intermittent surging idle

[black89t]

hey so i have this intermittent surging idle problem since last saturday. right before i was about ready to line up and race at the local street legal drags. this is in my truck with a 7mgte swap. truck had been running great then out of know where i have this surging idle from roughly 1000-2000rpm. ended up running a high 15 at 93mph because i couldn't hold the rev's steady at the tree. and i was loosing tons of boost too. so i figured out that the iscv is the problem. i swapped a known good iscv and it still randomly surges. so something is not contolling the iscv right. i checked my tps and it was in spec. im about ready to try a different ecu. so my question is basically what inputs determine what the iscv does? what are the most likely causes you have run across?


the street legals are tomorrow and i need to get this beast down the track running tits!!!! so lets here what you guys think.

 

[hvyman]

Ecu's rarely go bad. I think i heard of one and it was user error.

Id look more at the wiring and clean the valve. You have the little orange flappy thing in right? With the metal on the outside so boost doesnt blow the valve open.

 

[black89t]

Ecu's rarely go bad. I think i heard of one and it was user error.

Id look more at the wiring and clean the valve. You have the little orange flappy thing in right? With the metal on the outside so boost doesnt blow the valve open.

the check valve is in. im gonna look more into the wiring tomorrow morning. just was hoping somebody had a similar problem....

 

[hvyman]

Have you checked your codes?

 

[Scruggs86.5T]

I had this issue a little while back idle between 1-2k constantly going up and then down like the ecu is constantly trying to recorrect for something that it isnt seeing, although mine wasn't intermentent. I dont really know what you mean by that, like this is happening at random times or the idle is intermentent. Well in my case this meant that there is a vaccum leak on the engine side of the throttle body, meaning in between your plenum and TB, between the upper and lower runners, or between lower runners and the head. I guess it could be a leak say on the larger front vac. tube that goes the the vac. tree under the manifold or your rear that goes to the brake booster.
This explains the idle issue and loosing boost. Hopefully this is what it is and it is easy to get to. Mine was in between the upper and lower runners, at least it wasnt at the head, right? Well good luck with it, let us know what you find out.

 

[black89t]

Have you checked your codes?

no not yet. i haven't been able to get the check engine light to work. its lookin like im gonna have to do it through the diag port...

I had this issue a little while back idle between 1-2k constantly going up and then down like the ecu is constantly trying to recorrect for something that it isnt seeing, although mine wasn't intermentent. I dont really know what you mean by that, like this is happening at random times or the idle is intermentent. Well in my case this meant that there is a vaccum leak on the engine side of the throttle body, meaning in between your plenum and TB, between the upper and lower runners, or between lower runners and the head. I guess it could be a leak say on the larger front vac. tube that goes the the vac. tree under the manifold or your rear that goes to the brake booster.
This explains the idle issue and loosing boost. Hopefully this is what it is and it is easy to get to. Mine was in between the upper and lower runners, at least it wasnt at the head, right? Well good luck with it, let us know what you find out.

i meant intermittent as in it will be driving fine then i'll park and start it up. then it starts to rev up to 2000ish then down to 1000ish rpm. i'll drive it then usually it will stop surging. but of course last street legals when the problem started it wouldn't stop! :: angry ::

another thing to note is that it won't pull a good amount of vac on decel when this is happening also its causing a boost leak. i know the check valve should stop the boost from leaking if the iscv is the issue but i still am pointing my finger at it. then when it does go back to normal it pulls good vac, boost like it should, and idles just fine. :aigo:

oh and how i narrowed it down to the iscv is if i plug the hose that goes to the accordian hose for the iscv it will idle fine. its pulling a shit ton of air through that hose when the problem is going. its like thescv just stops actuating. still a little buzzed from last night though so lmk anymore details you might need.

 

[Scruggs86.5T]

Yeah, if it is intermentent like you explained it then it is not what mine was. Mine was all the time. Yours definately seems to be the ISCV. There is a procedure for checking the ISCV in the TSRM.
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=106
I would start there. Although the ISCV doesn't explain the boost loss, that could be a completely different problem altogether. If your ISCV is shot, I have one for sale in my FS thread on here, I am just down here in Petaluma depending on how bad you need it.

