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#26 06-16-2011 11:30:32

Danuc
Helper
From: Virginia
Registered: 02-25-2010
Posts: 20

Re: my idle issue

low idle
very rough idle
idling high
high idle

Everything you mention is related to idle. I'm assuming it runs fine
otherwise?

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06-16-2011 11:30:32

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Re: my idle issue

#27 06-16-2011 11:38:44

bj
Rookie
Registered: 05-18-2009
Posts: 88

Re: my idle issue

when it's idling fine it runs perfect, good power, good pull through the gears.
when it's idling high it misfires a little and doesnt pull thru the gears like it should.

so today i swap out the CPS.  crank/crank/crank no fire.  i pull the end off the connector & crimp the wires together with a butt connector.  crank/crank/crank no fire.  boo this.  i start beating on the CPS to get it closer to the flywheel & blah.  crank/crank/crank no fire.  so i cut the butts off & solder the wires together.  crank/crank start.  yea!

drove it up to the store, idling fine, a/c on high.  come out start it up and it shoots up to 2500rpm, holding steady.  i shut it off, start it again, 2500rpm....mutherfawker.  shut it off & start it again, 650rpm......

what the fawk!?!1

it must be my variable vacuum leak system has a fault.?

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#28 06-16-2011 13:42:24

loohotel
Newbie
Registered: 03-01-2009
Posts: 7

Re: my idle issue

" variable vacuum leak system " Nice definition!!  I have that installed in my '89, too, but not as reliably as yours... I think mine's aftermarket (at 197K miles, who knows what the Gremlins put in there! Ahhh... there's the problem... AMC Jeep; AMC Gremlin... Now, I get it!!

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#29 06-16-2011 13:45:20

seven
Helper
Registered: 02-10-2009
Posts: 20

Re: my idle issue

When you have the high idle problem (ie 2500 rpms) check the voltage at the TPS.
IF the output voltage is .5V or around there.... then the TPS is not the problem... IF you read something like 2.5V; the there is your problem OR.... maybe just another symptom....
There are a few things that could cause these symptoms...
IAC receiving signal from the ECU to create high idle, a short in the IAC wiring....internal to the harness, or a short in the TPS wiring indicating to the ECU; that the throttle is at other than idle...

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06-16-2011 13:45:20

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Re: my idle issue

#30 06-21-2011 09:25:22

bj
Rookie
Registered: 05-18-2009
Posts: 88

Re: my idle issue

k, more info.

checked voltage at the TPS.  it's the same with engine running or not, 4.69 in and 3.83 out which is right at .8% so it's correct.

i disconnected the IAC just to make sure that wasn't a factor.  the engine idled at 750 for a few minutes and then ran up to 2500 again.  restart & it was a perfect 750.  i started wiggling all the wire harnesses and could get it to change RPM a few times up & down so i think it's a problem with my C101 connector and/or the engine harness.  i'm going to junkyard up a new harness & remove the connector this weekend.

maybe a bad connection or shorted wire is causing a false TPS signal to the ECU?

oh what fun....

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#31 06-21-2011 09:29:36

keith
Helper
Registered: 10-05-2008
Posts: 22

Re: my idle issue

Wooohoo!

"maybe a bad connection or shorted wire is causing a false TPS signal to
the ECU?"

I had a similar diagnosis. Maybe for once we were right?! :-D

Question, the IAC fails open on the XJ since it idles while
disconnected? Good to know if true!

My wifes yota failed closed. It would start but required immediate
application
of skinny pedal to keep it running. F'n yota's!

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#32 06-21-2011 10:17:31

nala
Helper
Registered: 05-25-2011
Posts: 25

Re: my idle issue

bj wrote:

checked voltage at the TPS.  it's the same with engine running or not, 4.69 in and 3.83 out which is right at .8% so it's correct.
.


While the supply voltage 4.69 is low; the out going voltage 3.83 is very high at idle...
Generally the supply voltage should be around 5.0 VDC and the idle voltage should be around .5VDC.
As for the low supply voltage.... I would disassemble the C101 connector, thoroughly clean the connector pins and receptacles with electrical contact cleaner and a small wire brush then apply some dielectric grease to stop further corrosion.
The high idle voltage indicates corrosion inside the TPS on the contact surface.... The TPS cannot be disassembled; but you can try to spray electrical contact cleaner into the TPS (while power is removed) and cycle the TPS. This my clean the oxidized contacts.
IF not.... Its time to replace the TPS.

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#33 06-21-2011 10:21:20

bj
Rookie
Registered: 05-18-2009
Posts: 88

Re: my idle issue

i was measuring it at the TPS using the ground lead from the TPS.  if i ground to the chassis i get 5.5v to the TPS.

i may have misread the procedure i found on the net.  i thought that output voltage should be .8% of the input voltage to the TPS at idle?

i guess if the output voltage to the ECU should be no more than .5v than my ECU may be fried?

