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Discussion Starter · #1 · (Edited)
Since the weather warmed up, I've been experiencing rough idle and stumbling. When it's cold, it seems to run just fine; after a bit of driving though, it starts idling funny. Driving at night doesn't seem to be a problem at all, when the air is cooler. The Air Conditioner seems to bog the engine down even more. The car has 95,000 miles and the following have been changed:

Idle Air Control Valve
Throttle Position Sensor
Air Temperature Sensor
Coolant Temperature Sensor (both the water pump and engine sensor)
EGR Valve
Vehicle Speed Sensor
MAP Sensor

Prior to changing the TPS, the voltage reading was .62v; with the new TPS, it's .72v. The IAC counts start low, around 10-20 at start, drop down to almost 0 when it's in drive at idle. RPM's bounce between 650 and 750 at parked idle; and drop to between 550 and 700 idling in drive.

I've checked the MAF sensor and confirmed that it is working correctly; I've also checked for vacuum leaks all over the engine. I've read about the ICM or the OptiSpark causing issues with idle, but am hoping it's something easier and "cheaper" than either of those!!

Nothing else is modified or adjusted.

The other item I noticed, using a MT-2500 Snap on Scanner, during the transmission scan, it displays a vehicle speed exactly half of the true speed. Under the engine scan, it shows correct speed, but transmission shows exactly half. From what I read on other boards, the VSS can affect idle as it sends info to the PCM for the IAC.

Rather than throw more money at it, thought I'd see what others might have experienced. Any help is certainly appreciated. :thumbsup:
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