stalling

I looked on the search & found nothing to relate to this problem I have. My truck dies pretty often at red lights, stop signs, and sometimes while turning and slowing down. I have no bad vac. leaks, & everything checks out fine, except this weird thing w/ the throttle. In an effort to replicate the stalling while idling in my garage, I jammed the throttle linkage down (accelerate), & let it contact the throttle stop again. It stumbled a bit but never died. the linkage is a bit sticky, & I can relax the linkage slowly & it will hang up w/ about 1/8 inch of space between the throttle stop. If I jam it again from this position (1'8 inch open) & then force it shut it will die completely.It will not restart , even w/ throttle input. If I get out of the truck again & set the throttle to the same 1/8 inch open, it'll restart! I repeated this scenario several times. My wife will kill me if she has to drive like this tomorrow, please help!

I'm sorry, a little more explanation is in order. It's an '87 auto 4.0. Starting from scratch w/ the throttle stop contacted it runs OK, and will accept a rev & then back to the throttle stop, If I move the throttle slightly off the stop, rev it once, and then return it to the same point (slightly off the stop), the same thing happens. If I then push it against the throttle stop it will die. This makes no sense at all to an old-timer like me.

My stalling issues stopped after I disconnected the EGR valve. Have you cleaned your throttle body and Idle Air Control (IAC) ??? Jamming IAC might also be the reason to your problem...

There is a gizmo on the side of the throttle body called an IAC, idle air controler. There is a seperate (smaller opening) in the top of the throttle body, that bypasses the normal opening that works with the throttle. The piston for the IAC, gets gummed up and siezes. You can look down the smaller opening and watch the piston work (go in and out) with the motor running and lightly working the throttle. If the piston doesn´t move, this may be your problem. Check the spring on your throttle body.
If your XJ is a pre 91, it has an EGR valve, if the EGR valve sticks open, it will cause stalling. A quick test is to plug the vacuum line for the EGR. Some models have a modulator (called a transducer) in the vacuum line before the EGR, plug the line before the modulator, just in case the modulator is loosing vacuum.
Just guessing, but the ECU (computer) tries to keep a standard idle RPM and (at least on mine) makes constant adjustments and learns. If the throttle is an iffy thing (closing all the way), could be causing problems in the ECU engine control module.
After you fix the sticky throttle (broken spring) and makes sure the IAC piston is moving. If your XJ is a post 91, you may want to unhook the battery cable for a quarter of an hour or so and then hook it back up again. This has helped me with gremlins in the past. Disconnecting the power doesn´t (isn´t supposed to) help much with a pre 91.
Just a last tip, if you lub the throttle cable use a dry lub, graphit, teflon or silicon. Gease and/or oil will get thick when it gets cold and cause sticking. You could try adding a spring to the throttle arm.
On the early XJ´s the insides of the throttle body are often covered in old oil, from the crankcase ventilation system. Periodic cleaning is necessary, avoid wetting any of the sensors with solvent. Solvent on the sesnors has caused many problems, for many people.

I pluged the EGR line, still stalls. I plugged the vac line at the input of the transducer (I think, small little thing mounted on the drvr side fender, out goes to a vac. junction then to the EGR. It had definit vacuum at the transducer input. COuld this have something to do w/ this TPS you guys are all talking about? I have a 3 flat & a 4 square connector. I will try

I also disconnected all 3 electrical connectors at the throttle body, 2 for the tps & 1 for something I don't know. It changed nothing.

The other plug (not the TPS) is the idle air controller. Sounds like it´s jammed. When you disconnected it the idle should have changed (not always, but mostly).
The IAC is pretty easy to remove, with a small torx tip socket. Just don´t try to move the piston any or it may fall out and watch the gasket.
You may want to squirt a little penetrating oil down the IAC air feed opening as a possible quick fix, but my experience tells me it´s pretty gunked up, on the piston and seat. I usually clean the seat with a smalls stick and the piston with my finger nail, then add just a drop of light oil around the edges of the piston. I avoid using solvent sprays, which have caused me some grief in the past.

