wont idle & runs rough when heater is on. also speedomp. has gone haywire dont know if its related or not.
Feb 7, 2010 at 8:14 AM
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DENNYP
CERTIFIED EXPERT
1,824 POSTS
The speedo problem is most likley a bad instrument cluster. As for the rough idle, the heater should not affect on the idle quality. If it is in defrost mode, the A/C compressor will cycle. This will have an effect on idle quality.
The first thing to do is have it scanned for trouble codes. Use a scan tool to see if there are any cylinders misfiring.