Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

Good to hear - you've been fighting that for awhile now.

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

That's excellent to hear. I have two co-workers that have both been having rough and high idle problems. they both have 90 and/or 91's.

Question, what diagnostics can you run on a 90? I didn't think they were even OBDI compliant?

Thanks,
Kent

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

Hey Tuck, this will be a great help to many in the future. Do you happen to have a pic of your splce job?

Mick

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

There's 2 harnesses coming out of the TPS: the "square" 4 pin goes to the trannie to tell it when/how to shift and the 3 pin. This one is the important one. One wire has to have a 5 volt baseline, the next is the variance voltage that tells the computer how much throttle you're giving it, and the 3rd line is the ground. I assumed because the TPS was bolted to the trottle, it was grounded to the motor already, but the voltage is too low to chance that, so it's grounded in the harness' common ground. The wires are blue, grey and black. All he did was crimp a blue plastic "piggy back" clip on the ground-wire, and ran another ground wire out to a crimped on ring and mounted it on the bolt that has the grounding strap on the passenger's side of the motor.
According to his machine's footnotes, they recalled that TPS years ago. (So if you still have the original one, it may actually be FREE from Jeep.) The original front rotors were recalled too.

He said that when he encounters bad ideling on those '88-'90 6 cylinder engines or odd RPM problems, to go ahead and reinforce the ground at the TPS. It couldn't hurt and eliminates the TPS if it didn't help. These year model TPS' also have to be adjusted upon installation, like a distributer. You have to use a volt meter to get your baseline voltage to 5 volts or it won't run right either.

But I have to say this: It has NEVER ran this smooth, strong or gotten as good gas milage from just adding a ground wire. I'll go look tomorrow and see what color the Ground-wire was.

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

A: lblue/black - grey
B: dbrown/white - black (ground)
C: yellow/green - blue

More info:
HERE ,
HERE
and HERE .

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

I tried this trick on my 89 4.0 M.T and after the ground wire was piggy backed and the moter was started it immediatly ran up to a 3,000 rpm idle. I checked the voltage on the tps and it was fine 5v input and .8 on the output. I took it back off but this is really frustrating me to no end.

Jeep dealer ran test and said o2 reading was 0 so that was replaced, also said that the temp sensor was reading wrong but not sure which one because the one he ordered does not fit on my radiator.

89 Cherokee Sport
225,000 still kicking (??)
3" Rancho Borla headers and cat back

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

Depends on what temp sensor he meant. Tempsensor for gauge is on the head near the fire wall, tempsensor for the AC is on the rad, temp sensor for the ECU is low on the passenger side of the engine. If it's about the ECU, you'll need to replace the latter.

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

Thanks for the info, do you have any other opinions about the hesitation and bad idle?? Thinking that the TPS is just bad because when you start it it doesnt react to the throttle when you push it. Anything under 3,000 rpms on initial startup and there is no response, it peaks and then slowly dies. unless it hits 3, then even tho its high you have response to the throttle. Help Please.

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

not trying to beat this to death, but Nix, in your writeup you say output should be 16% of the input voltage. in AJ's post he says ratio of output over input should be .83, which means output should be 83% of input voltage.

i notice NIX's was for a manual and AJs for an auto. maybe i am thinking wrong, or they should in fact be different.

BTW i am out messing with mine right now. manual transmission, input is 6.4 volts, output is .14 volts, thats 2%, guess i need some adjusting! my problem isnt so much high idle (yes it idles high after hard or cold starts, and if i start it while its in gear, i.e. when im wheeling and im in a tricky spot, in 4low of course

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

To be honest, it confused me also.

This is my favorite as I have a manual. In the same thread as AJ's answer, Krabysniper also describes the procedure from 5v input and 0.8v output. The colors of the wires just didn't match mine until I found out to look futher into the harness. If you read the output, when you openthe throttle it should go higher, without any out of line readings or flat spots. I believe the FSM also says to measure this way. In my former post I wrote the colors of the wires, because sometimes it differs a bit from the sensor to the rest of the harness, but on the harness itself, it's all the same, auto or manual, so you'll always find the right wires to probe. Auto's have the double setup, that's the main difference.

In your case, input probably can't be adjusted, just take it as it is. I have the same thing in my MAP input. The output should be adjusted and if not possible you might think of replacing the TPS.

