occasional miss and backfire
 

My 93 300e 2.8 occasionally will miss and backfire. When it occurs, granted rarely, it is usually when I stop for a sign or light and then take off right away. The car will stumble, miss, then backfire before taking off. It also happens occasionally when put into reverse upon hot starting. Other info that might be related: The weather is hot right now, codes are present for egr bad and for upshift sensor (both ongoing problems i havent got around to fixing as I have no smogging problems and my cold running seems fine without the car holding a gear forever). The other intermittent problem I get is a surging Idle, most prevalent in reverse. This one has me stymied. Thanks for any advice.
Brooke.

My guess is that you have a bad engine wiring harness.

It could also be a bad coil wire or bad resistor boots.

It could also be a bad throttle actuator or a bad mass air meter.

It could be a combination of any of the above.

There is an unbelieveable amount of info in the archives on all of the above.

I would start out with a search for "engine wiring harness".

wiring harness
 

Ah, I should have mentioned that I had the wiring harness replaced about two years ago. The plugs were replaced last in November, though it has been a while for the plug and coil wires.

You may well have a sicking EGR valve that is not completely closing after decelleration..
An easy test for intermittant EGR is to pull the actuator vac line off the valve and plug it..then give the egr a couple of light taps to help it seat.
Drive the car and watch for re-occurence...if none, change the egr to the new up-grade [ TSB campaigne] part.
Don't clear the CE egr code til after test...as the test will pop it anyway..
Look for vac leaks at the same time....

I will try the EGR. I did not suspect it, as I have been living with the code for inop EGR for a couple of years :) and the problem is much newer. I did try disconnecting the EGR and putting a golf tee in the vac line but no diff in running. I guess I will try the new EGR, a coil wire, and check out the throttle actuator, though I heard that is very $$$. Thanks!!
Brooke

If no difference with golf tee, that eliminates egr as suspect for that particular problem.
I only mentioned that cuz you had the egr code and assumed they were at the same time..[egr is likely plugged tube at intake/head side ] but that would not point to your problem.
As money is always an issue with diagnosis, I recommend trying the low $$/ easy test possibles first..
.. next on the list would be to change the resistor boot plug connectors under each coil .
Common ignition fault and good insurance $$$ spent at the same time.
You may also want to archieves a led/sw tool that will let you get to the ignition pin # 8 for more specific codes... that will give you some direction on both fuel and ignition management faullts..
You may also want to golf tee the purge valve line to the intake , as this is a no $$$ test and will verify that the valve is not sticking open and causing an internal vac leak...again, tee it and try the test run...

In addition to the sticking EGR valve, your hot intlet tube from the EGR valve to intake manifold could be plugged up and need to be reamed out.

Steve Brotherton (stevebfl) has an article posted in the DIY link at the top of the page that illustrates this problem. I think the article is called Evalutating Electronic Engine Controls.

Also, While you may have a bad coil wire, it is more common that the problem is a bad connection between the coil wire and its resistor boot. Change the three boots under the coil wires first.

resolution
 

Just wanted to follow up (cuz I hate when people dont!)
I finally got around to running a speedo cable through the egr tube. It is hard to know when you reach the intake side so I looked down the held-open throttle actuator with a flashlight until I could see the tip of the cable poke through.
In addition I changed the coil connectors and put in new bosh super plugs.
Problem solved!!
Don't know which it was but regardless it is fixed and no more check engine light for code 4.
Thanks all, as always,
Brooke