ftpiercecracker1 Posted December 21, 2014 Share Posted December 21, 2014 Sup fellas. I'll cut right to the chase. The truck never seems to have this problem on cold starts. But when it gets warm the idle will randomly drop to nothing and the truck will barely stay running/stall if I let off the gas. If I start it immediately after stalling it will rev to 3000 rpm. Sometimes it will stay there until I shut the truck off again, other times it'll come down on its own in a few seconds. The IAC valve is new and the throttle body has been cleaned. The throttle cable and pedal have been inspected and they are not sticking. Even when its running "good" the idle cannot make up its mind. It will sometimes surge and stick at 1500 to 2000rpm during acceleration. It never idles below a thousand rpm once it is warm. The only time it idles correctly is when the engine is cold. I am leaning strongly toward a faulty coolant temperature sensor, the one in the side of the block. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted December 23, 2014 Author Share Posted December 23, 2014 The truck is now stalling so often it is nearly undriveable. I would like to hear someone else's thoughts before I go out and just start buying sensors. And before someone says check the TPS, how does the TPS cause high idle? Since it only controls how the injectors fire. I have played with the TPS with the truck running and it has almost no effect on the idle. I believe I either have a faulty IAC valve or a faulty coolant temperature sensor. The IAC valve is new and I have visually confirmed that it is functioning (moving in and out) but I have no way of knowing if it is interpreting the incoming signals correctly. Keep in mind this is only an idle problem, I have no issues cruising down the highway at 70. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted December 23, 2014 Share Posted December 23, 2014 I have a low idle and stalling issues. TPS should be thoroughly checked because changing mine mostly fixed my stalling. I think the rest of my problems are CTS but I haven't tested it. If the TPS constantly is the wrong adjustment after you adjust it, then change it. And I recommend not changing it with a Airtex/wells. Horrible replacement. Do you know how to test a CTS? Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted December 23, 2014 Author Share Posted December 23, 2014 I would imagine you would put it in a pot of boiling water and check it the ohm readings. But to be honest if I'm going to go through the trouble to pull that sensor out I might as well replace it with a new one. How did the TPS cause your stalling issue? Link to comment Share on other sites More sharing options...
Knucklehead97 Posted December 23, 2014 Share Posted December 23, 2014 It didnt adjust the A/F ratio quick enough when letting off the gas so it dumped to much for to long and stalled it. My stalling problem was different though. Tried to stall at idle rarely but only fully stalled when letting off the gas. And you can test the CTS just by letting the truck idle till it gets up to temp and then you can disconnect it and check the OHMs. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted December 23, 2014 Share Posted December 23, 2014 But it makes some sense to me that the TPS could cause your stalling by not reading correctly and setting the A/F ratio too high when the system gets warm and gets out of open loop. Link to comment Share on other sites More sharing options...
Rockfrog Posted December 23, 2014 Share Posted December 23, 2014 When my TPS was on its way out I had periods of low idle, retardedly high idle (upwards of 3000rpm) and random dead spots. Turns out the TPS was sticking inside, an new tps had me back to an even idle and normal running. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted December 29, 2014 Author Share Posted December 29, 2014 A small development, during one of the rare moments the truck was idling perfect (850-900rpm) I disconnected the IAC valve. I have done this before and noticed the idle did not change, but I have never left it disconnected to see what would happen after a drive. That is what I did this time. Whenever you disconnect the IAC valve it stays at whatever degree of opening it is at. As I had hoped, with the IAC valve disconnected my idle remained a steady 850 to 900 rpm throughout the entire day. This doesn't really say much about the valve or what might be causing it to malfunction, but I can eliminate the possibility of the throttle cable sticking or the butterfly sticking. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted December 29, 2014 Author Share Posted December 29, 2014 The only question I have is, with the IAC valve disconnected will the computer never switch from open to closed loop or vice versa? Is there any reason why I can't leave it like this for now? Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted January 2, 2015 Author Share Posted January 2, 2015 Going on about a week now with no idle problems. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted March 10, 2015 Author Share Posted March 10, 2015 I hate starting new topics, so i am dragging this back up to the top. The truck has ran darn near perfect the whole time the IAC has been disconnected. The only issue i have experience thus far is the truck idles very low in the morning when the engine is ice cold, but after a few miles down the road its flawless, right around 800-900rpm. Shifting has also become a little more technical. In my experience the IAC seems to prolong the rpms for a very brief moment (.5 - 1s?) giving you a window of opportunity to make a smooth transition into the next gear. Without the IAC doing this, when the butterfly in the TB snaps shut the rpms drop immediately, sometimes making shifting a bit of a challenge. But this is just nit picking. Any way, i finally decided to try connecting the IAC again, just to see what would happen and like i had expected the problem returned immediately. Surging/sticking rpm during acceleration, an idle that would never drop below 1100, and stalling. So i decided to buy yet another IAC, even though the current one is less than a year old. It was a generic unit from Advance ( $55 :eek: ), I swapped it out for the old one and it seemed to work quite well. RPMs would hesitate for the briefest moment between shifts, the idle was right around 1000, and i had no high idle. . . . . . . . . . . . . . . . . . . . for the first day. Que today. Truck started fine, idle was good, but as soon as i pulled out of the drive way and accelerated i could feel it surge ever so slightly and i knew the issue was back. On the way to work (15mi) the idle never went below 1100rpm, it got stuck at 2k once or twice for a few moments, and when i got to work it shot up to 3k and stayed there. I even tried cycling the key without success. The drive home after work went fine though, so :dunno: . Since i now work at a Jeep dealership i figured i would take advantage of my substantial employee discount and cough up the doe to get a genuine Mopar factory replacement IAC ( $84 w/ discount :eek: :eek: $120 w/ out :shake: ) I talked with some techs, with limited success. I asked them what controls the IAC and they said the computer. They said that if the Mopar piece does not solve the problem the issue probably lies in the computer, seeing as how it tells the IAC what to do. The IAC i ordered is meant for a 95 XJ. Even though it bolts up to the TB and the electrical connector is the same, is there any chance the IAC from the newer OBD1/OBD2 systems is incompatible with Renix? People do HO swaps all the time while retaining the original Renix electronics and i have never heard single person mention anything about keeping the Renix IAC. Thanks everybody, FPC Link to comment Share on other sites More sharing options...
