Engine rev when in park

[howlingwind13]

When I fire up the car and it is in park the engine starts revving. From about 5 to 15. The lower it drops the higher it revs.
Sounds like someone is pushing the gas pedal then letting off constantly...the fuel pump would also run for about a minute and if you tried to start the car before it shut off, it wouldn't start.
A friend said to change the rpm relay...which I did...and the problem stopped for about 2 weeks...now its doing it again.
Fuel pump cuts off after a couple seconds and the car starts, but just revs
Any one else had this issue?
mike

[David T]

I don't think you are describing the problem well. With your foot off the throttle pedal and the pedal all the way to idle, and the car in Park, you say it revs up and down by itself? Then you are saying you have a problem with the fuel pump and a 3rd problem with starting it. To begin, you have an automatic and does it still have the K-Jet fuel system? Has it ever run right? What have you done to it besides the RPM relay?

[howlingwind13]

Okay I will describe it better...
When I start the car, after it is sitting idle in park for about a minute, the rpms start fluctuating between 5 and 15 if it drops below 5 it jumps to like 20. It does this constantly...like someone is just revving the motor...I can try and take a video tomorrow.
But as stated I was told the rpm idle relay needed replacing, which solved the problem for a week or so. But now its back. It is the original motor but has been rebuilt.

[Ryan King]

That's called "Hunting"

A very common DeLorean...erm....characteristic? Its very normal.

Let the car warm up and see if it stops. The car needs to warm up and idle hunting should cease for the most part.

EDIT-: Also, the exhaust system has an "Open" & "Closed" loop system, which adds to the hunting idle you are experiencing. Maybe another member can explain it better, but essentially the system has to warm up, thus, open loop. Once its warmed up, it falls into a closed loop. Its weird and hard for me to describe. You can take a video of what youre experiencing, but I'm pretty sure its what I stated above.

[Ryan King]

Is it something like this?

https://www.youtube.com/watch?v=4FEjgP0si2U

[David T]

Reving when cold without touching the throttle is normal, racing from 500 to 1500 is a lot but not terrible. It should level out to a much smaller amount quickly. How is it once the motor warms up?