sometimes it dies, sometimes it comes close,and when I get near home it runs like new

HJ88 · Jun 20, 2005

I've been having problems with the engine dying when I give it abit of throttle then take my foot completly off the gas, sometimes it goes back to idle, sometimes it goes down to 150 - 300rpm then back up to idle, and sometimes it just dies.. i've recently gotten a new ISSM (I think I messed mine up while cleaning it, while I was cleaning the TB) and I've readjusted the TPS to the correct reading... and it still dies.. now I'm thinking its the MAP sensor, perhaps not giving the correct response at lower rpm's and killing the engine... I've tested the input/output voltages on the MAPS and they come out fine (5.02v @ C, 4.82v @ B) but I dont have long enough probes to check the resistance between A and the ECU, although I suppose abit of wire would work so I'll try that tommorow.. (BTW, anyone know an easy way to check the wiring harness up to the ECU without pulling out the whole computer?)...

I've searched the boards and havent found anyone with quite the same problem (alotta people have Idle problems, but I can idle all day, just when I give it abit of gas while stopped then let off it wants to die or does..)

As always I appreciate all the help... I dont know how I'd get anything done without you guys (and gals)..

CheapXJ · Jun 20, 2005

forst and foremost, make sure that all the intake/exhaust manifold bolts are tight and there are no vacuum leaks.

check the ground going to the throttle positon sensor. if the resistance is over 1 ohm, then ground the TPS directly to the chassis.

does your Jeep have a large wiring connector on the firewall above the brake vacuum booster? if so, disassemble it and spray it with a healthy coating of ox gard.

if that doesn't clear it up, chrysler sells a crankshaft position sensor kit that includes an extension harness that bypasses that connnector (referred to as C101) go to the dealership, buy that kit and install it. I got one like 2 years ago and it was about $60, comes with a new crank sensor.

CheapXJ · Jun 20, 2005

I'm assuming you have an 88 cherokee by your username, and when you mention adjusting the throttle position sensor, it's gotta be an 87-90 'cause anything newer is non-adjustible

8Mud · Jun 20, 2005

Re: sometimes it dies, sometimes it comes close,and when I get near home it runs like new

Two posibilities that pop into mind are a sticky IAC and an EGR that has junk on the seat and is hanging open. Wifes old 87 had an EGR that was hung slightly open, the motor would often die at stops or during low speed turns. Sticky IAC is also a posibility, IAC is just about the only air you get when the throttle is closed, especially if the idle air adjuster/orifice is plugged with baked on oil. Unsticking an IAC can be a simple as dribbling a little light oil into the IAC orifice, with te motor running and working the throttle just a little.
A questionable 02 sensor will also do that. Somtimes the 02 sensor starts to fail it´s at higher RPM´s, sometimes at lower RPM´s.

HJ88 · Jun 20, 2005

Re: sometimes it dies, sometimes it comes close,and when I get near home it runs like new

yes it is an 88' with the 4.0.

refresh my memory of what the IAC (Idle Air Control valve, me thinks) is? isnt that what the Idle Speed Stepper Motor is? I just replaced that with one from napa (maybe thats the problem) and I had just recently cleaned out the whole TB, so everything should be clean... I'll tear it apart again and check anyway.. would it hurt the ISSM to spray some dura-lube or wd-40 on it just to lube it up abit?

And I've disconnected my EGR valve when I made my KN filter conversion.

and Where do I check the ground resistance to on the TPS? against the chassis or something?
and whats ox-guard? some sort of moisture displament spray? wouldnt wd40 work aswell? theres some sort of grease on the contacts of that connector and there doesnt appear to be any corrosion..

And I wouldn't doubt that the 02 sensor is getting faulty, I dont think its ever been changed (atleast I havent, and I doubt the previous owners have)..

thanks for the help

8Mud · Jun 20, 2005

Re: sometimes it dies, sometimes it comes close,and when I get near home it runs like new

