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Idle+Lights ... again

bigalpha

bigalpha

Moderator
Location
Tucson, AZ
A while back I had crazy idle issues and issues with my blinkers in my 1988 MJ.

During my initial troubleshooting, I did a few things. After I replaced the bulb sockets and headlight switch, the blinkers returned to normal. After I replaced the ground wire on the TPS, the idle dropped down to almost normal.

Both issues have cropped up again. First, I would get the left blinker indicator lighting up as I was driving, then it would go away. Then, the blinker indicator stayed on. Now, both indicators are staying lit up and the blinkers don't work as they should.

The high idle is back, but it's not quite as high as it was before. It happened in stages, too. Every once in a while I would start the truck and it would idle really high in every gear. I could turn off and restart the truck and the idle would be normal. Well, it's stuck at freakishly high idle again and no amount of restarting will help it.

I don't know what to do at this point. I don't know whether it's an electrical issue -- a bad connector somewhere. Or a poltergeist.
 
I just so happen to still have my 88 FSM open to the right diagram from trying to help stevenspann yesterday... Looks like you should put an analog multimeter set to the 10 or 20 volt scale on pin C7 of your ECU, a yellow/green wire. Check voltage at idle (0.8 volts is the good value I think?), then move it slowly and carefully and watch for the needle to jump around. If it doesn't jump around I think the TPS is fine and you should check elsewhere (intake leaks, vacuum leaks especially on the brake booster line, etc etc.) I'm no Renix expert though, so I could be completely wrong here.
 
Well, I would start with cleaning all battery cables and renewing all grounds. There should be three ground wires at the dipstick tube--ICM, ECU, and o2 sensor, all critical.

Pay particular attention to the ground strap at the rear of the head to the firewall. Those strap degrade, and without a good unibody ground all sorts of weird electrical issues will crop up. I would replace the strap with a cable.

Once you get that done post back.
 
I have a 5-90 ground cable from batt to block and those grounds have been cleaned. Strap ground at firewall has also been cleaned.

Tested against the battery, the ground cables all register less than 5 ohms.
 
Ok.

High idle is a lean condition, so use an unlit propane torch to check the entire vacuum harness, both front and rear sections. Test the MAT sensor, if it is shorted to ground it will cause a lean condition.

You have of course already cleaned the IAC and throttle body. Tried unplugging the IAC when you have the high idle? What was the result?
 
New bulbs, new bulb sockets, ground is good (tested against battery).

When I turn on the parking or headlights, the indicator lights up and blinker does not work.

With no lights activated, teh blinker works just fine.
 
Sounds like a bad ground.
 
joe_peters said:
Ok.

High idle is a lean condition, so use an unlit propane torch to check the entire vacuum harness, both front and rear sections. Test the MAT sensor, if it is shorted to ground it will cause a lean condition.

You have of course already cleaned the IAC and throttle body. Tried unplugging the IAC when you have the high idle? What was the result?
Click to expand...

When I say high idle, I mean really high. Not like 1000RPM, but so high that when I shift from P to D it peels out.
 
joe_peters said:
Sounds like a bad ground.
Click to expand...

or burnt head light switch.

i would pull the head light switch and look for burnt wires/terminals. renix electronics are known for burnt headlight switches(im in the process of rewiring my fuseblock and also have had a burnt headlight switch)
 
89xj said:
or burnt head light switch.

i would pull the head light switch and look for burnt wires/terminals. renix electronics are known for burnt headlight switches(im in the process of rewiring my fuseblock and also have had a burnt headlight switch)
Click to expand...

Switch is brand new. When I replaced it, I inspected the wiring under teh dash and it's all A-OK.
 
I had the exact same light problem to a T. The ground showed ok at the wire pigtail but it wasn't making it into the bulb socket. I didn't feel like replacing the socket so I jammed a chunk of wire into the socket and grounded that. Voila, turn signal.
 
with electrical problems you have when you turn on the headlight switch, check the grounds and if grounds are all good, then check for a short.

high idle may be from a bad gound to the tps or to the ecu side of the tps.
 
I'm going to check the bulb sockets again and make sure the grounds are still good. They worked perfect when I replaced them but maybe something weird happened.

The TPS connector has a bad ground, so I spliced in a new ground straight to battery. That solved my initial blistering idle. But, the ground is still good, so maybe the sensor is bad somehow.
 
bigalpha said:
I'm going to check the bulb sockets again and make sure the grounds are still good. They worked perfect when I replaced them but maybe something weird happened.

The TPS connector has a bad ground, so I spliced in a new ground straight to battery. That solved my initial blistering idle. But, the ground is still good, so maybe the sensor is bad somehow.
Click to expand...

i would have to look at the renix fuel injection maunual for the pin numbers, but have you checked the ground pins on the ecu?
 
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