Jeep Intermittently Stays running.. Please Read / Give Advise

[Muad'Dib]

I got the throttle body that im using now from a Junk yard jeep. It looked like it had a slight engine fire... nothing looked extremely burnt, but you could see the shit from the fire extinguisher.
I took it off the old jeep and took it home.
When i got home, i completely dissambled it. I individually cleaned up each peice. I made sure the valve was flat and everything cleaned up real well. When i initially installed everything, i didnt have this problem .. its only recently that i have.

Ill try the battery thing the next time i have the hood open... and see what happens.

As a test try giving the gas peddle just little gas (actually air) before and during the start up cycle to see if the problem is too little idle and start up air supply. IF taht works then keep focused on the IAC-throttle body and idle stop screw as the problem-solution.

Damn i should of thought of this.... ill give it a shot tomorrow.

As far as the +B latch relay, i guess its a stong possibility that something is wrong with the circuit. I replaced the relay here with a SPST 4 pin, i have BOSCH replacements on order. Its doubtful that after replacing the relay that its not working again, unless like i said there is something wrong with the circuit.
The above also makes since because lets say if i start the Jeep, and then shut it off (or it dies) then restart it, the second start (now that i did everything in my previous post) is just as it should be. RPM's jump to approx 1500, and then down to ~750.
Whatcha think?

 

[Muad'Dib]

Also, how would i test the circuit for the +B latch relay.... or am i just avoding the truth that after approx 1 year my IAC is shot again!

 

[Ecomike]

Sounds to me like your on the right track now. Don't forget, at some point that the IAC itself could be sticking, even a new one can go bad, but it sure sounds like the Relay, or the wiring between it and the IAC, or something odd with that throttle body. I have heard of weird unresolved problems solved by replacing the throttle body, where the problem with the bad throttle body was never isolated.

There are two factory adjustment points on the throttle body, the one you have adjusted, and a second hidden a cap on the drivers side. I never messed with the capped one, but if the cap is missing, the prior user might have messed with it!

Let us know how its progressing!

IAC +B latch relay test, takes two people and an ohm meter. lawsoncl might know the right wires, I will look and see if I have it. Basically it is my understanding that +B latch relay keeps the ECU and IAC alive after the engine stops, ECU confirms that somehow and then cycles the IAC to some specific start location. So might be several possible things to check.

 

[Ecomike]

Looking at haynes, it is DPDT relay, so it may need that 5 pin relay you and 5-90 discussed.

It has 5 wires going to the relay! The red wire is always HOT!
The 2 pink wires go to the ECU, and the Blk/Wht wire goes to the diagnostic connector and the ECU.

4 wires go from the ECU to the IAC, Red/Yel, Blu/Yel, Grn/Blk, and Pnk/Blk. That is all the Haynes lists. The FSM may have better info, such as wire tests. FSM, battery voltage goes to pin 1, +B latched is to pin 5 while engine is running and for 2 to 5 seconds after ignition is shut off. PIn 4 is to the diagnostic connector #B10, latch relay ground is pin 2 and goes to diagnostic connector A9. Pin 3, the middle pin is not used!!!!!! FSM says the ECU continues to energize the +B latch relay for 2 to 5 seconds after the KEY has been turned OFF. Time delay allows the ECU to repostion the IAC in anticipation of the next start up. Beyond that you are on your own!:scared:

 

[Muad'Dib]

DPDT or SPDT?? From what you described it sounds like SPDT...

Anyway, i just got back from lunch, and here is what i found out.
The Jeep is running much much better now, and the idle is perfect in or out of gear after being driven.
Still the problem with the idle at start. I tried pushing my foot on the gas peddle just a tiny bit to let more air into the intake when i start it. It reved up to about 3000, and i let off the pedal. It then almost immediately dropped down to the first line on the tach and stayed there. (acting as it has been).
I havent got a chance yet to see if when started if the idle slowly goes up to normal or not. Today ive only had a chance to hop in and drive. I do know that after about hitting the first couple stop signs the idle is perfect. (basically after driving)

So Ecomike, it sounds as if its down to either the IAC, The +B latch relay, or the +b latch relay circuit. Does that sound right?

 

[Ecomike]

DPDT or SPDT?? From what you described it sounds like SPDT...

Anyway, i just got back from lunch, and here is what i found out.
The Jeep is running much much better now, and the idle is perfect in or out of gear after being driven.
Still the problem with the idle at start. I tried pushing my foot on the gas peddle just a tiny bit to let more air into the intake when i start it. It reved up to about 3000, and i let off the pedal. It then almost immediately dropped down to the first line on the tach and stayed there. (acting as it has been).
I havent got a chance yet to see if when started if the idle slowly goes up to normal or not. Today ive only had a chance to hop in and drive. I do know that after about hitting the first couple stop signs the idle is perfect. (basically after driving)

So Ecomike, it sounds as if its down to either the IAC, The +B latch relay, or the +b latch relay circuit. Does that sound right?

