Different RPM's

Update:
Had the computer on it today. Said it was a bad or going bad IAC. Was only opening up 43% at 1000/1500/2000/2500 rpms. Will replace tomorrow and run it. Hopefully that solves it.
Both motors had no faults recently or in their history.
 
Save a dime and try carb cleaner in the IAC.
Mine are 2001. Looked like new when pulled but still sprayed them. Now they work like new.
 
i am confused (which is not uncommon these days).....how would a failing IAC valve cause a drop in rpms while at cruising speed?.....I thought the IAC valve only affected the engine while at idle.....

cliff
 
i am confused (which is not uncommon these days).....how would a failing IAC valve cause a drop in rpms while at cruising speed?.....I thought the IAC valve only affected the engine while at idle.....
I am too. I literally saw the computer screen myself. The “theory” is if it doesn’t open all the way up when underway then the motor isn’t getting the necessary air flow. We’ll see what happens today.. I personally think there’s another issue beyond this
 
In the meantime, I'm troubleshooting a mis-fire on my V6 sports car. I changed all the plugs first, and am now looking for a bad coil pack. I'm really surprised how little difference there is at idle between a V6 running on 5 cylinders or on FOUR! I'm glad it's not a V8.
 
For the car, is the check engine light on?
A code scan will show which cylinder is misfiring.

There are scanners readily available for much less than $100, or get a free scan at autozone.

I wish marine engine scanners were that inexpensive!
 
The code it's throwing is "random misfire", and I don't want to risk a cat-conv by driving it to Autozone. Hence the trial-and-error. If I come up blank with the coil packs, I'll buy a scanner. (prob should anyway)
 

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