I have further isolated the stalling. It will occur whenever the throttle is off idle, accelerated, then jammed shut against the stop. This TPS thing seems troubley, & I saw a plunger that moves w/ the throttle valve (can I carburate this thing?). If I depress the plunger on the tps i CANNOT MAKE IT DIE. With the plunger contacting the thingy on the throttle valve it will move in concert with the throttle, but will die when it contacts the tstop. Could the TPS be bad or is it able to disguise this IAC problem 8MUD? Great free advice, thanks you.

this is bizarre, I CANNOT MAKE IT DIE w/ this IAC plug disconnected from the throttle body. So, It'll die if reved for a second then slammed shut, but not if I depress the TPS plunger or disconnect the IAC>

I just called my grandson, who owned it before & does the things for me that I cannot see, he removed the TPS completely & then reinstalled it 2 weeks ago. He didn't know why he did that, he just did. He thought it might help it run better. I searched on the site & found the adjustment. I have no torx anything, so I cannot adjust it, but the output voltage is .50 volts & should be .62 volts according to the 13% of input rule. Did he not put it in right? Would this cause the DEATH-AT-IDLE?

Finally, The EGR seemed not to have any vacuum after the transducer, (if that's what that thing is, on the driver side fender) regardless of engine speed. That doesn't seem right. The TPS does read a smooth voltage gain w/ the motor off from idle position thru fully open throttle.

EGR is supposed to open mostly at higher RPM´s. They sometimes stick open and at lower RPM´s, this can stall the motor at stop lights and during low speed truns. Often the motor will die after releasing the gas pedal suddenly while sitting and idle erratically when the EGR is stuck open. Motor will run just fine with the EGR plugged off. Just messes with the smog test values some.
My last EGR (88) had a weak spring and would open, from just exhaust pressure. Also had a serious vacuum leak in the transducer on another occasion. My 87 didn´t have a tranducer (there are three types for the Renix that I know of, the 89 is supposed to be the cheapest), the EGR piston and rod got rusty and would stick open on occasion, causing stalling.
The defualt position for the EGR vacuum solenid is open, so when the solenoid is unplugged, there is constant vacuum to the EGR. The solenoid is on the inside of the fender well on the drivers side.
The IAC is mostly controlled by the O2 sensor. But the TPS, seems to have some kind of imput into the operation.
Vacuum leaks will mess with your idle. Though at least for me, vacuum leaks didn´t cause stalling, mostly erratic idle. The idle would hunt (up and down) and the motor would idle poorly (almost sounded like a miss).

If the TPS was out recently & unceromoniously jammed back in, it would be off. I don't know if the .12 volt difference would cause this, maybe the other guys know, but the problem started recently right? Coinciding w/ the TPS removal? It seems throttle position related, (IAC,TPS are dependent on that, & screwing w/ them makes it run?)

I usually adjust my TPS, on the tranny side (4 pole connector) and let the ECU computer side (3 pole) take care of itself. .5 volts does seem a little low, I´m guessing your imput voltage is around 4.65 volts, somewhere close to 0.6 volts at throttle closed position, sounds about right. Book recommends 0.8 volts.
I´m still guessing your IAC is sticking or you have a vacuum leak that is fooling your O2 sensor.
When it idles, does it idle steady?
I´d get the throttle linkage (butterfly) to close consistantly and clean the IAC before, I started adjusting any sensors.
Check the vacuum line to the MAP.
Do a suck test on the vacuum lines coming from the intake manifold.
Check the intake bolts for tightness.
Check the wires running from the front of the injector harness down the front of the motor, for chaffing or fried spots near the exhaust manifold.
Spray out all the connectors with a good electrical spray cleaner.
I usually check things systematically, the easy stuff first and do the sensors last.
My IAC was jammed and the Jeep dealer had bent the throttle stop to adjust the idle. Worked kind of. Changing the throttle stop and/or the throttle stop adjusting screw (allen head), with change your TPS values.
A good TPS adjustment made a wold of difference in mine, tranny shifts and acceleration (seemed like it added 20 HP).
Don´t try and do to many things at once, gets confusing. Write down some of your tests for future reference. Many of the snesors are interrelated, kind of infinite variables. Making sure the basics of the motor are correct (air filter, vacuum etc.) and the mechanical aspects (linkages and connectors) are correct, really helps to trace down sensor problems.
Just popped into my mind, but an oil covered air filter, will also seriously mess with your idle. One of those simple things that will drive you nuts.

