Coach

When I start my 90 waggy, it idles a bit rough but the rpm is ok. As it warms up the idle smooths out but the rpms go up, normally will stop at 1500 rpm but I have seen it at 1750 rpm. I pulled the IAC, cleaned it (along with the throttle body), also pulled the IAC from my parts rig, does the same thing with either IAC installed. I followed cruiser's instructions on the TPS adjustment, it was pretty close to start with. I also did the ground refresh and sensor circuit ground test (.3 ohms, no fluctuations while wiggling wires). I have just recently (less than 25 miles) replaced: Cap, Rotor, Wires, Plugs, O2 Sensor, fuel filter, water pump, clutch fan, tstat housing and tstat, radiator hoses, flushed, boiled and pressure tested the radiator (temp runs at about 205* even when it's below freezing outside) flushed the cooling system. What should I look at now? I know I need to replace the vacuum harness, no leaks but it is really brittle, also the pcv valve tube is really hokey. TIA!!

Radi

I'd give all the vacuum lines, vacuum operated parts and intake manifold a shot of carb cleaner while it's idling high. If the engine speed changes there's a leak sucking the cleaner in. Sounds like something is opening up as it warms and creating a vacuum leak.
If it's brittle it's quite possibly cracked somewhere.

cruiser54

Yep. Good advice here^^.



Renix Vacuum Harnesses
The vacuum harness that attaches to the front of the valve cover and includes the grommet/fitting, and is called the front harness, is Napa part number BK 715-1367
　

http://www.napaonline.com/Catalog/Result.aspx?Ntt%3d715-1367%26Ntk%3dKeyword%26Nty%3d1%26Dn%3d0%26D%3d715-1367%26Dk%3d1%26Dp%3d3%26N%3d0
　
The vacuum harness that is closest to the air cleaner, EGR etc, and is called the rear harness, is Napa part number BK-715-1366.


http://www.napaonline.com/Catalog/Result.aspx?Ntt%3d715-1366%26Ntk%3dKeyword%26Nty%3d1%26Dn%3d0%26D%3d715-1366%26Dk%3d1%26Dp%3d3%26N%3d0

　

The tube from the rear of the valve cover to the intake manifold is part number 715-1365.


http://www.napaonline.com/Catalog/Result.aspx?Ntt%3d715-1365%26Ntk%3dKeyword%26Nty%3d1%26Dn%3d0%26D%3d715-1365%26Dk%3d1%26Dp%3d3%26N%3d0

　

Revised 09-11-2012

Coach

Thanks for the replies, I had intended on replacing all of that, I was just hoping to wait a bit, guess not. I should have mentioned that this symptom did not exist until after I replaced all the parts, before it would stall occasionally coming to a stop or accelerating from a stop, I'd much rather have the issue I have now.

Coach

I finally got a chance to get back to this, replaced all the vacuum lines, haven't sprayed the new ones yet but it's still doing the same thing, only difference is it idles very smooth, just slowly creeps up to 1500 rpm or so.

cruiser54

TPS MAY be history even though it's adjusted properly. You did check it on the flat 3 wire connector, right?

MUKAK

how would one do that?

cruiser54

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

Nick-B

Hi Coach.
My '90 XJ did the exact same thing when I first bought it. The intake manifold bolts were loose. Put a wrench on those puppies and see what happens.
Best of luck!

Roler

Spray it Coach, it will help you find a possible leak.

Coach

Thanks for all the suggestions!!! I will check each of them out. Cruiser, I have the auto so I think I checked them on the 4 connector. I was a little confused by your write up, thought about checking both but didn't. I will now though. Gotta kick my wife back out of the garage so I can get it in, don't want to work in the snow.

Coach

I remember now, I skipped the manual transmission section since I had an auto, but will check that today!!!!

Coach

ok I checked the voltages again today, it was off a little, made the corrections, no change. I checked the intake bolts, got a 1/8 turn on all of them, still did it. I decided to install my used spare to see if that made a difference and wouldn't you know it both screws snapped off while removing them!!! I'm going to try and get them out, we'll see how that goes. Just a question, the lever on the TPS should be under the lever on the butterfly correct? I think mine was over the top but I'm not sure. Thanks!!

Coach

Ok, with the help of a buddy, I was able to get the broken screws out and retapped the holes, put my spare on and it worked almost perfect,idle only climbed to about 1200. Drove it around, shut it off and restarted it, I was happy. Then went back out to take my kid to practice and it's doing the same thing as before so I guess I'm going to have to buy a new TPS. Another issue is my high coolant temps are back, running 215 or so (by the gage), it was about 26* ambient.

Coach

Ordered new TPS, should be here Monday. Hopefully that will take care of it.