Sometimes high idle, goes away after restart

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Beretta1234567
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Sometimes high idle, goes away after restart

Postby Beretta1234567 » Wed Feb 18, 2015 10:01 am

96 Beretta 3100 v6 and auto.

Only on a cold start, and only when its extremely cold outside this happens, car idles high.
Last edited by Beretta1234567 on Thu Apr 21, 2016 3:02 pm, edited 1 time in total.



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Re: Sometimes high idle, goes away after restart

Postby Asylum » Wed Feb 18, 2015 11:07 am

I think you are on the right track.

They get old, lazy and tired after a while (kind of like me, LOL!) especially on vehicles that don't get driven a lot.

My Quad actually throws a code once in a while for the same thing, and wants to idle a little high for a bit, but it goes away after it warms up.

Let us know. :beer:


Eric

Asylum Motorsports
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'92 3500 GT gone and not really missed. It was fun. Documented 13.47 N/A.

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Re: Sometimes high idle, goes away after restart

Postby ifixalot » Wed Feb 18, 2015 12:19 pm

Never had idle creep up like you describe.

On my 3.8 mini van, high idle was caused by a bad TPS. Actually coolant got into it.

I think too, if a temp senor is bad or has bad connection it might make the ECM
think the engine is colder than it is. It takes more throttle to idle a cold engine with thick oil.

In the daughter's 90, the ECM pins were corroded and caused the IAC to remain open
causing high idle.

And on a 3.8 Turbo Regal, the butterfly was loose from the shaft so it had play between it and the return spring.
So the idle was intermittently high on that car.

Just some things to check out.



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Re: Sometimes high idle, goes away after restart

Postby Money pit Beretta » Wed Feb 18, 2015 7:31 pm

Don't forget to clean out the port. Feeling like the IAC is worn out and do to the cold everything is tight. If the poor worn out thing is fighting near frozen gunk that would slow it down too.


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Re: Sometimes high idle, goes away after restart

Postby yellow3800 » Sat Feb 21, 2015 11:49 pm

do the above things too. Good ideas.
That ecm corrosion will sneek up on yah. If so, drain all power, batt off and key on to be sure. Then take toothbrush/metalbrush and scrub corrosion out of the connector with a parts cleaner. Elec contact is best, cyclo makes it. Do same to computer pins. Do not use vinegar or any acid... It will wick into places and cause more harm than good. When all corrosion powder and evidence gone, pack it with di electric grease and re assemble! You may not need to replace anything... Except the leak cause problem.

Otherwise id try:

Kiss principle - manually move the throttle on the intake by hand to the idle stop to eliminate throttle creep during this cold start. Suspect aging cable tightens and shortens from cold. Vibration draws idle up until local area is heat soaked before it backs down. Its probably more the cable interface or cable bends from age rather than internal chafing. When i saw cars do this, they barely made it to 2krpm. You may have a muli layered problem! My favorite!

If idle stop is hit and idle increases, we know its not the cable system.

I hav seen active egr systems gunk up the intake area causing turbulent airflow around the iac valve. Not likely here, but itmay help you think more.

Fuel pres regulator shouldnt allow a continuing change if its theculprit and bypassed. Itd be nice to verify pressure later as this issue escalates... Not now. Its unlikely.

Moving to electrical... Wiggle check. Start at iac andfocus on wires near exhaust... They will corrode faster if moisture soaked with added heat and will cause all kinds of fluctuations that the computer wont know what to do since they stay inside limits.
I know those hard plastic conduits may break... Dont be that rough. Im focused on 18" from the iac and tps, which is little conduit. Move slowly.

If it does change, pull out wires from conduit individually and positive corrodes first, all things equal. Grounds go at grounding points.

If the new sensor changes nothing, verify grounds with multimeter, tps and iac first. If no meter, id use an alligator clip to get it to the shock tower or battery since its close by. I break the insullation with a pin and cliop onto that. When done, cover the pinhole with di electric grease, rub it in.

I had a car years ago that had a similar problem and it was a gnd wire going in and out... Funny thing was that i got good at ignition cycling while driving to reset it during the 5mo of troubleshooting. The key on/off cycle seemed to reset the ground for 20min... Weird.

Its midnight. Im out of good brainwaves.

Break a leg!

Andy



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Re: Sometimes high idle, goes away after restart

Postby Rettax3 » Tue Feb 24, 2015 12:03 am

IAC sticking due to cold is most likely, as stated. I recently worked on a Toyota that had a similar issue (although it never dropped RPM like yours once warm), caused by corrosion inside the IAC valve.

