warm engine surge?

[Mike J.]

Hello,

when the car is cold it starts and runs smooth. When I drive it and park for a few minutes (running into a store and back out...5 mins) , the car starts.. surges about three times and then smooths out. The surge will be about a 500 rpm swing. If it is severe enough it will surge once and then stall the motor. It always starts back up fine, but will do the surge and then smooth out.

At this point the car runs very good once it smooths out and drives down the road just fine.

There is no warning lights lit on the dash or anything. I've found a few posts talking about engine surge , but none that really laid out what to look for.

Any Ideas?

Thank you
Mike J.

[1990LTD]

Try cleaning the IAC valve. IAC = idle air control

It's located on the back of your throttle body facing the firewall, and it regulates how much air gets past the throttle blade when you're not giving it any gas; they get pretty gummed up with carbon after many years of faithful service.


If you clean it, make sure you clean out the throttle body as well, since it will just get dirty that much quicker if you don't. Replace the gasket between the IAC and throttle body if need be


No guarantee that this is the problem but it's a start. Probably wouldn't hurt to clean (I use Seafoam, YMMV) the intake and inside of the throttle body/throttle blade as well

[famcrown]

in regards to cleaning the egr valve, what is the best way? i recall s/o told me only to spray carb cleaner on 1 part??

also there is a sensor or valve or s/t which plugs into the engine- directly beneath upper manifold on the drivers side.- its right near the altenator.. -- what is that and how should it be cleaned.

[gadget73]

sounds like its switching from closed loop to open loop and getting wonky when it does so. You should not be able to tell when it does this if things are working right. How old are those oxygen sensors? If they are giving strange readings, it might make the ECM panic with a sudden and incorrect fuel mix adjustment.