cruiser54 Posted March 10, 2015 Share Posted March 10, 2015 Use the correct IAC. TEST your TPS using this: RENIX TPS ADJUSTMENT Before attempting to adjust your TPS, there are two things that need to be done. 1) Be sure the throttle body has been recently cleaned. It's especially important that the edges of the throttle butterfly are free of any carbon build-up. 2) With the Key OFF, and using the positive (red) lead of your ohmmeter, set on the lowest scale, probe the B terminal of the flat 3 wire connector of the TPS. The letters are embossed on the connector itself. Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it parallels the valve cover and also over near the MAP sensor on the firewall. If you see more than 1 ohm of resistance, or fluctuation in your ohms reading, some modifications to the sensor ground harness will be necessary. The harness repair must be performed before proceeding. I can provide an instruction sheet for that if needed. TPS ADJUSTMENT FOR ENGINE ISSUES Both RENIX manual and automatic transmission equipped XJs and MJs have a flat three-wire connector to the TPS which provides data input to the ECU. The three wires in the connector are clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. DO NOT UNPLUG THE CONNECTORS !! Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors. Note the voltage reading--this is your REFERENCE voltage. Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For example: 4.82 volts X .17=.82 volts. Loosen both T-20 Torx screws attaching the TPS to the throttle body and rotate the TPS until you have achieved your desired output voltage. Tighten the screws carefully while watching to see that your output voltage remains where it is supposed to be. If you can't achieve the correct output voltage, replace the TPS and start over. Sometimes, after adjusting your TPS the way outlined above, you may experience a high idle upon starting. If that happens, shut the engine off and reconnect your probes to B and C. Start the engine and while watching your meter, turn the TPS clockwise until the idle drops to normal and then rotate it back counterclockwise to your desired output voltage. TPS ADJUSTMENT FOR AUTOMATIC TRANSMISSION ISSUES RENIX automatic transmission equipped XJs and MJs have a TPS with two connectors. There is a flat three-wire connector, same as the manual transmission vehicles have, and it is tested the same as outlined above—FOR ALL ENGINE MANAGEMENT RELATED ISSUES. However, the automatic TPS also has a square four-wire connector, clearly embossed with the letters A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module. THIS SQUARE FOUR WIRE CONNECTOR IS USED FOR TRANSMISSION/SHIFTING RELATED ISSUES ONLY. First off, DO NOT UNPLUG THE CONNECTORS !! Key ON, measure voltage between "A" positive and "D" ground by back-probing the connector. Note the voltage. This is your REFERENCE voltage. Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage. For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage. If you can't, replace the TPS and start over. So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and the other side feeds the TCU. For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced. The square 4 wire connector is just not used. Revised 12-15-2013 Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted March 11, 2015 Author Share Posted March 11, 2015 Cruiser, I consider your posts to be holy Jeep gospel, but i have never understood why so many people look to the TPS as a cause for high idle. Correct me if i am wrong here. The TPS tells the computer where the butterfly is and in turn triggers the injectors to add more fuel accordingly. But without extra air from the butterfly opening how can a faulty TPS, no matter how bad, cause a high idle?? It would seem the worst it could do would be to cause the engine to run really rich and idle low/rough. All it has the power to do is mislead the ECU into thinking the engine is getting more air when its not. This has always bugged the sh*t out of me because no one has been able to give me a clear answer. Link to comment Share on other sites More sharing options...
