I own a 98 crown vic police car that has about 100,000 miles on it. We have owned crown vic police cars for 15 years and have never had a problem like this one, and can't figure it out. This is such a complicated explanation. It all started with me letting the car sit and run one day for about 45 minutes or so. I then got in it to drive it and it would not go over 10 miles an hour....took me 45 minutes to go about 5 miles. We figured out that it was the Mass Air Sensor...replaced it....and it ran fine again. Until about 2 months later. (we didn't drive it much over those 2 months because we were on a long vacation and also it is the summer and I don't do alot of driving when the kids are out of school). It hadn't been running very good anyway. It was giving me a lot of trouble when I was trying to fuel it (may of may not have to do with the problem---and actually it wouldn't take gas right from day one that we bought it so this was not new), it had a little shimmy when it was in park and idling, and then most of all occasionally it would start to cough around and the check engine light would come on and flash at me...during which time it would run terribly. Then I was sitting at a stop light, (car running well at the time), and some chick wasn't paying attention and ran into me. Not too hard...but enough to jolt me forward....and the car actually died. It actually started right back up, but really ran bad after that. I pretty much took it back home, and haven't driven it much since then. We have tried several times to fix it, and each time we have thought that we had fixed the problem. It will run well for several minutes and then start all over again with the same thing. So here's some of it's symptoms.
--It seems to run fairly well when it is running and in Park, (while idling), with only a little 'shimmy' every couple of seconds.
--If it is idling while in Drive, (like at a stop light, or if you are like in a line and have to let off the brake to coast up a little and then reapply the brake), it coughs and carries on like it is going to die. If you put it up in Park while it's doing this it will resume almost purring like a kitten...except for the little shimmy.
--When you are driving it at low speeds...like under 35 or so...it does the thing where it is acting like it is going to die. If you give it more gas...or get it up and stay up in the over 50 or 55 range....then it seems to run pretty decently.
--Also, while it is coughing around and acting like it is going to die, (either at low speeds or while idling while in gear), then the check engine light flashes on and off continuously.
--Back a couple of months ago we thought it was fixed and I drove it to town...so pretty much of the time I was driving it at low speed. It acted like this so much that I actually felt the floor hot. I pulled over and looked underneath and the exhaust was glowing. My husband cut off the front cadylitic converter and after replacing all the exhaust again the second one glowed later when testing. Since then he has taken the exhaust all apart and checked everything out, and cleaned/replaced all the oxygen sensors in the exhaust too....nothing was clogged there either.
--He has checked to make sure it wasn't a timing issue. It doesn't appear to be.
--He has checked to make sure the coil packs are all ok...they appear to be.
--We have had it on a machine with no success. The only code it ever threw was some kind of idle control thing, (I can't remember what it was called), but we bought it and replaced it too. It acted like it was gonna fix it, and then went right back to the same stuff again.

I feel like it is important to note that it does run. You can drive it at high speeds and it will really get. But it has the ‘shimmy’ all the time. And at around town speeds it acts like it wants to die…but then doesn’t. When it gets a notion it will start really hesitating and jerking and coughing around and then it doesn’t want to go at all. This is when the check engine light flashes on and off. All other times the check engine light is just solid on. I know this isn't a very technically worded request, but I just don't know what else to do besides to just describe what it is doing. Maybe somebody out there will have an idea that we haven't yet tried...

ANY IDEAS?? PLEASE HELP!!

 

What kind of machine was it put on? If it was a scan tool to check codes, then it may not tell you what the problem was. Have the plugs been changed? You said the coils were good, how were they tested? You can have a cylinder misfire and not have a code come up.