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Old 11-12-2012, 06:21 AM   #1
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Throttle body

I have a 91 jeep YJ and it has a rough idle. I took it to a mechanic and he put it on a diagnostics test and came up with nothing. My question is could my throttle body sensor cause the jeep to run rich? I'm running out of options.

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Old 11-12-2012, 04:31 PM   #2
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What have you replaced so far? By Throttle Body Sensor I assume you mean the Throttle Position Sensor? It can cause the engine to run rich if it's not giving a high enough input / output, the EEC wont receive a signal from the TPS, so it adds more fuel to the mixture to keep the engine running, preventing the engine from stalling even though it really doesn't need to, increasing the fuel in the fuel/air ratio (rich). Do you have an engine light present at idle? What is your idle RPM currently? There is no way to check a TPS unless you OHM it out, it's one of those things that works / doesn't work / partially works. Post a detailed list of everything you have done personally, and the results from the diagnostics test from the mechanic (CO, CO2, O2 levels, etc), and we'll try to come up with a reasonable troubleshooting procedure

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Old 11-12-2012, 05:45 PM   #3
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Ok I've used seafoam to clean the throttle body I've changed the o2 sensor and yes I mean the throttle body positioner sensor. The mechanic never charged me for dianostics he didn't even give me a sheet. When the jeep is on idle it kind of feels like it has shiver kind of like it wants to stall.
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Old 11-12-2012, 05:46 PM   #4
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Oh and there is no check engine light on. The code reader doesn't give any codes.
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Old 11-12-2012, 11:19 PM   #5
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Ok man thanks for the info. Based on what your symptoms are I think you have one of the following problems. If your Jeep is running rough -and- rich, it can be 1: air flow related or 2: electrically related. I'll try to give you what I think is a reasonable procedure to troubleshoot and try to eliminate systems/sensors one by one. I want you to try these AIR related faults first, then come back and report what you find in detail. We'll try electric afterwards if your problem doesn't improve but try these first:

AIR: (Your Jeep will run rich when the air ratio is decreased, particularly at idle when the EEC has to apply a set-minimum amount of fuel to keep the engine motoring)

- Take off the air tube intake at the throttle body, so you can see the butterfly valve. Turn the Jeep on, if your idle increases or the roughness decreases, you have a restriction in the air intake system, possibly a blockage in the filter or foreign debris disrupting/diverting the air-flow. (please be careful not to let anything get ingested into the TB, the suction will be immense since the surface area is much larger than the diameter of the intake tube)

- If problem continues, take off the negative and positive battery terminals and let the Jeep sit overnight. This will deplete all the capacitors in the EEC, resetting the computer back to factory settings. The EEC will have to "re-learn" the engine and it's sensors for the first 50 start-ups. Try this step b/c you bought a new O2 sensor and perhaps the EEC doesn't recognize it yet. Reset the computer and see of the symptoms change. Reconnect and start it up again.

- If the problem remains, take off the Idle Air Controller. Keep the IAC connected electrically at the connector, but take it off of the throttle body and hold it in your hand. Get a buddy to "key-on" the engine, (not turn on or crank, but just "key-on" one notch on the steering column). When you "key-on" the EEC commands the IAC to retract the plunger. The plunger should physically move when you do this, not less then 1/4" aprox. The plunger acts as a variable air controller, when idling the plunger should be retracted allowing the most "idle-air" past the butterfly valve. As you accelerate past idle, the plunger will extend and the butterfly valve takes control of the airflow. If if the plunger is stuck in the extended position or "slow-to-change", it will deprive the engine of air, then the EEC will add more fuel to keep it running. Replace the IAC if it hesitates or doesn't move at all when you "key-on"

-Adjust the Idle set screw 1 complete revolution "up". The set screw is located just below the throttle cable spring bracket. The bracket actually hits the screw, (but it won't if it's down completely). I believe it will take an 1/8" allen key to adjust it, but it could be smaller. Turn it up 360' and see if the roughness decreases. If it is already up, count how many threads you can see or the total length and post back what you find. Don't change it if it's up already, but you can if you want a temporary fix of the roughness.

- At this point I would have said clean the system out, but since you Sea-Foamed it you should be good.

