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Followup To
Question -
99 Hyundia Tiburon with 2.0L,2 days ago had to change ECM, ECM relay and 20amp fuse link (all for ecm).Vechile now ran, but extremely bad and showed too many codes.Changed spark plugs and both coils fire.. Problem is after driving idle fluctuates up and down, most times to a stall. NO CODES, No check engine light.Could it be throttle position sensor? If so what should it read?
Answer -
The throttle position sensor is a possibility, but you might wish to check the camshaft timing first. The condition you describe frequently occurs if the camshaft timing is off a tooth. The throttle position sensor voltage at idle should typically be around 500mV.
I'm more curious, however, as to why you needed to replace a fuse, the ECM relay, *and* the ECM. What were the trouble codes? What was the cause of all of these components failing? ANSWER : The car would not start had all plugs firing,but no fuel in manifold, checked fuel pump no power,ran test power wire to pump and fuel was in the fuel manifold,but no injectors opened. tested both cam and crank sensors(they were O.K. The reason the ecm 20 amp "fuse link" and the ecm relay were changed is that the link was blown and would take another fuse without blowing. I got the car to start with a new ecm relay and a new fuse(removed relay cover and it was burned)but the car ran extremely bad. Check engine light came on. Plugged in an Actron CP9135 (OBD 2)reader the car ran fine.The codes that came up were 101(Map sensor or baro or any air intake problem),115 (engine coolant temp),121(throttle position sensor)450(fuel tank pressure)and some others. Because the car ran O.K. with the Autoscanner on. So then I replaced the ECM computer...Now the problem is my question (car will not idle)(Also I don't think it is off a tooth on timing, the car seems to accelarate good, but this is not my car but my niece's,so this is not your regular driver of this car. (99098 miles)..This evening (2days after the replacement components) the check engie light did come back on and the code is 121( pedal position sensor) ?Is that the same as throttle position sensor located on the side of the intake. I did the best I could on holding idle at 800rpm and the voltage from the throttle sensor( set at milivolt was 1)(too much for that range setting moved the range setting on the meter to 2 volt and it reads .25 volt.
AnswerThe fact that the fuse blew in the first place suggests that there may have been a significant electrical issue. Was one of your codes for an abnormal system voltage? Has your air bag warning lamp come on?
Certainly a TPS issue can cause an abnormal idle condition, and the P0121 code (throttle position sensor) is almost always caused by the throttle position sensor itself. But because of what you've told me so far, I'm reluctant to suggest that as a probable solution to this problem.
I have some significant concern that the alternator may be defective and be overcharging, at least intermittently. If you had a code for the system voltage being too high in either the ECM or the air bag system, I recommend replacing the alternator before you even start the car again. An overcharging alternator has the potential to destroy just about every electrical component in the vehicle.
Next, check the reference voltage to the TPS. Power to ground should be 5V. I looked up the actual value in the shop manual for the TPS signal, and it should be 100 to 875mV with throttle closed. Don't try to keep the engine idling when checking this, because throttle may no longer be closed when you do this. Just check it with the engine off and key on.
Next, check for vacuum leaks, especially in the PCV hose. This can cause an erroneous TPS code, especially if you don't have an air flow sensor.
