95 SHO strange idle

Guys, My 95 SHO has been running great for a while now but I notice that while at Idle it speeds up from like 750 RPM's to about 1000RPM's w/o a reason. It really feels like if the car was just idle and I turn on the A/C but I dont. Any ideas what could be?

:banghead:

How's your fuel economy? Are you using a washable oiled air filter? A dirty MAF sensor could cause this, an Intake Air Temperature (IAT) or Coolant Temperature sensor that is not reading accurately could contribute, a vacuum leak could be at fault, or a slow or failing Idle Air Control (IAC) could be your issue. I suppose slow oxygen sensors could contribute as well.

I'd start by making carefully cleaning the MAF sensor as that will either have no effect or at a minimum improve fuel economy (assuming you don't break it in the process). There have been numerous posts on this forum relating to cleaning the MAF, so I won't repeat them here.

If you have access to a scan tool with datastream mode, get into the datastream and monitor the various sensors and see if they are operating like they should or giving reasonable temperature readings.

-Rod

I replaced both, the MAF sensor and the O2 sensors not too long ago. Economy seems to be average to the kind of car it is. It only runs with premium gas. I was told that maybe a faulty Throttle Position Sensor. Whats your take?:2cents:

If you have a multimeter the TPS would be easy enough to test. Backprobe the ground and wiper wires for the TPS with your meter set to read DC volts. If it's not an autoscale meter, then select a scale that will give you at least 0-5 V full scale swing. Slowly and smoothly open the throttle from closed to full throttle and verify the voltage tracks linearly to the opening and closing of the throttle. At closed throttle you should only see a few tenths of a volt. If you see something close to 5V, then you are on the reference line instead of the ground. That's fine, your voltage readings will just be a negative slope rather than a positive slope. If the voltage doesn't move at all, then you are probably on the reference and ground wires. Move one of the probes to the third wire. IIRC, the wire colors are green, orange and black. I think you want to be on the black and green wires.

Since your problem is at idle rather than while driving, I would not immediately suspect the TPS as the problem since it would be sitting stationery. If you had a glitch when accelerating, then TPS would be a likely candidate.

You may want to pull the intake air hose off the throttle body, open the throttle plate and see how much carbon is on the back side of the throttle plate and in the throttle body. If there's a lot of carbon, then cleaning the carbon out may help the situation. I've been quite pleased with how well the STP Throttle Body Cleaner spray works. Be sure to wear your safety glasses though.

-Rod