I have a Dodge Daytona but my daughter drives a 98 Neon. I am always the one she comes to first with a problem. Sometimes I can help her. But this seems very strange to me. Her cars idle jumps significantly when she turns on the fan (heater/ac) . I also noted that I could hear her A/C compressor cycling. We were not running the ac when this occured. My first thought was the idle position sensor, but I have never thought there would be an asociation with the blower motor fan. Is this a common problem with the Neons? If you know of this please enlighten me, so I can look like a hero to my daughter again.

Thanks John from Calgary AB

 

Def. could be a TPS, when you turn on the blower motor, the PCM compensates for the extra load on the alternator, it may be over compensating.

 

Thanks for the advise- I have had trouble with the TPS on cars before but I never saw it like this. The RPMs must jump by 500 (she has no tach) I will try changing out the module. When I hear her A/C compressor cycling at idle when running the heater is that just an indication that her coolant (freon) is low?

 

The compressor cycling means it's time for a recharge. The kits aren't all that expensive. The A/C kicks in to dehumidify the air when the selector is on defrost. When the A/C kicks in the radiator fan turns on to draw air through the condenser. With the increased load from the compressor and load on the alternator idle is adjusted up accordingly.
A bad TPS will cause poor acceleration or stalling when you step on the gas. It doesn't determine idle speed as far as I know.

 

Thanks, I will try a recharge before changing the TPS, when I had a problem with the TPS before it had a noticable effect on the way the car ran as a whole. I don;t think that is the case. So I will give the recharge a try.
John