I am once again FD shopping. Test drove a car the other day with rough idle. However when I turned the headlights on the idle became smooth. The car is bone stock. Any thoughts.

 

idle rpm? vacuum at idle?

Does it have a power fc?

 

if I remember correctly it was pulling aroung 15-16 on idle. Idle between 900 and about 1500 when rough. Car was bone stock with the exception of an aftermarket intake.

 

When the idle is at 900, verify the engine vacuum. Also check to see if the needle is bouncing rhythmically.

It may just need plugs/wires or have a leaky injector...... or it may have a chipped seal or internal coolant issues.

When you give it electrical load the idle bumps up, which gives better vacuum and can give a smoother idle.

 

Does it have the airpump removed with this aftermarket intake?

 

Unfortunately the car is up in Mass and it wouldn't be practical to go to Jersy pre-sale. Also engine has 72k on a rebuild 144k on chasis. Normaly wouldn't even consider this if it wasn't a CYM and fairly clean.

The idle was bouncing rythmically.
I figured it was

1) Coolant or seal issue(engine)
2) Vacum Leak

I suspect if it were an ez fix, like the plugs, it would have been done already.

 

Ok is the idle rough or just bouncing?

 

What's the difference!

 

Do a compression test. Thats a lot of miles for a rotary.

 

One sounds like it's struggling to stay alive and one is rhythmic. When I had a boost leak it was very rhythmic, consistent. UP slowly down, UP, slowly down.

Turned out to be a hole in one of the plastic tubes and a blown LIM gastket.

 

Sorry, should have clarified-----at a steady rpm check to see if the boost gauge (vacuum) needle has a rhythmic 'tick' to it.