Sounds like the IAC is working once it gets going, but they can stick and unstick but yours is predictable, so I would the IAC may be OK, hard to say for sure. Could still be more adjustment needed on that throttle plate screw too, but try that last, and be sure to reset the TPS again if you do adjust it more.

I am not sure if its DPDT or SPDT.

 

[Muad'Dib]

Right now i have a SPST relay in that location. Thats probably whats going on. Its not backing off of the TB until after a bit... causing the low idle.

As i said previously i have some BOSCH's on order. I still have some old ones laying around... ill put one in and see what happens!

 

[Muad'Dib]

Ok ive made alot of progress i would say.. Here is where we are at.
Still waiting on BOSCH / TYCO relays .. no biggie.

Engine cold from sitting overnight.. start then dies 4 seconds later, starts again stays running with low idle.
After running / warming up low idle persists.
If i drive it, the idle becomes immediately good (after being warmed up, havent tested when cold)
After being warmed up and driven if i stop and turn it off, wait a few seconds and start it again, the idle is just a tad on the low side then resumes to normal idle.
After being warmed up and driven if i stop and turn it off, then wait 5 minutes and turn it on again, the idle is low. If i give it a little gas and let it rev up to approx 1500-2000 RPM's and then let it come down, its at normal idle.

What do you think now?

 

[Ecomike]

Ok ive made alot of progress i would say.. Here is where we are at.
Still waiting on BOSCH / TYCO relays .. no biggie.

Engine cold from sitting overnight.. start then dies 4 seconds later, starts again stays running with low idle.
After running / warming up low idle persists.
If i drive it, the idle becomes immediately good (after being warmed up, havent tested when cold)
After being warmed up and driven if i stop and turn it off, wait a few seconds and start it again, the idle is just a tad on the low side then resumes to normal idle.
After being warmed up and driven if i stop and turn it off, then wait 5 minutes and turn it on again, the idle is low. If i give it a little gas and let it rev up to approx 1500-2000 RPM's and then let it come down, its at normal idle.

What do you think now?

In addition to the possibilities you are checking out, If you had not already tested and ruled out the CTS and MAT temperature sensors, I would suspect the MAT sensor, or a thermally variable ground resistance on the TPS.

If I am right on one of the prior targets, like the throttle body idle stop, I am guessing that maybe the ECU is using a data table of some sort that is causing the low idle, maybe based on an assumption of the proper IAC location, which may be hindered by a previously messed with throttle body tab-screw stop on the idle, and then later, once you start driving maybe the O2 sensor (or something) kicks in and helps the ECU reset a table value that the ECU uses to reset the IAC, but I am really grabbing at straws with that analysis. Many people have manually adjusted the idle stop on the throttle body to fix a high idle caused by common vacuum CCV line leaks, and since your throttle body came from a junk yard, I am guessing it might be the culprit. Did you fix a vacuum leak after replacing the throttle body perhaps???? If yes the combination might have caused your problem.

 

[Muad'Dib]

Naa, all my vacuum leaks have been fixed for some time now... and ive checked again this time around to make sure nothing else has arrisen.


Were you saying that you think its the MAT sensor in the begining of your last post? I checket that and it ohmed out to spec. I havent checked the 02 sensor or the CTS yet. The CTS is about 1 month old if that, and the 02 sensor is about a year old.
Your thinking its the throttle body?

 

[Ecomike]

Naa, all my vacuum leaks have been fixed for some time now... and ive checked again this time around to make sure nothing else has arrisen.


Were you saying that you think its the MAT sensor in the begining of your last post? I checket that and it ohmed out to spec. I havent checked the 02 sensor or the CTS yet. The CTS is about 1 month old if that, and the 02 sensor is about a year old.
Your thinking its the throttle body?

I had cold weather starting problems with mine when the MAT sensor died on mine. You said you checked yours but did you check it at say 30 F, 70 F and 140 F, or thereabouts? IF you checked it at just one temperature, say hot, you need check it cold too, as it may be stuck at the test temperature you tested it at. I seriously doubt its the O2 sensor.

You said you thought the throttle body was OK, because the problem did not start right after changing the throttle body. How soon after did it start?

