Throttle Postion Sensor

[Mac626]

I've been having trouble with my 94/2.3L/5SP lately. The CEL is on and it runs rough and idles rough. Under acceleration it misses really bad until it gets warm, then it doesn't miss quite so much. Once it's warm if I floor or just depress the pedal slightly, the engine smooths out. Anything in between seems to make the missing and rough running worse. I pulled the codes and got 111 (ok) and the extended ones were 121 and 124.

Does this sound like it might be the kind of behavior caused by a bad throttle position sensor? Or are the TPS error codes more likely just a symptom of another problem? I checked the TPS with a multi-meter and the transistion seems pretty smooth, but you can never be sure about these damned sensors.

[mustbusmc]

I'm no expert, but my truck acted the same way when my O2 sensor was broke. The porcelain on the end next to the wire was broke and causing a short. At Idle and full throttle, the engine ran fine, but it barely ran when I gave gas to go up the road. Just check it to see, it's an idea.

[MT-2500]

Tps sensor would be a good starting.
Check for voltage up to specs.
The only true way to test a tps sensor is with a lab. scope.
MT

[stuzman]

Originally Posted by Mac626

I've been having trouble with my 94/2.3L/5SP lately. The CEL is on and it runs rough and idles rough. Under acceleration it misses really bad until it gets warm, then it doesn't miss quite so much. Once it's warm if I floor or just depress the pedal slightly, the engine smooths out. Anything in between seems to make the missing and rough running worse. I pulled the codes and got 111 (ok) and the extended ones were 121 and 124.

Does this sound like it might be the kind of behavior caused by a bad throttle position sensor? Or are the TPS error codes more likely just a symptom of another problem? I checked the TPS with a multi-meter and the transistion seems pretty smooth, but you can never be sure about these damned sensors.

Your code 124 is saying the PCM is seeing a higher voltage than expected. Did you pull the connector and check the resistance of the sensor? If so, put a voltmeter on the signal ground and wiper (center wire) of the sensor and monitor the voltage. When using the DMM, be sure to use the analog bar graph since it has a faster update time than the digital readout. It's possible that you could miss a bad spot when using the digital readout.

Also, I would look closely at the connector, pins and wiring to the sensor. Usually, the problem is in the TPS circuit and the sensor normally checks out okay. So, check all the other stuff mentioned above.

[Mac626]

Okay - I spent a couple of hours changing out the TPS.

In case you are wondering, you have to remove the throttle body to get at the screws to remove the sensor. It seemed as though this part had been removed before and whoever put it back in used locktite or something on the screws. This resulted in me stripping out the heads of the phillips-head machine screws that held the sensor to the throttle body. I actually had to break the old sensor apart to get it off, because I had to remove enough plastic to get a pair of vise grips on the screw heads. I'm getting used to this sort of thing - it happens every time I work on a car.

The good thing was that it gave me an opportunity to clean out the throttle body (which was filthy). The bad thing was that it did not help my problem. I did note that the engine seems a little smoother once it warms up, but that could be my imagination. It still misses/cuts-out under acceleration.

The O2 sensors are on my list of things to replace, but they are expensive. Does it matter which one I replace first (pre-catconv or post), or should I bite the bullet and replace both at once? Is there any way to test them?

Thanks for the information everyone, I really appreciate it.

[MT-2500]

Unless a 02 sensor is bad why replace it?
If it is missing and cutting out work on the tune up end.
Plugs and wires and coils and fuel supply.
8 plugs or 4 plug system?
Mt

[stuzman]

Originally Posted by Mac626

Okay - I spent a couple of hours changing out the TPS.

In case you are wondering, you have to remove the throttle body to get at the screws to remove the sensor. It seemed as though this part had been removed before and whoever put it back in used locktite or something on the screws. This resulted in me stripping out the heads of the phillips-head machine screws that held the sensor to the throttle body. I actually had to break the old sensor apart to get it off, because I had to remove enough plastic to get a pair of vise grips on the screw heads. I'm getting used to this sort of thing - it happens every time I work on a car.

The good thing was that it gave me an opportunity to clean out the throttle body (which was filthy). The bad thing was that it did not help my problem. I did note that the engine seems a little smoother once it warms up, but that could be my imagination. It still misses/cuts-out under acceleration.

The O2 sensors are on my list of things to replace, but they are expensive. Does it matter which one I replace first (pre-catconv or post), or should I bite the bullet and replace both at once? Is there any way to test them?

Thanks for the information everyone, I really appreciate it.

Did replacing the TPS take care of your codes 121 and 124? I'm curious if this phase is done.

