Major RPM drop when engine fan comes on.

[John Smith]

Hi Guys,

Recently when the engine fan comes on it causes the engine RPMs to drop dramatically at idle (down to 500 RPM before returning to normal) The car has always dropped RPM when the fan comes on, but not to this extent. Also, when the idle drops the fuel pressure kind of goes crazy; It goes up to over 50 psi and then drops down to 20 and then goes up to 35 before stopping at 30. I am guessing that the electrical surge that seems to be happening is effecting the fuel pump and or Boost a Pump. Any ideas? Alternator getting ready to take a crap? Battery?

Thanks,

 

[stangGT97]

I'd say take your car to autozone and have the alternator load tested, and have the battery checked as well. the voltage regulator in the alternator may be crapping out. I noticed my car doing that too, no biggie, just kinda gets on my nerves

 

[sgarlic]

I like your thinking. I'm a major supporter of the notion that electrical gremlins can cause other problems.. i.e. fuel, etc.

I think it's definately a possibility that a battery on the way out or an alternator may be at fault.

I would start with a simple test, if you have a multimeter, just test the voltage of your battery with engine off, and engine on.. if it's norm with engine on, shut it off, let it sit for 10-15 minutes, and see how much it loses. If it's a lot, like from 13v to 12v, may be time to replace the battery. The voltage you measure across the battery with the engine on is basically what the alt. is putting out. I don't know the exact spec, but consider mine is around 14 something. A good condition stock alt should be putting out at least 14 at idle.

 

[sgarlic]

I also forgot to add that a far simpler idea would be to remove and clean the IAC. I recall threads from way back where people had this sort of problem, and it turned out the IAC was full of carbon and not doing its job (which apparently under those circumstances is to help the idle stay somewhat normal when big loads are placed on the engine.)

 

[NO BRAKES]

I would say check the alternator and battery... stangGT97 has a cheap way of testing.. take it to A Z.. I dont like their parts but hey when the testing is free.. do it!!

 

[John Smith]

Thanks Guys

 

[2002GreyGT]

If I remeber right from my car audio tuning days, the alternator should be at 14.4v when running. Anything above 14 should be ok.

As for the IAC, I got a new one for like $25 or something and now the car idles much better. Simple 5 min swap out job.

~K

 

[JohnnyG3]

Did you ever solve the problem? I’m having same issue.