1996 4.6L Surges when idling

My '96 T-bird, 4.6L V8 Auto is surging when idling. It will start at 700-750 RPM and surge up to about 1,250 RPM and wave in between there. When its cold, it will also have sharp voltage drops every couple of minutes also. I believe the Idle surging is due to a bad O2 sensor, but wanted to know if anyone else has had this problem. Not sure what causes the voltage drops tho, battery cables look ok when disconnected. This car has 96,000 miles on it, and besides minor problems like this runs fine. I noticed these surges about 2 months ago. Is it something that could cause more problems in the long run, or is it ok to leave it? Don't have a lot of cash right now, but if it could cause major problems, or leave me stranded, I'd rather spring to fix it. Also, has anyone had any problems with the floor shifter? Mine gets stuck every once in a while. Thanks for any help, you guys are usually pretty helpful.

Been having the same issue, both the surging and voltage drops on a '94 V-6. I am thinking of doing the O2 as well, but can't figure out the surging yet. Had any luck with fixes yet?

try having the fuel system cleaned and the electrical system checked.

We have been having similar issues with our 1994 tbird. We also have an issue when cruising (not cruise control but consistant speed) On the highway. It will rev up to 3000+ rpms and stays like that for several seconds or when the gas pedal is released. We have taken it to our mechanic and The ford service dept. and they cannot duplicate it or find anything wrong to cause it. Any help would be much appreciated. It's getting worse by the week.

Thanks.

DKM

If anyone does find the problem plz let me know also. My problem has gotten worse and now it surges at idle, cruising ...... whatever. It does it pretty much all the time. It doesnt seem to do it much when the outside temperature is below 20 degrees. Also, the fast idle does not come on when it's cold. I have replaced IAC valve, TPS sensor, all tune up parts, air box temp sensor, coolant temp sensor and air filter. I'm running out of parts to replace. I now get an IAC code but thats not the problem. Too much moey into the car to dump it so I have to ride it out and get it fixed. Good luck all!!!

Buddy's 4.6 Mustang was doing this and it was the dirty idle air control valve at fault.

Have your codes checked (Autozone does it for free) and let us know what they are.

You may want to check the throttle position sensor. I had this problem myself but it would stall not rev. Replacing the throttle position sensor fixed the problem.

The O2 sensor is a defiant possibility.

i had the same problem with a 95 tbird i took it to the shop and they cleaned off the computer and it ran great

I have a simliar problem with the 4.6 in my Cougar. I wouldn't call it a surge as much as a shuttering. Like a fuel issue. In fact, I think it's running rich when I am at a lite. I have black soot on the rear bumber above the pipes and it stinks. Sometimes while driving it will "bump" like its losing fuel for a second. Never dies, but acts like it might.

I have repl. the fuel filter, the air filter, the MA sensor, cleaned the IAC device, checked plugs and wires. Ran fuel system cleaner thru it. Nothing.
I took it to parts house to have the codes read, the guy there mumbled some crap at me and then reset it. The next day, it came right back on (the CEL). The last thing I am going to try is to replace the vac hoses as I see they look like they are dryrotting.
After that, if it's still doing it, I guess I'm gonna have to break down and take it to the dealer to let them fix it for me.

Anyone with this problem try unpluging the IAC and starting the car. Drive the car and see if the problem goes away. My car runs great now but doesn't have fast idle. Gonna replace the computer and see what happens.