Idle help please

supernoob · Post by **supernoob** » Wed Jan 25, 2006 9:39 pm

I've got a 90 Leg and I've got an idle that surges up and down, usually dying when going down. It was like that when I bought the car. I've tried replacing the following to no avail: MAF, IAC, Crank and Cam sensors, Coolant temp sensor, Alternator, Battery, Knock sensor, ECU. Whatever is causing it not to idle, is also causing the left radiator fan to cycle on and off and the same frequency as the idle surge when the car dies and the ignition still on. I thought for sure it would be the coolant sensor, but it wasn't. Any help is appreciated. Thanks.

Stephen

vrg3 · Post by **vrg3** » Wed Jan 25, 2006 9:51 pm

Is the air conditioning compressor cycling on and off at that same frequency too?

Have you tried looking for vacuum leaks?

supernoob · Post by **supernoob** » Wed Jan 25, 2006 10:29 pm

[quote="vrg3"]Is the air conditioning compressor cycling on and off at that same frequency too?

Have you tried looking for vacuum leaks?[/quote]

I didn't notice the A/C comp come on, but it may not even work anyway.

I was unable to locate any vac leaks.

I should also note that the motor has 207K, has MT and runs pretty decent other than the idle issue. It doesn't throw any codes and I've tried 3 dif MAFs.

vrg3 · Post by **vrg3** » Wed Jan 25, 2006 10:30 pm

Can you run my scantool to watch for funny stuff going on?

supernoob · Post by **supernoob** » Wed Jan 25, 2006 10:56 pm

Unfortunately, I don't have a laptop so that's not something that I could rig up anytime soon. And the car won't idle at all. What about the mechanical portion of the IAC valve? I just swapped out the electronic part of it.

vrg3 · Post by **vrg3** » Thu Jan 26, 2006 12:50 am

Ohhh... That could be part of the problem in itself. The relative position of the solenoid in the body is calibrated at the factory, and it's possible that you installed it in a position that's different enough that the ECU can't compensate.

dzx · Post by **dzx** » Thu Jan 26, 2006 12:59 am

So installing the top cream colored part in a different position could cause a bad idle?

Sixpack Subaru · Post by **Sixpack Subaru** » Thu Jan 26, 2006 1:54 am

Hey ppl, (I'm normally@NASIOC but I've heard plenty about this place...

When you swap the ISC, you should swap the whole thing, (I didn't even know the ISC was available seperately

, and in 15 years of working on them I never adjusted or dismantled any of them, (All the FSM's I ever read said it was not servicable/adjustable), but hey, that's in Australia

.
Most ISC issues can be sorted out by removing the unit, turning it on 'it's back' and filling it with carby-clean, (or SA459-Subaru Upper Engine Cleaner over here), or simillar. It is best to remove it when the engine is HOT, I know it's a bit nasty when the coolant lines are on there etc, (but I clamp those off with fuel line pliers anyway:D), but it comes up ALOT cleaner if the carbon/grime is hot when you spray it!), leaving it overnight can help in extreme cases also...
Hope this Helps
Cheers
Sixpack Subaru

vrg3 · Post by **vrg3** » Thu Jan 26, 2006 4:42 am

Dan - Yes.

Sixpack Subaru - They're not available separately, but they can be removed and swapped, even though you're not supposed to.

dzx · Post by **dzx** » Thu Jan 26, 2006 5:15 am

So should you be able to calibrate this by twisting it?

vrg3 · Post by **vrg3** » Thu Jan 26, 2006 6:25 am

By twisting it exactly the correct amount.

dzx · Post by **dzx** » Thu Jan 26, 2006 7:01 am

wow that sucks. That's probably what happened to my idle. Good thing the IAC will soon be unnecessary.

Sixpack Subaru · Post by **Sixpack Subaru** » Thu Jan 26, 2006 8:30 am

I have never heard of anyone swapping the 'motor' part of the unit....
Probably because it's 'very hard' to get it right once you have moved it?
I don't have a concrete spec for this situation. The ISC position is determined by the ECU but is based on MANY inputs...

Sixpack

supernoob · Post by **supernoob** » Thu Jan 26, 2006 4:38 pm

[quote="vrg3"]Ohhh... That could be part of the problem in itself. The relative position of the solenoid in the body is calibrated at the factory, and it's possible that you installed it in a position that's different enough that the ECU can't compensate.[/quote]

Swapping the top of the IAC was one of the last things I tried, and it didn't make the car run any differently. I'm wondering if there isn't a pinched wire somewhere in the engine wiring harness. That'll be the next thing to come off the old motor. Thanks for all the input. Keep it coming.

Stephen

Post by **Legacy777** » Thu Jan 26, 2006 5:32 pm

http://bbs.legacycentral.org/viewtopic. ... 458#151458

I swapped just the electrical part and tweaked it until the ISC duty % was in the middle of the specified range.

It's been ok, however it still isn't perfect. I would attribute that to the age of the electrical part I swapped onto the current valve.

vrg3 · Post by **vrg3** » Thu Jan 26, 2006 5:39 pm

Old motor? Did you replace your engine?

