Hey guys, when the engine of my 91 Accord (MT, PGM-FI) is warm my idle drops beneath the 500rpm and the engine runs awful when stopping the car at lights for example. If I then run also the AC it's getting more worse.

It needs a few seconds until idle comes into regular regions, but after a few seconds its dropping again.

I already cleaned the fast idle valve unit, with no success. I found that there's an additional air valve which is controlled by electronic and not by water, may this valve be the problem? Will it help to clean it too?

Or is there maybe another thing I can check...?

 

Spark plug gap could be to wide.
Throttle body could be dirty. If wiped clean inside, make shure not to unhook the throttle cable by mistake.
Check if the airfilter isnt too dirty

 

Cleaned the throttle unit and the additional air valve, now it's working again
Thanks!

 

Air valve? Is it by the throttle?

Thanks.

 

Yes, it's directly beside the regular fast idle valve assy.
Whereas the fast idle valve is only controlled by water the other one is controlled by both water and electric.

It looks familiar to the other one, but it has a very small tiny filter in one of the holes which was pretty dirty on my one, thought that this was the main problem.

 

Well the problem has really improved, but sometimes the idle's still dropping beneath a value on which the engine become running roughly....

Is there anything else I can do? Spark plugs are in great condition, air filter is also not dirty.
I guess it's not possible to alter the rpm or to raise the iginiton to get it a bit higher right?