum gauge and a scantool. I use a Creader 3001.

 

Codes rarely mean a sensor is bad, it usually means sensor is working and a problem was detected by that sensor, so "don't shoot the messenger"

What were the exact codes, full list here: https://therangerstation.com/tech_li...II_codes.shtml

You will see that each sensor will have several codes, computer picks a code for a reason, the codes it does NOT pick can help you as much as the code it did pick.
Codes were meant to be used with Full List, a Google search of just one code number will usually send you down the wrong path.

Exact codes are needed

I assume "mad" = MAF?

In Reno you really need a working MAF sensor because of the elevation above sea level, thats one of the reasons a MAF sensor is used, elevation
Air/fuel mix is a WEIGHT RATIO, gasoline uses 14.7/1 weight ratio
That's 14.7 POUNDS of air to 1 POUND of gasoline
or
14.7grams of air to 1 gram of gasoline

At higher elevations the air is thinner, so weighs less, the MAF determines how much less it weighs
Cold air is heavier than warm air, i.e. "hot air rises" because it floats above the colder air, so it lighter, MAF and IAT(intake air temp) sensors detect that
Correct WEIGHT of the air is very very important in getting an engine to run well

This is why vacuum leaks effect an engine, unreported air is coming in, so MAF sensor data is incorrect, this throws off the computer's calculation.
And ANY air leak between MAF sensor and engine will do the same, if the long air tube between MAF and engine is not sealed well or is cracked, then unreported air is sucked in throwing off the calculations

A non-working EGR system would just cause pinging/knocking when accelerating as a symptom, as long as the EGR valve itself is not leaking exhaust into the intake or the EGR tube at the exhaust manifold is not leaking.