Recommendations for a new IAC.

[KYMJ]

So, I've put 3 on my truck over the past year. Today, it looks like I'll need a fourth. Every time I replace it, the truck runs perfect. The first was a cheapo from e-bay and it lasted about 6 months. The second was a BWD from Advanced, because it was the only one I could find local-lasted about 6 months. I just replaced it under warrenty Saturday morning, truck back to running great. Driving home from work yesterday morning it starts running bad again. So I need to buy a fourth I suppose, so I'm looking for recommendations. Or maybe there is something else that might be causing these to go bad. Thanks for any help or advice.

[Dookie]

I don't have any advice on a good replacement as I don't trust anyones parts anymore. (Had a BWD Tps fail also)

But I disabled mine by unplugging it while its idling and now when it starts it doesn't rev up or get stuck at 2000rpms like the renix are known for. It strated doing it again on my xj after fixing it twice so I said screw the IAT cause it never idled up while cold anyway.

[Zenobian_84]

2.5 or 4.0?

[KYMJ]

4.0. Update, drove to work today and the truck is doing good again, so I guess I have some more digging/diagnosis to do. I'd rather just go buy a new DD'er.

[Dookie]

Can you describe how it's running bad? Most IAC related problems are high or low idle. A lot of the time caused by bad grounds or a bad Tps causing the computer to do dumb $#!&

[cruiser54]

Can you describe how it's running bad? Most IAC related problems are high or low idle. A lot of the time caused by bad grounds or a bad Tps causing the computer to do dumb $#!&

 

Right on and true.

[KYMJ]

Sorry about that, been busy working midnights. The truck was stumbling and idleing badly, but intermittantly. Another update, I checked all my sensors yesterday and replaced the thermostat. I use Fail Safe stats, so it wasn't reaching the proper temp. I also found my tps woefully out of adjustment. I suppose that might have been it, the truck ran great going to work last night and back home this morning(25 miles each way). A few sensors didn't have the proper readings, manifold temp sensor, coolant sensor, so I may replace them. Anyway, I've heard it a million times, don't overlook the simple things, and yes I'm guilty. Big thanks to cruiser54 for his very clear post on tps adjustment procedures.

[cruiser54]

Did you do the sensor ground test as described at the beginning of the TPS adjustment procedure?

 

Have you ever done a complete ground refreshing and connector refreshing?

[KYMJ]

no, I did not, my reasoning was because my readings on the tps was 5 volts as described in the Renix diagnosis chart and I was short on time. Maybe flawed reasoning, and the latter should be done, do you have a link?

[cruiser54]

Here are the TPS instructions wit the sensor ground circuit diagnostics at the beginning under "Important".

 

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 a three-wire TPS mounted on the throttle body. This manual transmission vehicle TPS provides data input to the ECU. The manual transmission TPS 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. Adjust the TPS until you

have achieved this percentage. If you can't achieve the correct output voltage replace the TPS and start over.

 

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—FOR 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. 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 four-wire connector side of the TPS.

If you have ENGINE issues check the 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 05-28-2012

[cruiser54]

Here are the ground refreshing directions. Take no shortcuts. This is very important.

 

Renix Ground Refreshing

 

The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.

 

The components grounding at the dipstick tube stud are:

 

Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.

 

The factory was aware of the issues with this ground point and addressed it by suggesting the following:

 

Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.

 

Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.

 

While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.

 

Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.

 

First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.

Remove the other end of the cable from the rear of the head using a 3’4” socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.

 

A suggestion regarding the braided cable:

I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18” long with a 3/8” lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.

 

A further improvement to the grounding system can be made using a #4 cable, about 10” long with 3/8” terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.

 

 

 

If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.

 

 

Revised 11-28-2011

[KYMJ]

Good stuff. I put new battery cables on the truck when I bought it years ago and I recall the braided ground at the back of the head came out of the connector at one time and I simply re-crimped it. I really intended to replace it, but never did. I will deal with all this when I get a chance. Thanks.

[cruiser54]

Good stuff. I put new battery cables on the truck when I bought it years ago and I recall the braided ground at the back of the head came out of the connector at one time and I simply re-crimped it. I really intended to replace it, but never did. I will deal with all this when I get a chance. Thanks.

Very important to have. Takes less than $20 and an hours time to do the ground refreshing with new cables. It will start more quickly, too.

[Dookie]

Yea I ran my new 4awg battery ground to the dipstick bolt so the ecu harness ground directly to the battery. I still over look simple things. Yesterday I got water in my distributor cap which I previously sealed with silicone to prevent that and left the jeep to run home and grab the meter and spare map sensor.