The ECU (Renix) does store, and gradually write over old sensor data like old TPS idle voltages, and it uses an average of those data paoints for the real idle position in its moving data base. There could have been a short delay in the throttle body problem manifesting itself due to that memory update time delay. Also, if there was a small vacuum leak right after replacing the throttle body that you later fixed, reattached later and forgot about, that could have delayed the throttle body display of a low idle, as the extra vacuum leak air could have helped hold the idle higher. I still think it is the throttle body, perhaps something, some dirt or trash, up deep inside of the idle air port came loose later, after installation and after running properly for a while. The fact that adjusting that idle throttle stop some on the throttle body helped some is still quite significant. I am just trying to make sense of the delay in the problem start up after swapping out the throttle body. Did you replace the TPS or something like it after replacing the throtlle body? Perhaps something (trash, burr,??) was holding the throttle plate open a tinny bit more that finally came loose a short while after installing the throttle body?

The problem is so repeatable, that I am starting to doubt it is the IAC or +B latch relay because you say it starts working fine after you first hit the gas peddle. The +B latch relay is on all the time while running and 2-5 seconds after shut down, so if the idle is perfect after hitting the gas peddle it starts really narrowing things down. Perhaps the ECU switches to using the O2 sensor and a different data table and algorithm right after you press that gas peddle, and resets the IAC, in which case the IAC itself would OK.

 

[Muad'Dib]

I did check both the MAT and the CPS when cold and hot. The MAT tested perfect, the CPS however didnt seem to fluctuate any... is it supposed to depending on temperature? ... i didnt think so.
I cleaned up the TB really well. I doubt that anything "broke free". I have about 3 TPS's laying around, and when i swapped in this TB, i did put in a different TPS.
Im not sure how long after i did the swap when i started to get the problem. Maybe a week or two? Not sure really.

I did a cold test this morning. Before the Heat started to get hot inside the Jeep, i tried to press the gas to about 1500-2500 RPM's and then let the idle resume. It was low. It would only start idleing better with this method if it was warmed up... or in closed loop. If in open loop, or while cold the idle is low no matter what. This makes me think its sensor related. What sensor feeds the ECU during open loop and not in closed loop??

THis behavior is very strange ...lol i do appreciate all the help.

 

[Ecomike]

I did check both the MAT and the CPS when cold and hot. The MAT tested perfect, the CPS however didnt seem to fluctuate any... is it supposed to depending on temperature? ... i didnt think so.
I cleaned up the TB really well. I doubt that anything "broke free". I have about 3 TPS's laying around, and when i swapped in this TB, i did put in a different TPS.
Im not sure how long after i did the swap when i started to get the problem. Maybe a week or two? Not sure really.

I did a cold test this morning. Before the Heat started to get hot inside the Jeep, i tried to press the gas to about 1500-2500 RPM's and then let the idle resume. It was low. It would only start idleing better with this method if it was warmed up... or in closed loop. If in open loop, or while cold the idle is low no matter what. This makes me think its sensor related. What sensor feeds the ECU during open loop and not in closed loop??

THis behavior is very strange ...lol i do appreciate all the help.

The MAT and CTS are exactly the same part internally!!!! They are variable resistors. The resistance varies with temperature as follows:

They should read as follows using an ohm meter, power off, wiring harness disconnected:

0 F: 25,000 ohms
20 F: 13,500 ohms
40 F: 7,500 ohms
70 F: 3,400 ohms
100 F: 1,600 ohms
160 F: 450 ohms
212 F: 185 ohms.

 

[Muad'Dib]

I havent checked the CTS yet, its not more then a month old. (replaced it when i had the head off fixing a broken stud, and stripped head) I said CPS because i meant CPS

As i said throughout this thread the only things i have not ohmed out per FSM are the CTS, and 02 Sensor. Only because the owner of the house im renting is building a plane in the garage, and there is 4 feet of snow on the ground. I REALLY dont want to lay underneath the Jeep in the snow to test those two sensors right now...

 

[corbinafly]

I did check both the MAT and the CPS when cold and hot. The MAT tested perfect, the CPS however didnt seem to fluctuate any... is it supposed to depending on temperature? ... i didnt think so.
I cleaned up the TB really well. I doubt that anything "broke free". I have about 3 TPS's laying around, and when i swapped in this TB, i did put in a different TPS.
Im not sure how long after i did the swap when i started to get the problem. Maybe a week or two? Not sure really.

I did a cold test this morning. Before the Heat started to get hot inside the Jeep, i tried to press the gas to about 1500-2500 RPM's and then let the idle resume. It was low. It would only start idleing better with this method if it was warmed up... or in closed loop. If in open loop, or while cold the idle is low no matter what. This makes me think its sensor related. What sensor feeds the ECU during open loop and not in closed loop??

THis behavior is very strange ...lol i do appreciate all the help.

All except the O2 sensor.

