hi rpm when starts

when you first start engine it runs at 3000 rpms for about 15 seconds then back to 500. is it a sensor it is a 1990 4.0

map sensor , dont buy a cheepie , get an OEM part , check the vacum line first , could just be disconnected

There is a relay that keeps the power to the ECU for a few seconds after you turn off the engine so the ECU can reset the Idle Air Controller back to a "start" condition. If it is bad, you will get a high rpm start until the ECU brings the rpms back down.

I can't remember the name at the moment. It is something like ASD, automatic shutdown relay. It is in the row of relays next to the battery. Swap them around to diagnose.

old_man said:

There is a relay that keeps the power to the ECU for a few seconds after you turn off the engine so the ECU can reset the Idle Air Controller back to a "start" condition. If it is bad, you will get a high rpm start until the ECU brings the rpms back down.

I can't remember the name at the moment. It is something like ASD, automatic shutdown relay. It is in the row of relays next to the battery. Swap them around to diagnose.

Click to expand...

yup-- that's the one^^