Is the mass air flow sensor and overvoltage protection relay hard to replace? And if not, where are they exactly and how do I take them out and install the new components? Car idles and power surges at low speeds or sitting still...dealer wanted $495.00 for a new mass air flow sensor, but Autozone said they had one for $154.99...is this something I can do myself? Thanks for any advice.
~dehaven

 

MAF replacement is a DIY job. No special tools or coding.
However your symptoms don't suggest a MAF fault.
What were the diagnostic codes when the dealer told you you need a new MAF?
P0170/P0173 is the classic signature of MAF.
OVP fitment is DIY. This is a simple relay which is located in the fuse box under the hood. Unfortunately my account won't let me attach a photo. However I have seen other posts with the location shown.
OVP is a device which works or it doesn't. If the voltage goes over 15v (or there abouts) the output from the relay is cut. There have been problems with them (poor circuit board soldering) but if they are at fault you don't get 12v to your Engine Management system and therefore get all sorts of problems.
Idle surge (hunting?) is not a problem I associate with OVP.
Who suggest you need a new OVP and why?
If you wish to resolve your problems get the diagnostic codes read. This is the starting point for all problem analysis unless you want to spend loads of money needlessly changing components.
Stuart.

 

It could be the wiring harness also. I have e320 1995 model. Use to have the same problem. So eventuall had to change the wiring harness. After changing the harness everything came back to its normal. Although it is bit expensive but helps in rectifying the other electrical issues in the long run. The main damaged parts of the wiring harness are around the spark plug and injectors area as they are more exposed to the heat. Secondly the Merc models starting from 1991 to 1995 had a major problem in wiring harness. They had used some cheap harness which creats all these kinds of problems.

Open up few points of the harness and if it is not changed as yet you will find the insulation going off. That can result in short circuting also. So better check the wiring harness first and then proceed with other items.

Hope this will help.