having problems with cold start and surging.

when you first start the car, surge is pronounced, surging between 700 and 900 rpm at idle during warmup. it doesn't sound like much, but it's noticable.

i give the car at least a 2 minute warmup at coldstart, but it still stumbles a time or two when i first drive it.

the surge is always there, even when warm, although it's less pronounced when the car is warmed up.

plugs, wires, etc are all recent. just replaced the egr valve to get it to pass emissions. power is fine, but mileage is poor: 12-14 in town, 24 on the road.

does anyone have any ideas?

 

It could be a vacuum leak, or maybe your IAC. Your MAP sensor could be bad as well. Are you getting any codes?

 

no, no codes.

aside from the idle and cold stumble, it runs fine.

 

My guess is that you need to have the throttle shaft bore rebushed. Spray some carb cleaner around the throttle shaft and see if the RPM goes up.

 

Beleive it or not my TPS gave me the same problem. It didn't throw a code either. May have something to do with closed/open loop.

At least with the surging part.

With the stumble thing I wanna say check the color of your spark. If your spark looks orange in color you may want to replace the ignition coil. especially if you have over 100k miles on it.

Why? Because the only things an engine has to stay running when it is cold are fuel and spark. When the engine heats up, combustion is assisted through the aid of thermal heat hence the spark plug is not doing all the ignition. some of your combustion then comes from the heat of the motor itself. If you have an "orange" spark, you have a weak spark and may possibly be the reason it stumbles when it is cold and not when it is warm. Your spark should be a blue-ish or purple color. Try it at night. you see it best then.

 

Tell me, what kind of fuel economy are you getting? how many miles per tank? This will help to determine if it is or is not your coil.

 

i'm getting 12-14 in town ..... 24 on the highway

 

sounds decent. Check the color of the spark anyway and tell me what you find. In the meantime I will be pondering what else it could be. I assume this is a 5.0 TBI. correct?

 

yes sir ... 305!

 

I had problems like that it turned out to be the EGR valve.

 

could also be the EGR solenoid. I can't remember what the test specs are supposed to be on a TPS. I know that reference should be 5 volts but, can anyone help me out here? I think his TPS may be bad and I was thinking hard about it, It's not common but, it could be the reason for both of your problems. If I can get my hands on the right multimeter readings I could tell you how to test it to make sure it is not your TPS that is faulty. I know you are checking for resistance but how much I forgot. I think it may be like 2-3 ohms of resistance....Now I need somone to help me. LOL.

 

i replaced the egr valve less than 3 months ago to get it to pass emissions