I know what your thinking another rough idle thread. I have a 2000 GT. It idles a little rough, not to the point of a misfire, and no CEL light or codes. Every once in a while the RPM's will drop and then go back to normal 800 RPM. I already changed all the spark plugs, cleaned the IAC valve and throttle body. Any suggestions would be appreciated, i don't want to go easter egging and just changing out parts to see if it fixes it.
Rough Idle
- Thread starter MPScott1
- Start date
-
Sponsors (?)
I have been putting the low grade fuel, jus filled up using 89. I checked the coil packs when i did the spark plugs, they looked good except for the rubber cracking at the bottom. Not sure how to test the coil packs, how do you test them? The car doea seem a little sluggish too, does seem to be getting all the power from the engine.
Thats what i was afraid of, probably jus buy a couple here and there since they aren't cheap. I was thinking about getting an IAC and try it out see if it helped, and if not just return it. Was just running my car for a minute and noticed a sort of rattling or grinding noise from underneath, and it went away when i pushed my clutch pedal in. So i dont know what that could be since the new clutch kit was installed 2 weeks ago.
I have only had the car since November and haven't changed them don't know if they were changed before or not. Since my last post i replaced the IAC but still having issues. Just sitting in my drive way with the car in neutral i revved it to about 2500 RPM and pushed the brakes, the rpms dropped down to almost 500 and the engine was idling real rough, when i released the brakes the RPMs went back up. So i have no idea what the issue is, its getting frustrating though. I don't think its anything to do with the ignition coils or spark plugs, because with it running i unplugged each coil one by one (unplugged it for a sec plugged it back it and went to the next) and the engine ran worse after unplugging the coils.
wmburns
SN Certified Technician
^^^ The RPM's dropping when pressing on the brakes is a function of the hydro-boost. The power steering pump is applying a load to the motor.
FWIIW, most any motor will run rough if the idle is too low.
Consider that the Mustang's does not take power steering load into consideration when adjusting the idle. It's normal for the idle to be slightly low when setting at a stop with your foot hard on the brake.
It's also normal for the idle to "hunt" slightly due to a rapidly changing idle motor load. That is the IAC doing it's job.
The difficultly here is separating what's normal from what's not.
IMO it's normal for the idle to drop when standing hard on the brakes at a stop. But the idle should return to normal levels after a short while. This indicates that the IAC is doing it's job. What would help the trouble shooting is to "know" what the IAC duty percentage is and to see how the PCM is changing it. An ODB2 scanner is needed for this.
Regarding the COP boots. It's possible to buy a complete set of just the boots for less $$'s than the cost of a single COP. Check out Autozone (Duralast).
Has the battery and alternator been tested? Are the battery cables clean and tight? Don't cut corners here. Almost all auto parts stores will test both for free.
How does the car drive when moving? How's the gas mileage? If both are good, them maybe the ignition system is OK. And maybe some other "adjustments" are needed. Perhaps up to and including the "driver mod".
Last edited:
Similar threads
