ready to give up

I have set the timing I have replaced just about all the sensors I am still getting a code 21 I have replaced the tps and connector I have sealed the egr no vacuum leaks. I need to know the Idle speed of this 2.8 1986 se. This thing needs to run this is my daily driver. What else could set a code 21 ? is the throttle body just shoot ? I have sprayed carb cleaner every where and no leaks everything is grounded. Idles way high when i set the timing on 10 degrees btc. Maybe I need to talk to a tech I wish I could find some one in Omaha Nebraska to call.

Ok, reading up on a code 21, it indicates a throttle position sensor issue.

 

I don't know how much you know about the tps, but it's a potentiometer. A pot is a device with a fixed resistance between two points, and a wiper which moves between these two end points. In it's normal application, there is a voltage applied betewen the end points, and then the wiper outputs a variable voltage as it moves up and down between the end points. In this way the ecm can tell where the throttle is, and when it is changing etc.

To check if your sensor is bad, remove the plug and measure resistance between A and C. This is the total resistance between endpoints. Remember this value. Now connect between B (The wiper) and C. Vary the throttle position. It should go from a low resistance value at 0 throttle, to very near the value read between A and C at wide open throttle.

If this is ok, then your sensor is ok.

The ecm uses a 5 volt source on the TPS. The grey wire hooked into A on the connector should be +5, and the Black wire should be ground.

 

Find a good ground (Like the - battery post) for your neg voltmeter lead. Disconnect the TPS plug, and on the plug side, measure the A and C terminals. If they are ok, the power wiring from the ecm to the tps is ok.

Plug in the tps. If you have a scaner connect it and watch the tps value as you vary the throttle. If not, strip a bit of wire from the B, or dark blue wire. Connect your voltmeter between blue and ground. Vary the throttle and the voltage should vary too. If you have access to the ecm, check the voltage here too (Pin C13).

 

If all that is ok, there is one more thing. I've heard of tps failures with the resting or 0 throttle position. If the voltage is over .5 volts at rest this will cause the ecm to declare the value bad. Bend the tab of the tps to get the voltage under .5 volts.

 

 

Good luck,

 

Chay

IF you are still having problems u might want to check your MAT sensor. Make sure the black wire on it has no voltage and is a proper ground. The wire for it is shared with the ground for the TPS and will give you the error code. U have to test the wire engine running by sticking a pin in the wire and testing it to ground with a meter. Make sure to electrical tape over the are where the pin was to prevent wire corrosion. i would not be suprised if you have a small voltage feeding back from the MAT sensor...