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The RenX Files: High idle problems

Great old threads never die, LOL. Glad it has helped. Interesting to hear of the heat effect too!!!! Most interesting

Got any pictures of the dissected TPS?

I had a brand new IAC that was bad right out of the box 2 weeks ago.
 
I used to change that damn IAC every six months or so on my 90. That was the one thing about that jeep that made me insane. Now I 've got a 96.
 
Hi all!

I've had the intermittent high idle issue for quite a while now, and frankly i've just been ignoring it. Until recently it was usually fine, and would only act up sometimes. Well recently its started to be a more often than not problem, and of course it would because my smog check has just come due! Of all the rotten luck!

I tried a whole list of things from this thread including replacing/upgrading all the grounds and testing all the sensors. No change. I reset the TPS to .815VDC. No change. I replaced the Idle air control motor. No change.

So I started looking elsewhere, and I just have a quick question.

In the photo below, is there supposed to be any vacuum coming through the little hole at the bottom of the photo? When I block this little hole, the idle drops down to ~800rpm or so and if I put my finger over the hole for the IAC I can feel little pulses as it adjusts to let a little more or less air in. I turned the torx screw on the side of the TB to shut off the litttle passage, but it's nagging me because it seems a screw would cause a constant high idle, not an intermittent one... I kept track of how many turns i shut it in case i have to put it back.

4862386412_e1cb1e3c3f.jpg
 
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Check your EGR valve for sticking.
 
Like sticking shut or not opening? when I rev the engine I can see the little pin between the vacuum diaphragm and the egr move, and if I manually pull back that pin the engine bogs down and runs like poo. I don't think it's stuck... *shrug* I'll try to post a list of everything that I have already done to it tomorrow.
 
Sounds like you have a vacuum leak now. I would look everywhere there is a vacuum line for even the smallest leak!!! Once all the leaks are fixed then you can deal with calibration. I would suggest pulling and cleaning the inside of the throttle body with carb cleaner, then reinstall with a NEW gasket.

I actually had a brand new IAC fro Autozone that was defective right out of the box 6 weeks ago!!!! So look into that possibility too.

Once you have all the vacuum leaks fixed (even the valve cover gasket needs to be air tight), then you calibrate the idle air screw (torx) on the throttle body side that you mentioned. It does not take much trash inside the throttle body. carbon build up, to cause IAC travel problems that make a fast idle.
 
Guy had an intermittent 2500 RPM high idle, it was the transducer valve in the EGR system.

TEST your EGR system, info from 90 FSM:

Warm the engine to normal operating temperature.

Operate engine at idle speed.

Check vacuum at solenoid vacuum source.

Disconnect the hose and attach a vacuum gauge to it.

Vacuum should be at 17 inches.

If vacuum is low, check the line for kinks, twists, or a loose connection at vacuum connector on intake manifold.

If vacuum is ok, remove gauge , reconnect the line and proceed to next step.

Check vacuum at solenoid output port.

Disconnect the line and attach a vacuum gauge to output port. Vacuum reading should be 0 at this side of solenoid.

If vacuum reading is 0, leave the gauge connected and proceed to the next step. However, if vacuum is present check solenoid/ECU operation with the DRB-ii tester.

Disconnect electrical connector at solenoid and note vacuum at output port. Vacuum should now be present at output port.

If vacuum is present, proceed to EGR valve test. However, if vacuum is not present, replace the solenoid. Test the EGR valve as follows:

Leave solenoid electrical connector disconnected. Note engine idle.

The engine should idle roughly or stall. If this occurs the valve is ok. If the idle does not change, proceed to next step.

Disconnect hose from the EGR valve and connect a hand vacuum pump to EGR nipple.

Apply a minimum of 12" of vacuum to the valve and note engine idle. If engine now idles rough inspect the vacuum line between the EGR valve and the solenoid.

If the idle did not change, remove the EGR valve and inspect the valve and the exhaust passage in the manifold for blockage, repair as necessary. If no blockage is present replace the EGR valve.

TRANSDUCER VALVE:

Disconnect the transducer vacuum lines and the back-pressure line (bottom). Remove the transducer. Plug the transducer output port. Apply 1-2 pounds air pressure to the back-pressure port. Apply a minimum of 12 inches of vacuum to the input port. Replace the transducer if it will not hold vacuum.
 