Tonight I checked most of those things, 8MUD, & everythings about right. Air filter clean, MAP lines OK, wires tight, etc. The idle was steady but a little low (600 or so in park, should be 900), so I adjusted the throttle stop out until it idled at 900 & 750 in drive, & then adjusted the TPS to .81 volts. It no longer dies, & I cannot make it die the way I did last night (rev it then quickly close the throttle). I haven't driven it yet, but I sure would love 20 more HP! Thanks for the help.

It sounds like one of 2 things has happened now: Either you fixed what was wrong (TPS was not adjusted when reinstalled) OR you have simply masked the problem by raising the idle & fooling the ECU. Did you try to make it die after the TPS adjustment W/O raising the idle mechanically? The problem may still exist. We've all unknowingly (to some extent) changed one thing to reduce the influence of a different problem. Let us know how it drives, accelerates, & shifts...

There is another orifice in the top of the throttle body, adjusted by removing a pressed on cap on the side of the TB. I guess it is a fine, idle air adjustment. Mine is plugged up with old oil, but most ways seems to idle OK (so I haven´t messed with it).
Idle is temperature sensitive, the coolant temp. sensor on the lower drivers side of the block and the manifold temp. sensor both seem to have some imput, along with the physical amount of air (O2 sensor) passed through the throttle body through the butterfly stop adjustment, the IAC and the idle air orifice and vacuum leaks if any. Believe the MAP and the TPS also have some imput (a lot of variables to contend with).
TPS is two part, one half controls tranny shifts and other functions, the other half is to tell the ECU which position the throttle is in. The tranny side goes from a higher voltage to a lower voltage, the ECU side from a lower voltage to a higher voltage. And to throw another variable in to the adjustment procedure, the supply voltages for the two halves of the TPS, come from two different modules (they are rarley the same). Kind of amazing the computer manages to sort it all out and idle at all.
Jneary recommends a 12-14% setting on the TPS. I compromised on mine and ended up with a 3.9V +/- on the tranny side (which works well) and am still a little off on the ECU side, which seems a little low (but close enough).
My idle seems to go down, the warmer the motor gets, if I adjust the idle at operating temp. (above say 200) it idles a little too high (between about 140-180 or so), till it warms up, another compromise. For the first 15 seconds at start-up (high idle) and until the motor gets above around 140-160 (moderate idle/just a little higher than normal), above around 200 F normal idle (mine is usually around 700-750). Another factor is extended idle, computer switches to another set of parameters, which will/can change the idle also.

oldie eye said:

I just called my grandson, who owned it before & does the things for me that I cannot see, he removed the TPS completely & then reinstalled it 2 weeks ago. He didn't know why he did that, he just did. He thought it might help it run better. I searched on the site & found the adjustment. I have no torx anything, so I cannot adjust it, but the output voltage is .50 volts & should be .62 volts according to the 13% of input rule. Did he not put it in right? Would this cause the DEATH-AT-IDLE?

Click to expand...

I've had the same problem and the voltage is touchy, book sez .84 the factory sez .64, I think they want .84 because of line loss to the ecu. If you have accses to a mt2500 you can adjust it on the fly soto speak to the .64.
The EGR will only have vacuum at higher revs the solinoid will stay closed most of the time.
The air adjust and throtle body must be clean to get a good idle it may be a safe bet its carboned up.

Overthehill