High Idle/CA Smog - 1989 Renix Federal Model

[BulletMaker]

So I'm missing out on all the nice weather up in WA right now trying to get the wife's jeep up and running to pass smog so we can get on with the move (reg is currently out).

I havn't monkeyed with it much in a few months, but I need to get this thing up and running so I can take my truck back.

Anyways, there are two main issues, first of which is a high idle on startup, not the creep-up that there are tons of write-ups for, but you turn it on and it's spinning the engine at ~2000RPM. Didn't do this when we first bought it last year, but it's now a major issue.

Corrective action taken:

I went through and methodically replaced all vacuum lines, this one has an NP231, however since 4wd isn't needed ATM I disconnected the lines for the axle.

Seafoam'ed the intake and throttle body. More than a few write-ups suggested this as an issue, so I went through and cleaned every part I could get to with carb cleaner and a rag, then I turned it on and blew seafoam through the whole thing.

Engine/Chassis grounds - Many suggested this is also a common culprit, while the grounds were f-ed up, I replaced the whole mess, now has nice new marine terminals with a grounding connection to the main point (next to the dip-stick bracket. All connections cleaned with wire brush, coated in preservative, and new 4ga cables connected from battery to engine, and to chassis

New O2 Sensor - The one on there was pretty baked, put a new one in to help it pass smog.

Cleaned EGR system - Removed valve, filled full of crud cutter, jagged it out with wire brushes, turned it over to blow everything out. EGR seems to be working normally.

For giggles, I double checked the vacuum system, near as I can tell no leaks.

So, my main suspicions are that it's probably a bad IAC/TPS.

However, the NOx emissions from the first test were in the <800 range (almost passing). Now that this high idle issue has come up, it's now testing with NOx at about 1700.

Suggestions? Dispersions? Questions?

 

[cruiser54]

Sounds like your TPS is toast. Replace it and adjust it per the instructions below, on the "engine" side.


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

 

[Ecomike]

Also test the MAT (IAT) air intake temp sensor. Might try cleaning it too.

Try disconnecting the TPS with engine running, does the idle drop? If yes, it is NOT the IAC and not a vacuum leak!!!!!

 

[BulletMaker]

That's some solid info there EM, because yes, I tried this and idle did not drop. Which made me think it might be the issue.

I have a spare IAT, I'll try dropping that in and see if it helps. I did clean the IAT a few weeks ago, but didn't seem to make anything better. I need to run over to the junk yard today and see if I can find an upgraded break booster. My thought was the booster could be a source of a vacuum leak (all the rest of the tubes are brand new).