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gradon said:
Renault + Bendix = Renix
Click to expand...

I kinda thought so. Just checking.

Well when I started the jeep up this morning it idled fine, 850rpm or so from a cold start. By the time I got to work which takes about 30min of combo freeway/surface streets the idle was back up at 1100 and wouldn't go down. Below is a list of everything that I have tried so far.

- Replace/Upgrade all ground wires. Neg term to block is now 2AWG fine strand. Replaced the block to firewall strap with 4AWG, and added a 4AWG wire from the neg bat terminal right to the fender bolts. I removed sensor ground wires from block near the dipstick. They were kinda corroded and soaked in oil, so I cut back a few inches until I found clean copper and crimped/soldered new ring terminals to each of the 4 wires. These have been re-routed to a terminal block on the firewall (away from my leaking valve cover) where they connect with a 10awg wire that connects directly to the neg battery term. Resistance from all sensor grounds now reads 0.00 Ohms. (Note: Before the replacement the resistance was only 0.01 Ohms, but after reading through here I knew i'd have a problem sooner or later.)

- Check TPS voltages. Supply voltage from the ECU reads 5.04VDC to ground. Signal back to he ECU was adjusted to read 0.814VDC. These were both measured with the ignition on, engine off.

- Coolant temp sensor: I measured the resistance across the sensor with a hot engine (~190 degrees) and got 467 Ohms. This seems to be in-spec. This was the sensor toward the bottom of the block near the knock sensor, not the one up in the head that operates the gauge.

-Manifold air temp sensor: I measured the resistance across the sensor with a hot engine (~190 degrees) and got 527 Ohms. This seems to be in-spec.

- MAP sensor: With the ignition on, engine off, the supply reads 5.04VDC and the signal back to the ecu is 4.62vdc. With the engine running at idle (1100rpm) the signal was @ 1.226VDC

- O2 Sensor: was replaced last week with no effect. I haven't a clue how to test these so I just replace them...

- IAC motor: Another component I have no real way of testing... So I replaced it. It seems to be working, as I can feel changes in vacuum when I put my finger over the hole in the throttle body that feeds it. I can't tell if it's shutting all the way though. Is there any way to test for that?

- Tighten all manifold bolts: They weren't loose, but i tightened them some more just in case

-Check for leaks: I sprayed carb cleaner on everything that was hooked to vacuum, and some stuff that wasn't! to make sue it wasn't a leak inside the cab I even disconnected and plugged the lines that feed the heater controls and the evap canister at the manifold.

- I also recently replaced my spark plugs, cap, rotor, and ignition wires. Strangely the problem seems more consistent after this, but I can't draw a connection as to why those components would have any effect. something in the distributor perhaps?

Lastly, the jeep will sometimes idle at 3000+rpm and the only way to stop it is to turn the ignition off. When it restarts the problem may or may not be gone. Driving it in this condition will let me get up to about 45MPH without touching the gas. This problem is far less frequent, but I suspect it is related. I was able to trigger it actually while testing last night by pulling the vacuum line off the map sensor and then starting the jeep. The engine ran like crap until I put the vacuum line back and then it reved up to 300RPM. Turning it off and starting it again made that go away. I think I may try a new MAP sensor tonight even though the current one tested "good." I feel like i'm just throwing parts at it now though.
 
What year is yours?

Next time it is idling high, let it run and test all the sensor voltages live!!!!! Carry your meter with you, pull over to a parking lot when it acts up. If you have an intermitently bad part it might show up then!!! You have be sneaky, and sneak up on these morphodite gremlins!

Is the TPS NEW!!!!!

Does it have C-101 bulkhead connector, with goofy contacts?
 
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As I posted above, another user was hitting 2500 RPMs when his idle was wonky--it was his transducer valve.
 
I'll check the transducer when i get home... all my vacuum tools are there. Thanks for the suggestions, i'm pulling my hair out on this one.

@Ecomike its an '89. well, most of it is anyway!

... and to top it all off, my AX15 is on its deathbed. There's all kinds of scary noises coming from under there.
 
xytrix01 said:
I'll check the transducer when i get home... all my vacuum tools are there. Thanks for the suggestions, i'm pulling my hair out on this one.

@Ecomike its an '89. well, most of it is anyway!

... and to top it all off, my AX15 is on its deathbed. There's all kinds of scary noises coming from under there.
Click to expand...