 

[Muad'Dib]

Well, i got my relays yesterday. My GF and I had drinks and dinner last night, and after we got home and watched LOST, i replaced all my relays. (4 in the passenger side strip by battery and the 1 for the fan on the drivers side).

Started the Jeep it idled low like it has been. Turned it off, and started it again.... started perfect! Turned it off and started it again a few more times ran muy perfecto.

Let it sit overnight and started it the next morning. Started and stayed running. It hasnt done that for a few mornings now so thats a great sign. Hopped in the Jeep after i got ready for work, and the idle was just a tad low. At lunch, the Jeep started and idled perfect. After it warmed up, it would idle a tad low... but it seems that it was getting slowly better.

At this point i would say that my problems are fixed now due to a bad relay (or more then 1). Its also slightly possible that some wiring under this relay area is messed up... but i really dont think so. I will however be able to tell with time... and i will definetly post back here a week to two weeks from now to give an update.

The puzzling thing is that when i looked at where my Relays go into the Jeep (and seeing how far my screwdriver would go down each slot), the only one that looks like it takes a 5 prong SPDT relay is the one for the 02 sensor. I will look again the next time i can inspect them better, but i swear it was the only one. It just leads me to believe that these idle problems were cause by the 02 Sensor's Relay.

It seems that i started with a bad relay for the fuel pump. Then i must have either had another bad relay, or swapped the bad one to 02 sensor causing the low idles. OR i bought a bad SPST relay from Radio Shack, and it was not working the IAC correctly.
I wont ever really know for sure what exact combintation it was, but its an inexpensive fix to get yourself ALL NEW SPDT relays. Seems to have fixed it for me.


Thanks everyone for all your help.

 

[Ecomike]

Well, i got my relays yesterday. My GF and I had drinks and dinner last night, and after we got home and watched LOST, i replaced all my relays. (4 in the passenger side strip by battery and the 1 for the fan on the drivers side).

Started the Jeep it idled low like it has been. Turned it off, and started it again.... started perfect! Turned it off and started it again a few more times ran muy perfecto.

Let it sit overnight and started it the next morning. Started and stayed running. It hasnt done that for a few mornings now so thats a great sign. Hopped in the Jeep after i got ready for work, and the idle was just a tad low. At lunch, the Jeep started and idled perfect. After it warmed up, it would idle a tad low... but it seems that it was getting slowly better.

At this point i would say that my problems are fixed now due to a bad relay (or more then 1). Its also slightly possible that some wiring under this relay area is messed up... but i really dont think so. I will however be able to tell with time... and i will definetly post back here a week to two weeks from now to give an update.

The puzzling thing is that when i looked at where my Relays go into the Jeep (and seeing how far my screwdriver would go down each slot), the only one that looks like it takes a 5 prong SPDT relay is the one for the 02 sensor. I will look again the next time i can inspect them better, but i swear it was the only one. It just leads me to believe that these idle problems were cause by the 02 Sensor's Relay.

It seems that i started with a bad relay for the fuel pump. Then i must have either had another bad relay, or swapped the bad one to 02 sensor causing the low idles. OR i bought a bad SPST relay from Radio Shack, and it was not working the IAC correctly.
I wont ever really know for sure what exact combintation it was, but its an inexpensive fix to get yourself ALL NEW SPDT relays. Seems to have fixed it for me.


Thanks everyone for all your help.

Dude! Your LOST! :eyes: It wasn't the girlfriend, the drinks or the relays that did it, it was the ISLAND, fate!! :guitar: :laugh: LOL.

Good work, glad to hear it solved the problem!

 

[Gritts]

:wave1: I have to ask (maybe I missed it somewhere) did you get your heat fixed?????

 

[Muad'Dib]

As i mentioned in this post (page 3), this was my third time flushing the heater core.

The heat would be great after doing so, but about a week later the heat would start to fade (im 99.9999% positive the core keeps getting clogged).

I DID this time replace the heater valve. So far so good. If the heat starts to fade out (again) i am going to try flushing one more time. If it still continues to get clogged up and fade im going to replace the heater core. Its not uncommon for them to keep getting clogged since what clogs them in the first place is corrosive. Im just thankfull that i dont have a leak because of flushing it!

 

[8Mud]

I pulled up my relay block and turned it over for a look see (underneath) it looked like a piece of cheese that had been lost in the back of the refrigerator for a year or so. I cleaned it out with a toothbrush some brake cleaner and lastly a quality contact spray, repacked it with die electric grease. Between cleaning the fuse block, the IAC and replacing the relays with Bosch, it's been a long time since I've had any significant high or low idle problems at startup. Mine does exactly like it is supposed to do, idles up monetarily at start up settles in to a cold idle (just a little high) then after awhile into a warm idle and stays pretty much stable.