 

[jetjock]

...if i plug the hose that goes to the accordian hose for the iscv it will idle fine. ..

 

[black89t]

^are you implying i should just plug it and say screw the iscv jetjock? because thats what i did yesterday. totally cured the problem. even though its hoaky fix. truck idles fine and pulls consistant. ran it at the drags and found that it hooks up better on the street that the dam track! :aigo:

it was spin city. that open diff is killing me. it takes to much time and distance before i hook to run a good time and trap a good speed. it didn't start to pull hard until 3rd. gonna have a locker in it by next one so it should solve my traction issue.

 

[ForcedTorque]

The ECU will cut fuel if your idle goes above 1700. So the problem could be something merely raising the idle, and the ECU correcting from there.

 

[black89t]

The ECU will cut fuel if your idle goes above 1700. So the problem could be something merely raising the idle, and the ECU correcting from there.

hmm........thats a nice piece of info. well i know the idle is being raised by the air its pulling through the iscv hose. im gonna start looking into the wiring for the iscv. the way it just runs great then bad leads me to believe the iscv somehow isn't getting a signal.

 

[jetjock]

..are you implying i should just plug it and say screw the iscv jetjock?...

No. I was pointing out that plugging the hose and having the engine do what it does should be telling you something but so far all I see is more faulty logic...

 

[black89t]

No. I was pointing out that plugging the hose and having the engine do what it does should be telling you something but so far all I see is more faulty logic...

well whats wrong with my logic? it would be nice if you could just help me. when im on here i don't withhold info from other members that i know will help them solve an issue.....isn't too nice. forcetorque is having a similar problem to so it would be very cool to have a thread that has a fix for this. im sure were not the only two either. to me it seems the iscv operates perfect when it does idle then when it acts up its like it just stop actuating. thats what leads me believe theres a intermittent open circuit to the iscv.

 

[Scruggs86.5T]

Keep in mind the ISCV is essentially a motor that spins a piece in and out to adjust the idle. Most likely when you are oscillating at idle your motor is fully open and allowing max air in. This is why it seemed like a large vaccum leak behind the throttle body. So either the ISCV isn't doing its job or there is a wiring issue of some sort. I would check the easier of the two being the ISCV per the TSRM. But the only problem with this is that it is intermetent, so the ISCV might act like it should or it could go fully open. Good luck with it.

 

[nothix]

Having this same problem. Did you ever find a solution?

 

[3p141592654]

I would check for a code 51.

 

[FVBP]

Did you find the problem? Mine started as a temperature related problem. If the outside temp was about 70 I would get rough running at 40 mph when I got three miles from home and then it would quite this would continue until the outside temp changed. So twice a year I would see this as the temp went through 70. This has been happening for three years. Then along comes fall and it started again, but this year it didn't quite. I got 3 miles from home and it started and I thought here we go again, another week of rough running for five minutes, but then it continued. I could fill it sort of stumbling. When I got to my detination, I put it into neutral to let the turbo cool down. Now for the first time, I can see it is Idling funny, it is cycling between 1000 and 1800. So on the way home I watch for this when it was going down a hill no load I could see and feel it follow the surging, and when I came to a stop it was idling high at 1100 instead of 700. Got out my manuel out and it says nothing about surging. So I need to study and see if I can figure out which temp sensor would control the fuel system. The ISCV looks like sensor of valve position.

 

[FVBP]

Did you find the problem? Mine started as a temperature related problem. If the outside temp was about 70 I would get rough running at 40 mph when I got three miles from home and then it would quite this would continue until the outside temp changed. So twice a year I would see this as the temp went through 70. This has been happening for three years. Then along comes fall and it started again, but this year it didn't quite. I got 3 miles from home and it started and I thought here we go again, another week of rough running for five minutes, but then it continued. I could fill it sort of stumbling. When I got to my detination, I put it into neutral to let the turbo cool down. Now for the first time, I can see it is Idling funny, it is cycling between 1000 and 1800. So on the way home I watch for this when it was going down a hill no load I could see and feel it follow the surging, and when I came to a stop it was idling high at 1100 instead of 700. Got out my manuel out and it says nothing about surging. So I need to study and see if I can figure out which temp sensor would control the fuel system. The ISCV looks like sensor of valve position.