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#34 06-21-2011 10:24:24

bj
Rookie
Registered: 05-18-2009
Posts: 88

Re: my idle issue

i was going from memory, and we all know what the first (or second?) thing to go is....

i knew that on my 5.0 ECU that .5v was max, i guess i should have known better with the XJ ECU.....d'oh.

stupid computers.  take this 3.83v and like it!  baaahh!

new TPS will be installed tonight.

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#35 06-21-2011 10:29:27

kram
Rookie
Registered: 05-24-2009
Posts: 95

Re: my idle issue

The older ODB0 Honda's have a mesh screen in the IAC passage. Mine
started dying pulling up to lights before it was completely warmed up.
Pulled the IAC and that screen looked like one of my arteries, 90%
clogged. :) Cleaned it with some of that "spares protective surfaces"
mass air cleaner and it's fine. I'm thinking of doing a new O2 sensor
on the car (1 wire), as mileage is starting to drop. I only got 28mpg
off the last tank, of course getting 32+ requires driving like a grandma
and that takes all the fun out of it.

Oh, the 5.0 has 5 volts on the tps, you can make those adjustable by
elongating the holes. There's a bunch of little tweaks you can do on
those to make more power.

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#36 06-21-2011 10:29:46

bj
Rookie
Registered: 05-18-2009
Posts: 88

Re: my idle issue

maybe i need to find a good mechanic.

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#37 06-21-2011 10:38:06

nala
Helper
Registered: 05-25-2011
Posts: 25

Re: my idle issue

Measuring to ground and reading 5.5V vs reading the connectors ground at 4.6V tells me you have some oxidized connections...
At 4.6V 8% would be .368V and at 5.5V 8% would be .44V. So my explanation of .5V is a recommended reading....
This voltage is being sent back to the ECU.
Doubt that your ECU is fried... It is just not getting the signals is it supposed to due to the oxidized connections...
Clean the C101 connector and your problems should be solved...

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#38 06-21-2011 10:38:39

kram
Rookie
Registered: 05-24-2009
Posts: 95

Re: my idle issue

.5-.7 volt drop across a forward biased PN junction. Everyone knows
that. The ECU might be floating or not at the same ground as the
chassis. .5 volt either way is probably within specs, when was the
last time the meter was calibrated? Is it a good meter? Yes clean the
connectors, check the engine ground, check the chassis ground. A
missing ground wire can cause weird stuff.

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#39 06-21-2011 12:12:55

big
Rookie
Registered: 09-27-2008
Posts: 55

Re: my idle issue

I'm gonna try that on mine! I remember inside where the TPS goes was kinda carboned up. Sprayed carb cleaner in it, but didn't fix my problem.

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#40 06-21-2011 12:15:22

bj
Rookie
Registered: 05-18-2009
Posts: 88

Re: my idle issue

I read on Naxblah that the "ground" wire of the TPS loom was NOT in-fact a direct ground?  I'm not sure where it originates from though, the ECU I guess?  Maybe I have a bad ground on the ECU?  I'm not even sure where that ground is....

So the proper TPS output signal should be 8% of input voltage?  I guess I thought it was 80%.

I'll try the new TPS and check out my ground at the ECU tonight.  Can't change the harness & C101 until the weekend.

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#41 06-21-2011 12:21:04

kram
Rookie
Registered: 05-24-2009
Posts: 95

Re: my idle issue

There is usually 3 wires on the tps. One is ground, one is Vcc, or B+
or your positive voltage, and then the 3rd one will change voltage as
the throttle is opened/closed. The TPS is just a potentiometer.

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#42 06-21-2011 12:35:40

bj
Rookie
Registered: 05-18-2009
Posts: 88

Re: my idle issue

sorry, but i dont agree with that at all.  nothing i've ever read about adjust the TPS says that you should have B+ (~12v) at the TPS.

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#43 06-21-2011 12:36:04

kram
Rookie
Registered: 05-24-2009
Posts: 95

Re: my idle issue

B+ is the voltage for that circuit. In this case B+ = 5vdc.

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#44 06-21-2011 12:36:29

bj
Rookie
Registered: 05-18-2009
Posts: 88

Re: my idle issue

i think maybe this is my fault for not specifying mine is an AUTOMATIC.  because the TPS adjustment is different for a manual.  so this says my numbers are RIGHT IN SPEC.  time to drop the TPS as a problem child and i will focus on the harness and ground loops at the ECU and engine harness.

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#45 06-21-2011 12:38:19

bj
Rookie
Registered: 05-18-2009
Posts: 88

Re: my idle issue

does anyone know what PIN on the ECU is the signal return from the TPS?  or have an ECU pinout diagram?

'88 4.0, auto

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#46 06-21-2011 14:05:46

stellarxj
Rookie
Registered: 10-05-2008
Posts: 73

Re: my idle issue

The maximum voltage you will probably see while the ignition is on; would be 90-95% of the input voltage during WOT.
There are several grounds in the engine bay and probably one or two near the ECU.
Didn't realize that you had a automatic....
Inst there a transmission module behind a kick panel that receives a signal from the TPS? Might check some of the connections there too!

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#47 06-21-2011 14:52:34

kev
Enthusiast
Registered: 09-27-2008
Posts: 102

Re: my idle issue

Yea, here:

See attachment.

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