- If the problem still exists "borrow" a new Throttle Position Sensor from Autozone or Advanced Auto, you don't actually have to install it on the TB to see if it's working, just disconnect the old TPS and connect the electrical connector to the new TPS and hold it in your hand. They are spring loaded and should be at neutral 0-degrees. The TPS will relay that the butterfly valve is at 0' (180') and the EEC will add the determined amount of fuel for optimum engine idle. Like I said before, if the TPS is sending out incorrect angles/positions of the butterfly valve, the EEC will by default add more fuel to prevent the engine from stalling, since it doesn't really know the actually position of the B-valve.

- If the problem continues, "borrow" a new Manifold Air Pressure sensor from the auto store. Install, and see if anything changes. The MAP relays info back to the EEC just like the TPS.

-If you still have the same roughness, reset the EEC again. By this point you should have a new O2, IAC, TPS, and MAP. Let the EEC re-learn the new sensors.

Hope this points you in the right direction, take your time and post back what you find, good luck man (P.S. make sure you are able to return your "borrowed" sensor from the parts store before you buy parts you may/may-not need, don't get stuck with something you don't want. I know my Advanced Auto Parts is more lenient where as my Autozone makes a big stink about installing sensors and returning them, just make a big enough stink yourself and they'll give you the $ back lol)
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Old 11-13-2012, 04:08 AM   #6
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Thanks man ill try this out for sure. I don't think the autozone guys will let me borrow anything but I'll give it a shot.
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Old 11-13-2012, 10:09 AM   #7
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By "borrow" I mean "buy it then return it" lol
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Old 11-13-2012, 10:26 AM   #8
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Oh ok I got ya. I thought u meant they would lend it to ya to try
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Old 11-19-2012, 04:05 PM   #9
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Ok I've taken the throttle body off and I gave it a good cleaning. I took the sensor that is on the throttle body off and cleaned that as well. The jeep is idling better until it gets warmed up then it starts to act up. It starts idling rough abit and it also starts to hesitate. Any suggestions?
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Old 11-20-2012, 06:01 PM   #10
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Also it still seems like I'm burning through a lot of fuel.
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Old 11-23-2012, 03:32 PM   #11
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Originally Posted by Jdusome View Post
Any suggestions?
Keep following the troubleshooting procedure I gave you above, you cleaned components and if the problem still remains you have to start removing and replacing components.

Which sensor did you take off the TB and clean? There are two of them on the TB. You can't clean the TPS it's electrically controlled, it works or it doesn't, it doesn't sit in the airstream to get dirty in the first place unlike the IAC. The IAC is cleanable, it has a moveable plunger that is exposed to the airstream and will gunk up. The oil vapors coming from the valve cover line are aft of the air filter, so it gets very dirty over time.
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Old 11-23-2012, 07:20 PM   #12
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I took the iac off and cleaned it. Then I took the throttle body off and I cleaned that inside and out. Since I've done that the jeep has been backfiring. The rough idle got better it only does it when the motor is warm.
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Old 11-23-2012, 07:24 PM   #13
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I forgot I changed the o2 sensor. I didn't do the test on the iac to see if the plunger worked. I also took the battery cable off for 24 hours
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Old 11-24-2012, 12:06 AM   #14
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Quote:
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I took the iac off and cleaned it. Then I took the throttle body off and I cleaned that inside and out. Since I've done that the jeep has been backfiring. The rough idle got better it only does it when the motor is warm.
Good good I'm glad to hear it's getting better, keep at it and keep us posted on the progress
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Old 11-24-2012, 06:26 PM   #15
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Ok I've got a new symptom to my rough idle. I just went outside when it was alittle chilly out. I started the jeep up and it was running really rough. I drove it anyways. It had a lost of power a lot more backfiring and it smelt like something was burning under the hood
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Old 10-04-2013, 09:14 PM   #16
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I know I'm a little late to the party, but have you checked the CCV to Manifold and CCV to Air Cleaner tube assemblies for cracks, leaks, blocks, or loose connections?
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Old 10-04-2013, 09:39 PM   #17
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Quote:
Originally Posted by Jdusome View Post
........... I took it to a mechanic and he put it on a diagnostics test and came up with nothing.........
That is all I needed to see, Take it somewhere else!

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Originally Posted by DoctorVegas View Post
I know I'm a little late to the party, but have you checked the CCV to Manifold and CCV to Air Cleaner tube assemblies for cracks, leaks, blocks, or loose connections?
CCV is for a carb, he has EFI, hence the IAC and Throttle body...

EDIT: wait, you mean the PCV Breather? (Fresh ait into the Crankcase? that does not go to the manifold, the PCV Vacuum line goes Valve cover to vacuum, but thats not the CCV side...)

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