[Mac626]

Originally Posted by MT-2500

Unless a 02 sensor is bad why replace it?
If it is missing and cutting out work on the tune up end.
Plugs and wires and coils and fuel supply.
8 plugs or 4 plug system?
Mt

That's my problem, I don't know how to tell if the sensors are bad or not. Trying to track down what's a bad reading and what's a bad sensor is very frustrating.

It's an 8 plug system. I do plan to replace the plugs and test the plug wires. I tried testing the coils, but either I don't understand the test or I'm doing it wrong.

I have not pulled the codes yet after replacing the sensor. I was rushed after doing the job and just parked it after finding out it didn't help. I'll test it later today.

[stuzman]

Originally Posted by Mac626

That's my problem, I don't know how to tell if the sensors are bad or not. Trying to track down what's a bad reading and what's a bad sensor is very frustrating.

It's an 8 plug system. I do plan to replace the plugs and test the plug wires. I tried testing the coils, but either I don't understand the test or I'm doing it wrong.

I have not pulled the codes yet after replacing the sensor. I was rushed after doing the job and just parked it after finding out it didn't help. I'll test it later today.

Yes, sometimes it's a little frustrating checking sensors, etc. when in doubt. At this point, try checking your codes again, to see if that TPS sensor is out of the way and if other codes pop up. As for your earlier post about checking O2 sensors, you can check them. It's better to take a look at the signal with a scope or a scanner which can do some graphing. Some people will argue that you can check the voltage transistions from rich/lean and lean/rich with a DMM. This is true, but it doesn't tell you anything about the frequency of transistions which is just as important. The maximum period for either transistion should be 100ms. The lower the period, the better; 20ms is typical for a good sensor. If you need any other info about that, let me know, but of course you need some specialized equipment to get a true diagnosis. First, see if your TPS code is out of the way.

You may have already seen this post that I made in the past, but maybe it can take some of the mystery out of checking the TPS. The TPS is nothing more than a variable resistor (potentiometer or pot as it's called in the electronics field). Personally, I like to check it with the voltage applied as that checks the circuit from the PCM and the TPS at the same time.

http://www.automotiveforums.com/vbul...d.php?t=479020

[MT-2500]

Mac like Stuzman says. check that code out.
Always clear code and see if the return after a repair.
On the dual ign system it is a little trickie.
You need to check the spark from coils with engine running.
Put a spark tester on the sparkplug end of the plug wire and look for good hot blue spark.
They are hard on coils for some reason.
The best I remeber it only fires one coil while cranking.
Good luck MT

[Mac626]

I replaced the TPS, the plugs and wires and the improvement was dramatic. It actually ran better than it has since I've owned it. This lasted about 4 days. Now it sputters and coughs and won't get past about 45mph. I checked all the vacuum lines and connections, but nothing seems amiss there. I pulled the codes again and NOW it says 157 and 158 - both related to the MAF. I checked the voltages to the connector for the MAF and they are in the correct ranges. Is there any way to test the MAF itself? My Chiltons book doesn't have any additional information.

[MT-2500]

They are hard to check.
If you have MAF sensor codes try to clean with electrical cleaner and make sure you do not have air leaks on the intake hoses also ood wiring at plugin.
If that fails it is time for another MAF sensor.
Any K&N air filters on it?
MT

[Mac626]

Originally Posted by MT-2500

They are hard to check.
If you have MAF sensor codes try to clean with electrical cleaner and make sure you do not have air leaks on the intake hoses also ood wiring at plugin.
If that fails it is time for another MAF sensor.
Any K&N air filters on it?
MT

Okay - thanks. I'll double check the hose since I did have it off when I changed the plugs. I did put some di-electric silicon on the contacts but it did not help. I'll try the cleaner, too.

I just have a stock air filter.



Mac

[stuzman]

Originally Posted by Mac626

I replaced the TPS, the plugs and wires and the improvement was dramatic. It actually ran better than it has since I've owned it. This lasted about 4 days. Now it sputters and coughs and won't get past about 45mph. I checked all the vacuum lines and connections, but nothing seems amiss there. I pulled the codes again and NOW it says 157 and 158 - both related to the MAF. I checked the voltages to the connector for the MAF and they are in the correct ranges. Is there any way to test the MAF itself? My Chiltons book doesn't have any additional information.

There is a procedure to check the MAF by checking the airflow with a scanner and comparing the airflow at various RPM's. This procedure can also be done with a DMM. However, you say that you've checked the voltages and range being supplied to and from the sensor and this is correct. Observing the voltage being fed back to the PCM at various RPM's would let you know if the MAF sensor is good or bad. In any event, try cleaning the sensor and looking for obvious leaks. If that doesn't do anything, then it sounds like you're in need of a MAF sensor.

[Mac626]

Thanks Stuz - sounds like I have neither the equipment nor the wherewithall to conduct that sort of test.

If cleaning it up and checking for leaks doesn't fix it, I'm replacing the damned thing.