A bad IAT sensor/MAF issue is the next most likely, coupled with an O2 sensor problem (especially the heater circuit) maybe. Can you read any data-stream from the car? Some of the auto parts stores have scan-tools as code-readers that are actually capable of reading live data, albeit slowly. The local O'Reilly's had that ability until some jack-wagon walked off with their tool, now the store manager won't replace it with anything but a basic code-reader. :no: I've sent a customer there for a scan when I couldn't get to her car, only to find out that their new 'tool' isn't even capable of reading OBD1 ECUs... :fool: Wow.

Of course, since your problem cures itself once warm, you may not actually see the problem at the store, even if you can access such a scan-tool...

Edit: Andy, it is good to see you so active on the board right now... I hope you keep sticking around. :friends:


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Re: Sometimes high idle, goes away after restart

Postby Beretta1234567 » Sat Feb 28, 2015 8:50 am

I replaced the IAC and cleaned out the throttle body.
Checked throttle, cable is fine, does not open as you explained it could have.
Its temp gauge did not do much, it only went from about 2mm below cold to about 0.5 mm below cold in this span of time.
still revs up.
Last edited by Beretta1234567 on Thu Apr 21, 2016 3:03 pm, edited 1 time in total.



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Re: Sometimes high idle, goes away after restart

Postby ifixalot » Sat Feb 28, 2015 11:24 am

Air has to be getting into the engine somehow for it to idle high.
How is the PCV valve? Maybe crud or ice inside?



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Re: Sometimes high idle, goes away after restart

Postby Money pit Beretta » Sat Feb 28, 2015 12:36 pm

Bad TPS or as said an air leak. Also check the TPS wires at the pig tail.


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Re: Sometimes high idle, goes away after restart

Postby Beretta1234567 » Sat Feb 28, 2015 4:35 pm

Wouldn't an air leak stay instead of going away when warming up?
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Re: Sometimes high idle, goes away after restart

Postby Money pit Beretta » Sun Mar 01, 2015 10:25 am

Not if the computer adjusts to the "extra" air.


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Re: Sometimes high idle, goes away after restart

Postby ifixalot » Sun Mar 01, 2015 10:57 am

Check the PCV circuit, not only the valve but the pipe and the rubber components that connect it all together.
That fitting on top of the engine intake just behind the throttle body, is it sealed well?
The plastic pipe itself gets brittle and can crack.



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Re: Sometimes high idle, goes away after restart

Postby yellow3800 » Mon Mar 02, 2015 12:25 am

Oh, we are starting to have fun now!

I like the above suggestion on cracking of that plastic pcv line. It doesn't explain why a computer [key off] reset fixes the problem. this smells like electrical.

If this was a nissan, Id say unplug the one or two temp sensors. Forgive my ignorance on this, I don't know how many sensors we have. some gm cars have one that does it all [3wire] and some with two where one feeds the ecu, and the other goes to the gauge. in nissans, and probably others, this default [open in temp circuit] causes the car to idle high, but it will do it again if started again. last time I checked, our cars don't care about this; which makes sense because a clutch fan cools the motor better at the higher idle, and thats why they design theirs this way. It actually doesn't cool better - it serves as an alert that the temp system is defaulted.

If the car were in front of me, in my bedroom as I type this, lol, I'd unplug the sensors and see what default loop does. tps, first probably, by itself, then iac, by itself. It really hurts to see this happen only on the first startup. HOW ANNOYING! its like a double-intermittent level! I think that if the tps is unplugged, it will run with pedal pressure needed, or risk not idling, then the iac will overpower it, and we will know if its not doing the same thing, we may know why.
taking apart a tps and cleaning the carbon tracks with electrical cleaner [cyclo makes it, good stuff] clears the dust from muddying the signal as the position on the tracks needs a narrow tolerance. maybe a good cool down leaves this dust to settle and messes up the first start. Makes me think to put the key on and cycle the gas pedal to the floor several times before start. I'm not sure if it will do anything. pwr will visit the tps, so its worth a try in my book. You can tell I don't like replacing anything until its broken! buying an alternator plays with my psyche because the case, bearing, and field do not need replacing! but the whole thing is cheaper.

I want to fool the car into thinking its 2nd start of normalcy actually occurs as the engine runs for the first time. this way, when we fool the system, we know what system.

