Increasing the idle rpm

[Porthos]

I have an M40B18 that recently got a 90amp alternator attached because the original 65amp is no longer being made. It is idling a little rough not bad like it is going to stall it is just having a little trouble idling low and still spinning the alternator. Is there a way to raise the idle up about 250rpm without having the ecu kick it back down?

[nando]

Idle speed is not adjustable.

if it's not idling nice, you could have a vacuum leak, dirty injectors, misadjusted TPS, sticky ICV, etc. Even with the extra load of the alternator, it should still idle at the target idle speed of approximately 650-700rpm.

[CRBR30]

Yeah you probably have a vacuum leak. I have one right now lol. Try cleaning out your ICV with carb cleaner, if it doesn't help then you have a vacuum leak.

[Porthos]

Thanks guys. I will give that a try and see what happens.

[AndrewBird]

The alternator won't put more load on the engine unless you are drawing more amps. I.E. - The amperage rating is a max capable rating, not a constant output. Current is always drawn from a source, not pushed from it.

In short, you have another problem unrelated to the alternator.

[Porthos]

Yeah it came stock with a 65 amp and now it has a 90 amp.