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

I guess you're right about the TPS, as you get no response from it. I would almost say you need the extra ground. Did you check all your other grounds? They bolt up on the passenger side of the engine. 4 Thin wires, the minus from the batterie an I probably forget one. But the extra ground wire shouldn't cause a problem, so you can leave it. It's more an elimination of a problem caused by bad ground.

Other causes of bad idling are:
- air stepper motor;
- clogged idle port in throttle body ;
- loose or warped TB
- cracked or loose or cloggedup vac lines;
- bad EGR and EGR regulator valve;
- CPS;
- rotor, cap, plugs, wires.

I'd first have the engine respond to the throttle (TPS) before trying lots of probably not necessary replacements and mods. But assuring everything works allright is always good. Especially vac leaks cause funny idle behaviour. Mostly repairing them costs little or no money, but sometimes they are difficult to find. One time I had an O-ring missing in a new vacuum harness connector.

Just some extra info about sensors .

BTW: the temp sensor in your earlier post is probably to replace the one on the block, so it won't fit the rad. If it's bad it should be replaced, because the ECU will think your engine is still cold and lets the engine run on the cold engine program. I don't think, however that it causes the idling problem, as all engines have to make cold starts (and not all of them start idling like crazy)...

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

well, i adjusted it to 16% of 6.4 which is approx 1 volt.. way too high idle, 2000rpm copld, then i drove it for about 5 mintues and it went up to 2500 rpm and stayed there. so i added the extra ground, no help at all. then when i checked the input voltage, it was up to 9 volts! so i just put it at a low output voltage. i keep the multimeter in my car as well as a full toolkit, so if its wrong i can fix it on the fly. my guess is the input varies.. maybe tomorrow ill try running 5 volts straight from the battery or fusebox. another idea is during a time where it is idling high is to check the input voltage, maybe it fluctuates.. i dont know.. another day another mystery!

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

Check the input on your MAP sensor. It should also be 5v. Something is definately wrong at your TPS input. At least you know where to start. I have no idea however where the thingy is that makes the 5v input. If it can't be cured I'd use the MAP input. But it wouldn't surprise me if it also won't get a steady 5v. Maybe the adjustable MAP input is an idea to provide a steady 5v source, but this where you start tinkering. If it were my rig i'd find out where the problem of the fluctuating original 5v input is caused.

Why aren't you asleep?

It's 10.00 AM over here....

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

yeah, i was thinking of tracing the wire back.. but it will inevitably go through some electronic module that no one has much of an understanding of. maybe i should jsut work on my lawnmower.. though its not broken.. i can fix that.

well, i dont sleep much.. probably go to bed around 4 am and wake up at 7:30 or 8am.. i get it from my father. he goes to bed at midnight and wakes up at 3 and goes to work every morning!

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

In reply to:

maybe i should jsut work on my lawnmower.. though its not broken.. i can fix that

[/ QUOTE ] Or you can use it to mow the gras. It's always nice to have a nice decent yard. I'm sure your neighbours will like it when they go to work and see that tidy grass....

In reply to:

probably go to bed around 4 am and wake up at 7:30 or 8am

[/ QUOTE ]
About the sleep thingy: did that many times, but always had to pay later.

You know you're not the only poster on this board, sitting behind his screen on weird times? I still wonder where to get the extra time I always need so bad, but after a week with only 3-4 hrs a night I start blowing bubbles...o0O

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

yeah, i paid already.. 4000 dollars. when i was 17 i totaled my 87 XJ.. working 75 hours a week, and partying with my friends the rest. no, it wasnt drinking and driving; it was SLEEPING and driving (no alcohol involved). just a short 7 mile drive from my friends house to my house.. but it wasnt short enough.
75+ mph (in a 55 zone, i cant remember much except getting in my car at my friends house) + falling asleep (its easier than i would have ever thought) going off the road + no seatbelt = 1 rolled XJ + 4 cop cars + 1 fire truck + 1 ambulance + 200$ fine + 4 points off my license + 1 big fat lip + one very lucky kid.

it was a 4 corner roll, sideways end over end.. i remember them askign me what happened and i couldnt recall.. because it was jsut sitting there in the marsh below the road.. looked like had just been plopped there. and in a few minutes we figured out it had. the last roll it dug in and bounced over 20 feet (in one bounce [should i say bounce? metal doesnt bounce all that well]) to where it landed against a water culvert. dont sleep and drive, whatever you do.

 

Re: \'90 XJ\'s CURES CRAZY IDLE FINALLY......

So, voila the parts XJ...