Rockfrog Posted March 11, 2015 Share Posted March 11, 2015 Because if the TPS is saying the throttle is at X position, the engine starts to richen up. The O2 sensor relays the rich condition, the IAC may open up some, and the injectors may be dialed back. But the TPS says you need more so the PCM does whatever it can to accommodate your need. Hence a high "idle" is experienced. All the sensors work together not just one task and that's it. You also have to remember the engine has access to way more air than it needs even at idle, it Will pull what it needs. Any vacuum/intake leaks will exacerbate this. Case in point, when I was swapping the GM 2.8 tps, all other sensors/parts were unchanged. Renix TPS, perfect idle no issues. GM TPS with stock Renix wire placement ... Meaning the PCM was seeing WOT ... 3000rpm idle. Swap wires to correct GM orientation ... Perfect idle. The 4.0 runs lean in Stock form, so a little more fuel will mean increased rpm even with the IAC closed (there is still an air passage open, the IAC just increases the openning) At least that is my understanding of it. And yes the taper of the pintle/seat is different between Renix and HO. Link to comment Share on other sites More sharing options...
cruiser54 Posted March 11, 2015 Share Posted March 11, 2015 Cruiser, I consider your posts to be holy Jeep gospel, but i have never understood why so many people look to the TPS as a cause for high idle. Correct me if i am wrong here. The TPS tells the computer where the butterfly is and in turn triggers the injectors to add more fuel accordingly. But without extra air from the butterfly opening how can a faulty TPS, no matter how bad, cause a high idle?? It would seem the worst it could do would be to cause the engine to run really rich and idle low/rough. All it has the power to do is mislead the ECU into thinking the engine is getting more air when its not. This has always bugged the sh*t out of me because no one has been able to give me a clear answer. Very common in the day. Bad TPS tells the ECU that the throttle is open when it isn't. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted March 12, 2015 Author Share Posted March 12, 2015 Because if the TPS is saying the throttle is at X position, the engine starts to richen up. The O2 sensor relays the rich condition, the IAC may open up some, and the injectors may be dialed back. But the TPS says you need more so the PCM does whatever it can to accommodate your need. Hence a high "idle" is experienced. All the sensors work together not just one task and that's it. You also have to remember the engine has access to way more air than it needs even at idle, it Will pull what it needs. How? There is no computer controlled orifice other than the IAC that would allow extra air to enter the engine. Any vacuum/intake leaks will exacerbate this. Case in point, when I was swapping the GM 2.8 tps, all other sensors/parts were unchanged. Renix TPS, perfect idle no issues. GM TPS with stock Renix wire placement ... Meaning the PCM was seeing WOT ... 3000rpm idle. Swap wires to correct GM orientation ... Perfect idle. The 4.0 runs lean in Stock form, so a little more fuel will mean increased rpm even with the IAC closed (there is still an air passage open, the IAC just increases the openning) At least that is my understanding of it. And yes the taper of the pintle/seat is different between Renix and HO. They way i see it is the TPS causes high idle indirectly. I am blaming a faulty IAC when it is in fact merely following orders, so to speak. For the most part everything you have said (Rockfrog) is pretty much what i was getting at, the only bit i missed was where the O2 picks up on the rich condition and tells the IAC to open up a little. Soooo, even though the IAC maybe creating the high idle, it is not the cause. I guess its time to try replacing the TPS. thanks guys, i will give a TPS a shot and report back. FYI it maybe be a week or so before i can get back to yall. Link to comment Share on other sites More sharing options...
cruiser54 Posted March 12, 2015 Share Posted March 12, 2015 Trust me...... Garbage into a computer equals garbage out. Link to comment Share on other sites More sharing options...
HOrnbrod Posted March 12, 2015 Share Posted March 12, 2015 Trust me...... Garbage into a computer equals garbage out. Better said: Garbage into a RENIX junction box equals garbage out since it's not a computer. Link to comment Share on other sites More sharing options...
cruiser54 Posted March 12, 2015 Share Posted March 12, 2015 Nah. It's pretty forgiving. If it wasn't, we never woulda been able to do what we did/do with it. Link to comment Share on other sites More sharing options...
HOrnbrod Posted March 12, 2015 Share Posted March 12, 2015 Have you been drinking? Link to comment Share on other sites More sharing options...
cruiser54 Posted March 12, 2015 Share Posted March 12, 2015 Of course!! Link to comment Share on other sites More sharing options...
HOrnbrod Posted March 12, 2015 Share Posted March 12, 2015 Me too! :cheers: Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted March 17, 2015 Author Share Posted March 17, 2015 Well, there is not much more to say other than when your right your right. I bought the best quality TPS i could find, (NAPA brand), installed/adjusted per your (Cruiser) guidelines and she is as right as rain. No high idle, no stalling, nada. She runs and idles smooth as butter. Although i still can't stand not knowing why the TPS caused the problems. In the instructions it says to turn your key to the 'ON' position when setting up the TPS. I got nothing from any of the wires with the key in the 'ON' position, i had to have the key in the 'RUN' position before any juice got to the TPS. I was able to adjust everything all the same, obviously, this was just a small detail that caught my attention. Also the resistance to battery negative was .8 ohms. Link to comment Share on other sites More sharing options...
cruiser54 Posted March 17, 2015 Share Posted March 17, 2015 To me, On and Run are one and the same. Resistance to battery from where? Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted March 18, 2015 Author Share Posted March 18, 2015 B terminal Link to comment Share on other sites More sharing options...
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