With the ignition on, you can measure between the ground wire at the TPS and battery ground and see what you have for standing voltage. There is gonna be some, there is a resistance built into the TCU and the ECU. But excessive resistance in the TPS ground circuit (both sides, it is actually two TPS´s in one) will cause problems. The connector at the TPS, the 101 connector, the plug at the TCU or the ECU and the ground at the motor oil dipstick holder, are all possible spots for resistance. My TPS actually had low imput voltage, because somebody had sprayed WD 40 on the TPS connector. After cleaning the connector I had almost a volt more of imput voltage. I also ran an extra ground from the dipstick holder to the firewall (why not). And an extra ground from battery negative to the front clip (again why not). my 101 has no excess resistance, but if it ever does, I´m gonna solder the problem wires, around the connector.
WD 40 is a poor choice, it has some wax in it, that causes some resistance, you don´t need. The TPS circuit is fairly low voltage.
Idle air controller, idle air stepper motor and pretty much the same thing with different names. Perform the same function (basically), they adjust motor idle, by controlling the air flow at throttle closed. But actually work a little all the time, even with the throttle open. Idle air stepper motor in the old carburator Jeeps, actually helped control the fuel air ratio some, during normal operation.
The IAC controls idle, two diferent ways, depending on the motor temp. it has standard programed responces and after the 02 sensor kicks in, it operates on feedback, from the 02 sensor (and others).
Behind the plunger on the IAC, the is a notched rod that is coated in grease. Spraying it with oil may or may not help, doubtfull on a new IAC.
Where did you disconnect the EGR? The EGR has a piston that seats into the manifold, if the piston is gummed up it may not seat completely, the exhaust gases should only recirculate at higher RPM´s at low RPM´s or idle it really scews up the works.
Unplugging the electrical from the solenoid, doesn´t disconnect the EGR, it does just the opposite and makes it function continiously. The best spot to plug the EGR, is where the vacuum line plugs, into the EGR. Or possibly a cap or short piece of plugged vacuum line at the EGR solenoid. I had my EGR disconnected for awhile, but reconnected it, because of an upcoming smog inspection, noticed the motor temp. came down a bit, not much, but noticeable.
I had one EGR that had a weak or broken return. The exhaust gas, at fairly low RPM´s would push it open.
The last low idle situation I had, turned out to be the 02 sensor, the idle would get progressively lower the hotter the motor would get, at normal operating temp. it was just a few hundred RPM´s at idle. The motor temp. would go up and the tach at idle would go down.

Gunner · Jun 21, 2005

Re: sometimes it dies, sometimes it comes close,and when I get near home it runs like new

I am having similar/the same problems. If I give it gas and let off it almost dies, now when I put the motor under load between 1000 and 1500 RPM's it stumbles and tries to die. But its fine past that point. It's been very frustraiting, been messing with it for 2 weeks now. It's always idled a little high 1500 - 2000 so I adjusted the IAC to idle at 1000 and unplugged it. Must have been like that for a year and no problems. Plugged it back in and the problem is still there now it just idles high again and won't die when I let off. Still stumbles under load, (break stand slowly increasing the throttle) I have replaced the CTS,CPS, cap, rotor,wires and 02 sensor, because it was probably time, tested the MAP, MAT,TPS, Fuel, ballast resistor, relays, EGR, vacuum leaks and made sure the tranny was tight to the motor. I'm at my wits end. Any more ideas, I didn't touch the manifold bolts thats what I'll try next.

8Mud · Jun 21, 2005

Re: sometimes it dies, sometimes it comes close,and when I get near home it runs like new

Gunner said:
I am having similar/the same problems. If I give it gas and let off it almost dies, now when I put the motor under load between 1000 and 1500 RPM's it stumbles and tries to die. But its fine past that point. It's been very frustraiting, been messing with it for 2 weeks now. It's always idled a little high 1500 - 2000 so I adjusted the IAC to idle at 1000 and unplugged it. Must have been like that for a year and no problems. Plugged it back in and the problem is still there now it just idles high again and won't die when I let off. Still stumbles under load, (break stand slowly increasing the throttle) I have replaced the CTS,CPS, cap, rotor,wires and 02 sensor, because it was probably time, tested the MAP, MAT,TPS, Fuel, ballast resistor, relays, EGR, vacuum leaks and made sure the tranny was tight to the motor. I'm at my wits end. Any more ideas, I didn't touch the manifold bolts thats what I'll try next.

02 sensor heater relay and/or fried wiring where it exits the fuel rail harness and goes over the front of the motor and back underneath (very near the exhaust manifold). The Block temp. sensor, 02 sensor and knock sensor harness. May be a possiblilty for the stumble. A heater circuit test for the 02 sensor is pretty easy. Your 02 sensor and 02 heater relay may be good, but how are the wires and connectors?
The 1500-2000 RPM idle sure sounds like the hose to your vacuum canister is disconnected. The like 3/8" size vacuum line that exits near the rear of the intake manifold and goes all the way around the engine compartment, under the battery box (look close here) and to the canister behind the bumper on the right side. You can plug the large vacuum outlet at the manifold (for a test), its for the heater and cruise control vacuum circuit. A hissing at the brake, vacuum booster is also a possibility for a major vacuum leak. If you have a vacuum gauge, what is your vacuum at idle?
Just a side note, for every sensor/or ignition component problem I´ve found, I´ve found 4 or 5 wiring or connector problems. I rarley change a sensor (or componenet), until I´m relatively sure the problem, isn´t in the wiring.

Gunner · Jun 21, 2005

Re: sometimes it dies, sometimes it comes close,and when I get near home it runs like new

Thanks for the tips I'll go chasing wires tonight. I know it has to be something reletively simple. I just can't pinpoint the problem. The vacuum canister has been mounted under my hood since day one, I put a tube bumper on it and had to put it somehwhere.. Now that I think of it, the high idle started after I cleaned the intake, about 3 years ago. Never been the same since. I'll check the wires and see what I come up with. Thanks again for the tips.

