Dropping RPMs

pepito6SC

Registered User
I finally got my car running after 5 months. I am very happy. Everything runs good except for this...

1. When the fan starts up, the engine's RPMS drop about 500 rpms and then it recovers. This happens every time.

2. When the steering wheel is turn ALL the way to the right or left and held there the engine's RPMs drop about 250 rpms until you let the streering wheel go.

and

3. If I rev the engine to about 2500 rpms from idle and let off the throttle, the engine's rpms drop about 500 rpms below idle and the recovers.

The car idles fine and is not overheating. any ideas on what is causing this? Thanks!
 
I have a similiar problem and am searching for a solution as well. My idle dips whenever I shift into reverse, and whenever I turn the wheel from a standstill (so basically whenever I have to back in or out of a parking space!) I was considering upgrading to a more powerful alternator, as I think I remember reading once that is solved similiar problems for another SC...
 
Sometimes a normal load on the engine will cause this, but many of these exact things occured when my throttle position sensor was starting to fail. It did not throw a code, and it wasn't a complete failure. I unplugged it, and the problem was exasperated. I replaced it after plugging it in and getting a code for it, the problem disappeared. I estimate the sensor was dying for about a month.
 
Check your motor mounts as well. Not sure about the fan causing the revs too drop. It's a good idea anyway as the stock units are a common failure item.
 
Engine RPM's dropping

I think this is common in any car. When your fan turns on, it draws a huge current taking away from the ignition.

Your reverse lights come one drwing some current from the ignition.

You rev it and let it go back to idle, your RPM's drop below 750 and then recover, I think this would just be the engine *finding* itself to sit back at idle.

This is just my 2 cents. As a former electronics engineer student, the electrical parts of my explanation make perfect sense in theory.

My girlfriend has a brand new Mustang and it does the exact same thing (except for the reverse thingy:) )
 
I had the exact same problem. Low idle when put in reverse or drive, got worse when turning the wheel, and drop in rpm's everytime the fan came on at a stop light or when idling. Was driving me crazy to the point I hated driving the car. Had the car tuned up which did not help and cost an arm and a leg. Had the codes checked and everything came up normal-code 111. I know your not going to believe this, but I cleaned out my throttle body and butterfly with STP Throttle body/intake cleaner just yesterday and the car runs fine now with no more erratic RPM drops. I would try this before changing the throttle position sensor or the alternator. Good luck. TB
 
Plus it sounds like maybe a better alt. - at least 130 amp - may also improve this situation. (Plus it would be good for stereo, brighter headlights, etc.). Man, it would be great to get rid of that dipping idle, shudder, reverse turning scenario!
 
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