tickover drop

[johnf]

When I come to a stop my tickover rests at about 1200 but after 10 / 15

seconds it drops to around 800 and obviouslyit\'s not as smooth.

Does anyone know if this is a sympton of anything or should I just adjust the

tickover up to compensate this drop.

Thanks

John

[Brett]

Tickover on an FC should be around 750-800rpm.

If it\'s higher it means someone has been tweaking it - probably to hide a rough idle. (Do you have a ported engine, can\'t remember?)

Does it run smoothly otherwise?

[johnf]

Hi Brett

Stock engine - not all that smooth at 800

fine when driving - best it\'s ever been

Thanks

[TiddlesRX7]

Maybe the BAC valve needs tweaking or taking off and cleaning if its sticking. Or failing that maybe the throttle cable is sticking slightly.

Ade

[Brett]

I\'d suggest the cold start assist is up the creak, and as a result the idle is sitting at the cold start point all the time.

At 800rpm is it a rough idle, or a bouncing idle? (as in does it sound like its missing at 800, or do the revs hunt?)

[johnf]

I would descibe it as rough, although that may exagerating, certainly not as smooth as my FD used to be.

I\'ve also noticed that the revs drop slightly when I turn lights on, never noticed that before.

[TiddlesRX7]

That sounds like its bac valve related then if the revs are dropping when the light get turned on. The bac should up the revs to cope with the extra electrical load.

[johnf]

Thanks but can you explain \' bac valve\' in pretty basic speak and what if anything I could look at doing/checking.

thanks

[Prof]

TPS and timing - you need to set the TPS when the engine is warm - and it\'s a bugger to do because on the stock TII you have to remove the intercooler and that loses you some heat out of the throttle body, meaning you never quite get it set.  Then with the test jumper shorted, you can set the idle (the test jumper prevents the electrical load adjustment on the BAC), and also the timing.
 
After two or three iterations the idle will be quite smooth at 750-800.  I\'ve had to adjust the small screen in the AFM (well under it) for final adjustment of unmetered air.
 
Of course none of this works at all well if there is even one air or vac leak, and that can be a bugger to track down.

[yasiryassin]

http://i32.tinypic.com/1z4ctpc.jpg
screw at the top right is the adjuster screw for BAC.
 
Maybe worth while adjusting the idle control screw also a tiny bit to bring up the revs a tiny bit. will probably smooth the idle.
 
then TPS will needs set up again.
 
worth while checking the timing with a light gun also if you have one. just incase.

http://img90.imageshack.us/img90/2405/dsc00165te8df4.jpg
this is where the BAC valve is just incase your not sure also

[yasiryassin]

http://www.rx7club.com/attachments/2nd-generation-specific-1986-1992-17/339211d1239512082-rich-idle-afrs-hesitation-87-tii-rtek-2-1-stop_screw-jpg

that is the idle control screw i mentioned, this is a poor picture tho. but hopefully should give you a good idea.

the screw should be touching the linkage. the more you screw it in, the higher the revs will be. only need to make tiny adjustments to that screw.