Engine 1998-Stumbles when fan kicks on


New Member
Feb 12, 2018
150K miles, dual exhaust, cold air intake. Coolant flushed last year but looks muddy already since before I got it it went 5 years on a change. Ok so. This only happens when it’s hot out like it’s starting to get. Whenever I’m at idle (~750 rpm) and the fan kicks on it drops to about 500 and shakes for a second then comes back up. Surges slightly when the fan kicks off. It’s not bad, I just don’t want this to progress into stalling. It doesn’t have a cooling problem. I know I need a new coil pack/plugs/wires, could this be the problem? Too much energy getting diverted from the aging ignition system when the fan comes online? Help would be greatly appreciated!
  • Sponsors (?)


SN Certified Technician
Aug 14, 2009
Houston Texas
If this were my car I would focus on the alternator and battery. Are the terminals clean and tight? Most auto parts stores will test for free.

Next focus on the quality of the alternator's ground. Here's some information on how to test using the voltage drop method.

Howto perform charging system voltage drop test

After you are positive the charging system is in tip top shape, then check the cooling fan bearings.
Last edited: