map sensor was unplugged.
 

First I know the map has something to do with mixture.My mechanic never hooked it back.Do you think that caused less gas mileage,and throttle having dead spots?It seems to drive much better now,should I disconnect battery so engine will relearn its program?

As far as I am concerned, the MAP sensor actually measures the vacuum within the intake system. If the MAP is disconnected or malfunctioning, the computer will be tricked into something that may be undesirable.
Disconnecting the vacuum line from the map sensor will add unmetered air to the intake (Unless capped off) that probably shows up at the O2 sensor as lean. Computer tries to adjust until it can't anymore. Most likely runs richer (lower MPG)
I believe it is not a good idea to take the MAP out of the loop.
As far as I know, the computer can only do a certain percentage (forgot the exact number) to close the mixture loop. Perhaps your vehicle is in an open loop at this moment and appears to be running better, but it really isn't. Open loop occurs during cold start and up to a certain engine temperature (think 40C) after that the computer needs to close the loop to run the engine efficiently.
I had some problems with my 95 E320 in this area (not the MAP) but it drove a lot better with the problem, but was extremely rich, got about 9 MPG's and didn't pass smog.

I am still learning about modern automobil's and by far not done with it.....

X2, pretty anecdotal but thought the map was basically for open loop then the O2 takes over. Do you have a multimeter? You should measure the duty cycle.


Sent from an abacus

It drives better now,no dead spots in pedal.I will try and go to dealer to clear codes if any.All my power is back and exhaust smells right,and gas guage shows better mileage.Do every one check your plastic hard lines,from time to time.

Perhaps the MAP was the source of un-metered air?
I presume the line was capped off!

No,there was supposed to be a tee,on one of the manifold tits.One going to fuel regulator,the other to map.

I give up. What is a MAP sensor? Are you talking abolut the MAF sensor?
Confused in the desert.

A map sensor picks up vacuum pressure,and sends info to computer to adjust AFR

Is the "MAP" sensor used mainly on diesels then?
Anziani

This was on my 99 s320.I think newer diesels might have one.

The map sensor on this model is for diagnostics and is not part of the main fueling algorithm. Fueling on this model is computed using a mass air flow sensor. At worst I'd expect an air leak and diagnostic related fault codes.