apexjeepinjoe Posted December 1, 2012 Share Posted December 1, 2012 I have an 1988 4.0 w/manual transmission. When I start it it seems to idle fine but as it warms up it act as if it gets stuck on high idle. I can not kick it down but if I shut it off and wait when I restart it. It starts the cycle all over again. Any ideas of what to check or what it might be? Throttle position sensor or Idle air control?? Link to comment Share on other sites More sharing options...
Comanche County Posted December 1, 2012 Share Posted December 1, 2012 Mine is doing the same thing right now. At start up it revs to 2.5K-3K rpms. I'm thinking its the TPS. I've got lots of extra renix sensors pulled from JY jeeps, but the one I'm lacking is a manual renix TPS. Link to comment Share on other sites More sharing options...
cruiser54 Posted December 1, 2012 Share Posted December 1, 2012 TPS is on it's way out. Replace it and adjust it using the following: RENIX TPS ADJUSTMENT Before attempting to adjust your TPS 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. IMPORTANT NOTE: With the Key OFF, and using the positive (red) lead of your ohmmeter, 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. MANUAL TRANSMISSION: RENIX manual transmission equipped XJs have only a flat three-wire TPS mounted on the throttle body and it provides data input to the ECU. It has three wires in the connector and they're clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. 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. AUTOMATIC TRANSMISSION: RENIX automatic transmission equipped XJs 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 the manual transmission equipped vehicles, 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. Key ON, measure voltage between "A" positive and "D" ground. 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 AUTOMATIC TRANSMISSION RELATED ISSUES: Check the square four-wire connector side of the TPS. If you have ENGINE ISSUES check the flat three-wire connector side of the TPS. 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. Revised 09-22-2012 Link to comment Share on other sites More sharing options...
Biotex Posted December 1, 2012 Share Posted December 1, 2012 Interesting... I logged on to ask why mine was doing the very same thing. Not always, but intermittently. :MJ 1: Link to comment Share on other sites More sharing options...
apexjeepinjoe Posted December 1, 2012 Author Share Posted December 1, 2012 How much does a new TPS cost? Link to comment Share on other sites More sharing options...
fiatslug87 Posted December 2, 2012 Share Posted December 2, 2012 How much does a new TPS cost? Manual $100 Auto less than $30 Buy the auto Link to comment Share on other sites More sharing options...
cruiser54 Posted December 2, 2012 Share Posted December 2, 2012 Manual $100 Auto less than $30 Buy the auto A good TPS for either manual or auto can be had at Napa for under $50. No need to pay big money for a Manual TPS. Use the Auto one and just don't use the plug for the trans. Link to comment Share on other sites More sharing options...
88whitemanche Posted December 2, 2012 Share Posted December 2, 2012 U guys sure its not the idle speed controller motor...just replaced mine the other day and it was plug and plug with no adjusting worked.wonders now Link to comment Share on other sites More sharing options...
cruiser54 Posted December 2, 2012 Share Posted December 2, 2012 U guys sure its not the idle speed controller motor...just replaced mine the other day and it was plug and plug with no adjusting worked.wonders now Possibly. But, the TPS can be diagnosed quite easily and is a high failure rate item. And, if you have a 2.5 like in your profile, you have an ISC not an IAC. Works completely different than a 4.0.. Link to comment Share on other sites More sharing options...
88whitemanche Posted December 2, 2012 Share Posted December 2, 2012 Wow well I learned something new..... Thanks Link to comment Share on other sites More sharing options...
Mack4194 Posted December 2, 2012 Share Posted December 2, 2012 Check both the TPS and IAC with junk yard ones which you can get for a dollar or two. Then look for vaccum leaks. Get a little can of propane and spray all around your intake exhaust manifold and your fuel injectors. Anywhere you think you can get a vaccum leak. This is how I usually find my vaccum leaks when they show up. With the engine idleing high if you spray accross a vaccum leak you will hear it the RPM's drop down Link to comment Share on other sites More sharing options...
Des88MJ Posted December 2, 2012 Share Posted December 2, 2012 I have that issue randomly, usually I find that a vacuum leak seems to cause it, one of the larger vacuum hoses on my intake swells from oil and loses its seal. Link to comment Share on other sites More sharing options...
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