89 Gt Randomly Idles Funny, Help Please!

Discussion in 'Fox 5.0 Mustang Tech' started by stikystikyricky, Sep 21, 2012.

  1. I have an 89 GT 5.0. Not my daily driver. Lately I've noticed that randomly at stop lights my rpms shoot up to 1500-2500 and just sit there. when i put it in first and start to move the rpms drop. As soon as I hold the clutch in they shoot back up.
    I will let the car sit idle for 5 mins and the rpms will slowly drop back down to 800ish.

    The car doesnt always do this but it does randomly. Usually if ive been driving for 15 mins.

    I gave a good friend of mine that is a mechanic. He says its spitting out code "44"? Not sure what that code is... Regardless he says its doing that because I removed my cats and the sensors are acting up. Earlier this summer I had a hole in the wall shop install my flowmasters. They did completely remove my cats and install flowmasters. The exhaust is dumped, (turned down) right after the flowmasters about half way down the car.

    Do you think my lack of cats is causing this?

    My guess was its the throttle positioning sensor acting up. He disagrees because he isnt getting a code for it.
  2. If the removed the cats, they should have done the rest of the work for free, or even given you some $$$. The platinum or paladium catalyst is worth good money on the scrap and salvage market - $50-$150 depending on the amount of catalyst...

    The code 44 has nothing to do with your idle. Here's the place to go to get help to fix it...
    See the "Surging Idle Checklist” for help with all your idle/stall problems. You can guess at the problem and throw parts at it, or you can use the checklist to help you find the problem quickly and inexpensively. The checklist is right here in the Stangnet 5.0 Tech forum and you don’t have navigate to some other unknown web site. It‘s free and doesn’t cost anything: at last count there were more than 103,000 visits and still climbing

    The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the fixes & updates. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

    Now for the code 44/94 code definitions...

    Codes 44 & 94 - AIR system inoperative - Air Injection. Check vacuum lines for leaks, & cracks. Check for a clogged air crossover tube, where one or both sides of the tube clog with carbon.

    Revised 21 Sep 2012 to correct the description of the process that sets the code and include Thermactor Air System diagram.

    If you have a catalytic converter H pipe, you need to fix these codes. If you don't, then don't worry about them

    Code 44 RH side air not functioning.
    Code 94 LH side air not functioning.

    The TAD solenoid/TAD diverter valve direct smog pump output to either the crossover tube attached to the cylinder heads or to the catalytic converters.

    The O2 sensors are placed before the catalytic converters, so they do not see the extra O2 when the smog pump's output is directed to the converters or the input just before the converter.

    The 44/94 code uses the O2 sensors to detect a shift in the O2 level in the exhaust. The smog pump provides extra air to the exhaust which raises the O2 level in the exhaust when the smog pump output is directed through the crossover tube.

    When there is an absence of increase in the O2 levels when the TAD solenoid/TAD diverter valve directs air through the crossover tube, it detects the lower O2 level and sets the code.

    Failure mode is usually due to a clogged air crossover tube, where one or both sides of the tube clog with carbon. The air crossover tube mounts on the back of the cylinder heads and supplies air to each of the Thermactor air passages cast into the cylinder heads. When the heads do not get the proper air delivery, they set codes 44 & 94, depending on which passage is clogged. It is possible to get both 44 & 94, which would suggest that the air pump or control valves are not working correctly, or the crossover tube is full of carbon or missing.

    Testing the system:
    Note that the engine must be running to do the tests unless stated otherwise. For safety’s sake, do test preparation like loosening clamps, disconnecting hoses and connecting things to a vacuum source with the engine off.

    Disconnect the big hose from smog pump: with the engine running you should feel air output. Reconnect the smog pump hose & apply vacuum to the first vacuum controlled valve: Its purpose is to either dump the pump's output to the atmosphere or pass it to the next valve.

    The next vacuum controlled valve directs the air to either the cylinder heads when the engine is cold or to the catalytic converter when the engine is warm. Disconnect the big hoses from the back side of the vacuum controlled valve and start the engine. Apply vacuum to the valve and see if the airflow changes from one hose to the next.

    The two electrical controlled vacuum valves mounted on the rear of the passenger side wheel well turn the vacuum on & off under computer control. Check to see that both valves have +12 volts on the red wire. Then ground the white/red wire and the first solenoid should open and pass vacuum. Do the same thing to the light green/black wire on the second solenoid and it should open and pass vacuum.

    Remember that the computer does not source power for any actuator or relay, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

    The following computer tests are done with the engine not running.
    The computer provides the ground to complete the circuit to power the solenoid valve that turns the
    vacuum on or off. The computer is located under the passenger side kick panel. Remove the kick panel & the cover over the computer wiring connector pins. Check Pin 38 Solenoid valve #1 that provides vacuum to the first Thermactor control valve for a switch from 12-14 volts to 1 volt or less. Do the same with pin 32 solenoid valve #2 that provides vacuum to the second Thermactor control valve. Turning the ignition to Run with the computer jumpered to self test mode will cause all the actuators to toggle on and off. If after doing this and you see no switching of the voltage on and off, you can start testing the wiring for shorts to ground and broken wiring. An Ohm check to ground with the computer connector disconnected & the solenoid valves disconnected should show open circuit between the pin 32 and ground and again on pin 38 and ground. In like manner, there should be less than 1 ohm between pin 32 and solenoid valve #2 and pin 38 & Solenoid valve #1.

    The following computer tests are done with the engine running.
    If after checking the resistance of the wiring & you are sure that there are no wiring faults, start looking at the solenoid valves. If you disconnect them, you can jumper power & ground to them to verify operation with the engine running. Power & ground supplied should turn on the vacuum flow, remove either one and the vacuum should stop flowing.

    Typical resistance of the solenoid valves is in the range of 20-70 Ohms.

    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)




    If you have a catalytic converter H pipe, you need to fix these codes. If you don't, then don't worry about them
    See http://forums.stangnet.com/attachment.php?attachmentid=50636&d=1180923382 for a very nice drawing of the Thermactor Air System (smog pump) plumbing .