Help please

[905.0GTford]

My car is a 90 gt 5 speed, the other day I notice the check engine light flicker
and went out, the car ran fine. The next day I went to a friends house and it ran fine came out about 15 mins later started it and the engine light came on
and the idle went up and down by 2-300 rpm's. The idle was up and down real fast. When I came home I scanned it and code 34 came up.
it has a new EGR position sensor so i replaced the egr valve erased the code started it up and the code was gone and the idle was great..........for a minute then it starts with the same idle and the code came back. All the searchs I have done indicate that it is the egr, since I replaced mine what do I look for next. This I believe is a sensor that is causing it but which one.

 

[ss93cobra]

Is it getting vacuum?

 

[905.0GTford]

I don't know, at what point in the warm up process should it get vacum. I am not fimilar with Fords at all I have always had Gm cars. The car has a new crate engine and everthing on the motor is new. The code 34 states three possible things it could be. I hoped that the egr would do the trick, looks like I will have to take it to a shop

 

[HISSIN50]

EGR functions at part throttle (Cruise). it does not function at idle (at any time), nor when the motor is cold, nor at WOT (warm cruise basically is the time when it should be functional).

with a new position sensor and valve, assuming the sensor is calibrated to the valve's seat, i would check some wires. IIRC, there is like a ground path from the TPS to the MAP/BAP sensor and to the EGR. Jrichker is the one with the master post on this. i would have to break out a manual to figure it out. if you search Jrichker's posts for a code 34 reply, you should get the goods.

good luck.

 

[jrichker]

Code 34 Or 334 - EGR voltage above closed limit - Failed sensor, carbon between EGR pintle valve and seat holding the valve off its seat. Remove the EGR valve and clean it with carbon remover. Prior to re-installing see if you can blow air through the flange side of the EGR by mouth. If it leaks, there is carbon stuck on the pintle valve seat, replace the EGR valve ($85-$95).

If the blow by test passes, and you have replaced the sensor, then you have electrical ground problems. Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1 ohm. Next check the resistance between the black/white wire and the negative battery post. It should be less than 1 ohm.

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.

Let’s put on our Inspector Gadget propeller head beanies and think about how this works:
The EGR sensor is a variable resistor with ground on one leg and Vref (5 volts) on the other. Its’ resistance ranges from 4000 to 5500 Ohms measured between Vref & ground, depending on the sensor. The center connection of the variable resistor is the slider that moves in response to the amount of vacuum applied. The slider has some minimum value of resistance greater than 100 ohms so that the computer always sees a voltage present at its’ input. If the value was 0 ohms, there would be no voltage output. Then the computer would not be able to distinguish between a properly functioning sensor and one that had a broken wire or bad connection. The EGR I have in hand reads 700 Ohms between the slider (EPV) and ground (SIG RTN) at rest with no vacuum applied. The EGR valve or sensor may cause the voltage to be above closed limits due to the manufacturing tolerances that cause the EGR sensor to rest at a higher position than it should.

This will affect idle quality by diluting the intake air charge