surging in park

After searching about surging, my question about this still needs an answer. I have a 98 SES 3.0 Vulcan with 102K. It runs just fine, however on occasion after driving it for a while, and then parking for a short such as at the store, the engine will drop from normal idle to about 100rpm and return to normal idle (will do this several times) or stall out immediately after starting the car. If I rev up the engine when it first starts to drop off, its fine and no more surging occurs. There is no surging when driving the car in all speeds. I did notice this morning on the way to work in the rain, it started to stall out on me at a right turn. Hasn't happened since, but I'm getting the feeling that this is a condition that will continue to get worse. I initially thought it might be bad gas, or water in the gas, but I use ethynol gas and have not had any problems with water in the gas. I have thought maybe a can of fuel injector cleaner might be in order, but usually I only have to use this once a year. Any suggestiosn would help. Just a little back ground, I did repalce the EGR and DPFE(?) this past summer. Mileage is good at 19-21 arount town.

You mention you usually only HAVE to use fuel injector cleaner once a year. What do you mean, HAVE to? As I started reading your post and formulating an answer the first suggestion that came to mind was to run a bottle of fuel injector cleaner through the system. I put a bottle in at every oil change, so about 4 times a year. For $2, it's good preventive maintenance. I think the label on the bottle recommends something even more often, like every other tank full of gas or something, but they are interested in selling product. I'm just interested in preventing problems. I'd suggest starting with a bottle of cleaner and seeing if that has any effect.

Does your '98 have a distributor cap and rotor, or is it distributorless? If you have a cap and rotor, they could be the problem, especially since you noticed the problem was worse with the wet weather. If the injector cleaner doesn't seem to help in the first 50 miles or so, you may want to pull the spark plugs and inspect them, and maybe even replace them and the wires.

Thanks for the response. I guess I shouldn't have said "have to" concerning the fuel injector cleaner. I usually put one bottle a year in when I change the fuel and air filters. It is an electronic ignition system and the plugs and wires seem in good shape. The surging occurred primarily right after drving the car for a while, weather wasn't a factor until the morning. Still not convinced rain is effecting this as much it is something that started to occur and is gradually getting worse. But I will pick up a bottle of fuel injector cleaner and go from there. The plugs will be next to check. If I recall I replaced the plugs and wires about 2 years ago.

I have a '92 Escort that had the same surging problem. It only occurred at idle. Turned out to be the mass air flow sensor........a piece of cake to change out and very inexpensive at about $15. Hope this helps.