Oh, have you tried unplugging the oxygen sensor?

Post by **Legacy777** » Thu Jan 26, 2006 5:42 pm

Vikash, are you talking to me?

Old motor in being the old n/a motor.

No I haven't tried unplugging the O2 sensor. Why would that do anything?

vrg3 · Post by **vrg3** » Thu Jan 26, 2006 5:43 pm

Oh, sorry, no, I was talking to Stephen.

supernoob · Post by **supernoob** » Thu Jan 26, 2006 7:25 pm

[quote="vrg3"]Old motor? Did you replace your engine?

Oh, have you tried unplugging the oxygen sensor?[/quote]

Yes, this engine was in a different car before, with the same symptoms. Actually, it would usually idle in the previous car(with the same deliberate bouce), but now it won't idle at all.

I did try it without the o2 sensor. I wonder if engine grounding could be an issure. It seems like my other Leg has more in the way of ground wires.

scottzg · Post by **scottzg** » Fri Jan 27, 2006 7:40 am

Hey, i've run into this myself, and a couple gallons of toluene fixed it. Hah. Try some fuel injector cleaner.

supernoob · Post by **supernoob** » Mon Jan 30, 2006 3:14 am

Well, we finally might be onto something. I swapped out the wiring harness for the motor to apparently no avail. So I sent my friend to the parts store for some new plugs and some starting fluid to check for vac leaks. When he gets back, he says that it is starting to idle correctly ,but intermittently. Better than nothing. So we go on and swap the plugs and wires. Didn't help, not that we really expected it to. So then I start carefully listening to the clicking sound that turns the rad fan on and off in a cycle after the idle dies out. It was coming from the idle switch with the blue connector down below the pass side intake runners. It has a brown body with two vac hoses. So we swapped it out and it didn't seem to do anything. But then my friend left in the car and called me telling me that it starting to idle correctly and has thrown a 42 CEL- idle switch. There weren't any codes before, so I'm assuming it is reading a different signal than before, which hopefully is the right one. I told him to disconnect the battery overnight and see what happens in the morning.

Stephen

vrg3 · Post by **vrg3** » Mon Jan 30, 2006 3:36 am

That device is not the idle switch; it is the purge control solenoid.

The idle switch is built into the throttle position sensor.

Sixpack Subaru · Post by **Sixpack Subaru** » Mon Jan 30, 2006 8:46 am

supernoob wrote:Well, we finally might be onto something. I swapped out the wiring harness for the motor to apparently no avail. So I sent my friend to the parts store for some new plugs and some starting fluid to check for vac leaks. When he gets back, he says that it is starting to idle correctly ,but intermittently. Better than nothing. So we go on and swap the plugs and wires. Didn't help, not that we really expected it to. So then I start carefully listening to the clicking sound that turns the rad fan on and off in a cycle after the idle dies out. It was coming from the idle switch with the blue connector down below the pass side intake runners. It has a brown body with two vac hoses. So we swapped it out and it didn't seem to do anything. But then my friend left in the car and called me telling me that it starting to idle correctly and has thrown a 42 CEL- idle switch. There weren't any codes before, so I'm assuming it is reading a different signal than before, which hopefully is the right one. I told him to disconnect the battery overnight and see what happens in the morning.

Stephen

Cool...
When the Purge solenoid, (canister purge valve), fails it normally fails 'open', (I have NEVER seen one fail closed:D ). It creates a lean condition, the Injectors open for longer, (more fuel is added), raising the idle, then the ECU tries to close down the ISC..etc etc.
Basically, the purge solenoid can throw a few codes when it fails...Knock sensor is the most common, then Oxy sensor, and sometimes MAP sensor too....etc etc.

They are VERY common for failure over here, I just assumed it would be all different over there...:d Everything else is

If there is an idle switch fault, back off the TPS until the signal voltage to the ECU is around 0.5Volt, then (with the engine off but ign on of course!), Go to full throttle, (WOT), and see if the voltage increases from 0.5Volts when closed, to 4.5-5.0Volts when fully open.
Hope this helps

Cheers

Sixpack

free5ty1e · Post by **free5ty1e** » Mon Jan 30, 2006 2:51 pm

Whoa. Your toilets flush backwards, AND your throttle position sensors operate backwards. Australia sure is a strange place

My TPS reads ~4.5v at idle, and ~0.8v at WOT.

vrg3 · Post by **vrg3** » Mon Jan 30, 2006 4:22 pm

No, Chris, theirs read the same way as ours. Sixpack must be thinking of later models. Our later models also read the opposite direction.

I've seen several purge control solenoids fail "closed." They don't actually seize shut, but rather develop cracks in the solenoid wiring so the solenoid stops functioning.

Stephen, if you want to check your idle switch, search for posts by Josh about it; there's a much more precise method for calibrating it. Following this procedure may resolve your problem. Or if your throttle body has been tampered with, maybe you should try swapping to a known-good throttle body with calibrated TPS already installed.

In my experience the ECU will trip the idle switch code sometimes when odd voltages or loads are seen at any of the TPS lines.

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Idle help please

Idle help please