Throttle Position Sensor-need help

1990-oldsmobile cutlass supreme
@110 thousand miles
3.1 v6 FI

Im having idle problems, just replaced the IAC Valve, runs a little better but car continually gains speed with no pressure on the gas in drive and does not hardly decelarate when braking, startup is shaky and idle fluctuates, before replacing the IAC have to press gas just to get it started. thinking throttle position sensor. any advice?
IAC=idle air control valve
Check engine light does come on at when idling for a minute or so.

Check for a vacuum leak. Especially around the intake manifold. The gaskets on these cars are crappy. If you have a leak around the sealing surface it would display all the signs you are mentioning. Also check and make sure you aren't getting any water in the oil as that is also a sign of bad gaskets.

Any way to check for water in the oil or oil in water? i drove it tonight and its almost like powerbraking just to slow it down. does seem like a vaccum leak. im going to check for the leaks tomorrow. will update

Pull the dipstick and look at the oil. If it looks like chocolate milk then there is water in the oil. As for oil in the water, pull the radiator cap and look at the coolant. If it is brown in color or there is a brown sludge on the top of the coolant there there is probably oil in the water. You will probably find water in the oil before oil in the water.

1990-oldsmobile cutlass supreme
@110 thousand miles
3.1 v6 FI

Im having idle problems, just replaced the IAC Valve, runs a little better but car continually gains speed with no pressure on the gas in drive and does not hardly decelarate when braking, startup is shaky and idle fluctuates, before replacing the IAC have to press gas just to get it started. thinking throttle position sensor. any advice?
IAC=idle air control valve
Check engine light does come on at when idling for a minute or so.


If the vehicle keeps speeding up (like surging) when your are applying your brakes or even on crusing mode, more than likely it is the TPS itself causing this problem. The TPS is used by the computer to monitor the throttle position and adjust the speed, fuel, air, etc accordingly to match the throttle position. If the TPS is bad and just move by itself constantly then the computer will have to adjust itself to compensate of the current throttle position. TPS is not cheap, you can test a known good used TPS from a junkyard to test it.

IAC is different from the TPS.
The IAC has some spring in it while the TPS which located on the same area as the IAC is just a small device like the size of a quarter.

did not see any vacuum leaks...cars RPMS are around 10k idling and it sounds like it wants to die, i was going to take off the top prtective plate but this car is a maze of fuel lines, i did notice that the throttle piece itself seems to be leaking some air. but thats prolly normal...all these problems started about a week after i sprayed the engine down with deagreaser and sprayed it off with a water hose in an attempt to find a oil leak...could this be the cause of the problem? i am taking it to the mechanic later on this week. will update.

If the vehicle keeps speeding up (like surging) when your are applying your brakes or even on crusing mode, more than likely it is the TPS itself causing this problem. The TPS is used by the computer to monitor the throttle position and adjust the speed, fuel, air, etc accordingly to match the throttle position. If the TPS is bad and just move by itself constantly then the computer will have to adjust itself to compensate of the current throttle position. TPS is not cheap, you can test a known good used TPS from a junkyard to test it.

IAC is different from the TPS.
The IAC has some spring in it while the TPS which located on the same area as the IAC is just a small device like the size of a quarter.

You may have your IAC and TPS backwards. The TPS is spring loaded, about the size of a quarter, and can not move by itself. The IAC is not spring loaded and moves by command of the PCM. The TPS will generally only make the engine hold a specific RPM. Such as it will always want to idle at 2,000rpm, not so much surging although it is certainly possible. The TPS is also not expensive, for that car it's about $30.

If pressing the brakes affect the engine speed I would lean towards a vacuum leak. The brake assist uses vaccuum and activating it may be setting off the engine. Unmetered airflow into the engine will cause it to run lean, the PCM will compensate by closing the IAC but almost always overshoots, so it will go rich, and compensate again. Thus the surging. It's mostly due to the erratic nature of a leak, but a narrow band o2 isn't an exact sensor.

Hook up a vacuum gauge. Look for low or erratic readings then comes the searching. Good luck.

the problem of the car picking up speed and not wanting to slow down has stopped and no idea why, the other problems though still exist.... i checked the linkages cause i have had the coil pack replaced and i have a small oil leak on the front right side if you are in the drivers seat... it did leak oil down into some of the connections and one in particular,on the bottom right of the car that looks like a small metal canister the conecter was coated with oil and the receptor too...cleaned them both but would they have anything to do with it? and i found a blown 30a electrical fuse in the electrical center inside the hood....maybe the problem?
also the oil is fine, not milky

I was not clear with the TPS and IAC. The IAC itself has the spring visible outside. The TPS is located near the IAC. TPS is the size of a quarter which you don't see the spring outside though because its spring is located inside itself.

i pulled the cap off the fuel pump relay under the hood and the fuse was blown. i think the problem is solved. thanks for the help though.