HJ88 · Jun 21, 2005

Re: sometimes it dies, sometimes it comes close,and when I get near home it runs like new

8Mud said:
With the ignition on, you can measure between the ground wire at the TPS and battery ground and see what you have for standing voltage. There is gonna be some, there is a resistance built into the TCU and the ECU. But excessive resistance in the TPS ground circuit (both sides, it is actually two TPS´s in one) will cause problems. The connector at the TPS, the 101 connector, the plug at the TCU or the ECU and the ground at the motor oil dipstick holder, are all possible spots for resistance. My TPS actually had low imput voltage, because somebody had sprayed WD 40 on the TPS connector. After cleaning the connector I had almost a volt more of imput voltage. I also ran an extra ground from the dipstick holder to the firewall (why not). And an extra ground from battery negative to the front clip (again why not). my 101 has no excess resistance, but if it ever does, I´m gonna solder the problem wires, around the connector.
WD 40 is a poor choice, it has some wax in it, that causes some resistance, you don´t need. The TPS circuit is fairly low voltage.
Idle air controller, idle air stepper motor and pretty much the same thing with different names. Perform the same function (basically), they adjust motor idle, by controlling the air flow at throttle closed. But actually work a little all the time, even with the throttle open. Idle air stepper motor in the old carburator Jeeps, actually helped control the fuel air ratio some, during normal operation.
The IAC controls idle, two diferent ways, depending on the motor temp. it has standard programed responces and after the 02 sensor kicks in, it operates on feedback, from the 02 sensor (and others).
Behind the plunger on the IAC, the is a notched rod that is coated in grease. Spraying it with oil may or may not help, doubtfull on a new IAC.
Where did you disconnect the EGR? The EGR has a piston that seats into the manifold, if the piston is gummed up it may not seat completely, the exhaust gases should only recirculate at higher RPM´s at low RPM´s or idle it really scews up the works.
Unplugging the electrical from the solenoid, doesn´t disconnect the EGR, it does just the opposite and makes it function continiously. The best spot to plug the EGR, is where the vacuum line plugs, into the EGR. Or possibly a cap or short piece of plugged vacuum line at the EGR solenoid. I had my EGR disconnected for awhile, but reconnected it, because of an upcoming smog inspection, noticed the motor temp. came down a bit, not much, but noticeable.
I had one EGR that had a weak or broken return. The exhaust gas, at fairly low RPM´s would push it open.
The last low idle situation I had, turned out to be the 02 sensor, the idle would get progressively lower the hotter the motor would get, at normal operating temp. it was just a few hundred RPM´s at idle. The motor temp. would go up and the tach at idle would go down.

I have my EGR plugged at the vacuum source (port C).. perhaps this is the wrong place?

and with the TPS ground.. my multimeter is a cheap-ass radio shack version that is pretty much impossible to read... it could be anywhere between 1.8 - 103,000 ohms... according to the meter

would it be OK to just run another wire straight from the block at the dipstick holder right to the ground at the TPS (both grounds (I have an auto))?

Gunner · Jun 23, 2005

Re: sometimes it dies, sometimes it comes close,and when I get near home it runs like new

There is 1 thing I can guaranty, it's not the O2 sensor, the CTS, or the Knock sensor, because they are all disconnected and the jeep runs fine but still pulls the same crap, now mostly in reverse., I chased wires for hours and found nothing. If it was a daily driver it would be fine but rockcrawling it's stumbling right where I need it most. The intake was tight and the more stuff I unplugged it got better.... WHat a pain. Don't have a vacuum guage so that might be the next adition to the tool box.

Gunner · Jun 30, 2005

Re: sometimes it dies, sometimes it comes close,and when I get near home it runs like new

Alrighty, don't know what the hell happened but I pretty much gutted the jeep last weekend, found 1 stinkin wire that was worn through. It was the + wire from the battery to the "electric distribution" center thing. Not sure what its called. Its right next to the relays. Of coarse I started on the drivers side so it took a while to get there. Anyway fixed that wire and it hasn't done it since. So I guess I'll find out if that was it. Took it out to the desert a few minutes ago, seemed to idle a little high but other than that seemed perfect. I just hope it doesn't coem back..

Thanks for the tips guys

csr_011 · Jul 8, 2005

Re: sometimes it dies, sometimes it comes close,and when I get near home it runs like new

Alright Gunner,

I was doing the wire hunt again today, discovered loose contacts in the starter relay and a corroded solenoid wire(the one on the relaty in the center below the + stud full of wires). Tried to get a new relay, no luck for 87 4.0's at Advance Auto, well, got one, but the girl behind the counter gave me one for an 86 2.8...NOT THE SAME RELAY??? So, i just cut the wire back and put the original back in till i can get to the dealer or whatnot...

Also cut the CPS connectors out and wired the CPS straight to the harness, didnt help any, so im either going to get some good all weather connectors as mentioned in other posts for a permanent replacement or just clean up the old ones and put them back in...

Havent gotten underneath yet and wiggled harnesses until it dies though.

Have narrowed it down a bit though. Has to be a healthy bump to the rear wheels to kill it, mostly on turns, but not limited too...

Cory

sometimes it dies, sometimes it comes close,and when I get near home it runs like new

HJ88

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CheapXJ

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CheapXJ

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8Mud

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HJ88

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8Mud

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Gunner

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8Mud

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