I rarely see sensors bad. Yes, I know they go bad. I'm just stating that the systems of communication are more fickle than the sensors themselves. This reminds me of a light bulb going out, sometimes the filament is broken just enough that when we tap the bulb, it illuminates and temporarily 'welds' itself via electromagnetic force; the broken filament as long as its on. when cold[off], it relaxes itself and won't turn on again until bumped and then will stay lit indefinitely.

could the tps be doing this?

this sounds like a ground failing [like the lightbulb idea], just barely enough that it freaks out the car, and a reset surges what little power is needed to repair it for the 2nd start.

makes me wonder if you key on and key off, then [on] and start if it will simulate the first engine start. I'd try this too. does any number of key cycling simulate this first 'high-rev' startup?

If this idea is way off track, and doesn't trip up the car's problem, I'd pull out the multi meter and check gnds of tps and iac. on the harness side ...while its wiggle checked. Its always a good idea to find the ground intersection in the harness and visually inspect it for corrosion. while rare, it does happen, and often not electrically as much as oxidation after heat and your Michigan-like cold temps in the morning shrink the insulation back and it hardens and stays pulled back. oxygen attacks copper and we see green and powder thereby setting up an infamous 100ohm ground. I would only visually check these gnds if the ground measurement readings are anything more than 0ohms. ...remember to zero the scale or know what the test leads read when crossed to get a 'zero' figure.

* A fun way to still avoid the book, is to keep the multimeter on VOLTS and probe the connector. That way, you can put wires whereever you want to, and it won't blow the fuse. There are 3 pins on the tps and iac I think. unplug one. with 3 pins staring at us, put the red or black wire on the neg post of the battery. probe all 3, with key on, and look for voltage. the pin[s] that give voltage are NOT grounds. if there is one, we eliminated one. now the other two, if there are two, turn the key off, red meter wire goes on positive on battery, and then prob the connector pins. only one should measure +12v. the one that does, is gnd. Now switch the meter to ohms scale, probably 200, not 200k, 20k, etc. put the negative on the negative of the battery and the other multi meter [red] wire on the pin we found to be ground. The meter should zero, or if digital, read the same when you touch both red and black wires OF THE METER. wiggle the wires and see if you can fluctuate the meter reading.

If this does not read zero, and or fails the wiggle check, we hunt the wire for the bad spot, or just shotgun a new one in to that ground junction after putting an alligator clip on the gnd wire and running it to gnd to verify that we need another gnd wire. AND I'll have to get out the book and ensure that the gnd wire is supposed to be a full gnd. I think all wires in these two circuits may go direct to the computer. If they do, it may not give a full gnd at 0 ohms. It also may give a 0 ohm gnd. This is almost not worth mentioning because I think the problem is elsewhere. I just mention it because I haven't opened the book yet.

If it does read zero and passes the wiggle check, [tps and iac] I'll have to pick a different tree to bark up. the positive sides of the wires are probably good because the ecu regulates them and the problem goes away. bad positives often reveal themselves in a wiggle check, not in the ecu box.

sorry for getting excited at your expense and typing a small book. I like these kinda problems because of the sense of accomplishment when we win! Another psychological flaw, I know, lol.

Andy
89gt--->with cleaned tps 30k miles ago.



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Re: Sometimes high idle, goes away after restart

Postby Beretta1234567 » Mon Mar 02, 2015 9:34 am

I have not had time to check anything else at the moment.
Last edited by Beretta1234567 on Thu Apr 21, 2016 3:04 pm, edited 1 time in total.



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Re: Sometimes high idle, goes away after restart

Postby ifixalot » Mon Mar 02, 2015 10:17 am

""I like the above suggestion on cracking of that plastic pcv line.
It doesn't explain why a computer [key off] reset fixes the problem. ""
I didn't take time, to speculate as to why a cracked PCV tube may stop effecting a high idle
when you restart the car. Weird stuff happens when computers are involved and sometimes the
explanation comes after the problem is unveiled.
I look for simple defects first.
I know that on my 96 Z26, I have had the rubber elbow to the PCV valve rot and allow extra air
into the engine. Mine was easy to find because it whistled.
I also have had to make a new grommet where the tube goes into the engine intake.
Which also caused an erratic idle speed due to it's sloppy fit.
On my daughters 96 the plastic tube was cracked on the intake side of the crankcase.
So I threw that in there thinking maybe his tube has a crack.




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