Ouch!
 
Ok, so as per joe_peters suggestion, I went through the test procedures for the egr system.

Results:
Warm the engine to normal operating temperature. Done

Operate engine at idle speed. Done

Check vacuum at solenoid vacuum source.

Disconnect the hose and attach a vacuum gauge to it.

Vacuum should be at 17 inches. Yep, jumped around a little but it was 17 to 18

If vacuum is low, check the line for kinks, twists, or a loose connection at vacuum connector on intake manifold.

If vacuum is ok, remove gauge , reconnect the line and proceed to next step. Done

Check vacuum at solenoid output port.

Disconnect the line and attach a vacuum gauge to output port. Vacuum reading should be 0 at this side of solenoid. Yep, nothing

If vacuum reading is 0, leave the gauge connected and proceed to the next step. However, if vacuum is present check solenoid/ECU operation with the DRB-ii tester.

Disconnect electrical connector at solenoid and note vacuum at output port. Vacuum should now be present at output port. Full vacuum present

If vacuum is present, proceed to EGR valve test. However, if vacuum is not present, replace the solenoid. Test the EGR valve as follows:

Leave solenoid electrical connector disconnected. Note engine idle.

The engine should idle roughly or stall. If this occurs the valve is ok. If the idle does not change, proceed to next step. Engine dies when connection is pulled

Disconnect hose from the EGR valve and connect a hand vacuum pump to EGR nipple.

Apply a minimum of 12" of vacuum to the valve and note engine idle. If engine now idles rough inspect the vacuum line between the EGR valve and the solenoid. Done, Jeep dies

If the idle did not change, remove the EGR valve and inspect the valve and the exhaust passage in the manifold for blockage, repair as necessary. If no blockage is present replace the EGR valve.

TRANSDUCER VALVE:

Disconnect the transducer vacuum lines and the back-pressure line (bottom). Remove the transducer. Plug the transducer output port. Apply 1-2 pounds air pressure to the back-pressure port. Apply a minimum of 12 inches of vacuum to the input port. Replace the transducer if it will not hold vacuum. Done

My transducer valve tested bad, it would not hold vacuum. Lucky me I bough one at the wreckers! This one tests good out of the car, BUT when installed and the test is repeated, no vacuum gets to the EGR during the step where the electrical is disconnected to allow vacuum through the solenoid. If I remove the back pressure line from the bottom and apply pressure by blowing gently into it, it opens up and lets the vacuum open the EGR and kill the engine. i'm thinking that perhaps the back pressure port is partly clogged? I can feel a little bit of exhaust leaving it, but it isn't much.
 
Well, even with the "new" transducer and a brand new MAP sensor, this mornings report is the same. Stat it up, idle is right where I want it, about 800rpm. By the time I get to work and the motor is all warmed up, it refuses to drop below 1100rpm. i am going to pull the EGR and see if I can clean the back pressure tube, but I am really boggled by this.
 
Did you test the sensor voltages, and TPS voltages when it got 1100 rpm, like I suggested?

Sounds like a tiny possible intake/exhaust manifold gasket leak when it warms up. The intake and exhaust are aluminum and iron, and expand at different rates. On top of that the 4.0 uses one bolt with a special washer that overlaps the iron and aluminum in a number of positions (about half the bolts IIRC), and at best, it is a poor design. Just the slightest warpage or bolt that is not properly torqued (threads could be dirty/rusted give a false torque indication??). Could also be a spot burned or carbon covered spot on the gasket where it was once loose, and later retightened, but is not flat-flush seal!

If you are that close to solving the problem, only 1100 rpm, try adjusting the torx screw to idle hot at 800, then let the IAC/Renix system readjust. It may 3-4 start, run, get hot, shot down run cycles, for the Renix computer to clear its memory of old sensor data too!!!!!!! In other words, the old data in the computer can do weird stuff to rpms, until it is written over with new historical data.
 
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@Ecomike I haven't gotten a chance to do the running sensor tests yet because I had to get my butt to work and I was late... Now as for the torx idle screw... I've cranked it in all the way, closing the port. This brought the idle down at the time that I did it, but it seems to have compensated for it and is back up at the high idle. I figure it has to be either a vac leak somewhere or a sensor that is telling the computer to open up the idle air motor for some reason... I wonder if my new O2 sensor is faulty... any way to test it without expensive equipment?
 
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