will a bad ISC or ISC motor cause this?

[xlMcMlx DsM]

I have idle surge ion my 1990 TSi, but theres this, also. I try to hold the throttle open manually, to hold a steady rpm, and the revs go up and down a bunch, like regular idle surge. Can the ISC being bad cause this?

 

[xlMcMlx DsM]

I also looked at the VFAQ on idle surge, and i tried the test where you turn the key from ACC to ON a few times. It was really loud( could hear it from inside the car pretty clearly), but moved in and out fine. I finally got it off the TB after breaking(another) set of craftsman screw extractors. The tip was covered in black crap, so i wipped it off. But im getting a new one on tuesday, so ill see if that helps. but any other suggestions would help.

also, when i ohm tested it, none of the pins read over 30 ohms. On the VFAQ page, it says it should be at least 30ohms when the engine is cool, which is what mine was.

 

[steve]

when i ohm tested it, none of the pins read over 30 ohms. On the VFAQ page, it says it should be at least 30ohms when the engine is cool, which is what mine was.

The thing you worry about is when the resistance of a coils is below the spec. Anything below 10 ohms is risking burning up one of the drivers in the ECU from too much current.

Steve

 

[TwoLiterLaser]

Perhaps I was too general in my explanation. Michael Hamilton gives both a very good FAQ and explanation of what is going on at this site:

http://www.ecanfix.com/users/mdhamilton/ecuconversion.html

The Tach signal does indeed come from the coil and not the CAS.

 

[xlMcMlx DsM]

The thing you worry about is when the resistance of a coils is below the spec. Anything below 10 ohms is risking burning up one of the drivers in the ECU from too much current.

Steve

So does that mean my isc is fine? becuase im running out of options for my idle surge and surging under constant throttle. Im thinkin its a combination of boost leaks, and the isc.

 

[xlMcMlx DsM]

i was actually thinking that my surge could be because of the fuel system. The guy i bought it from had to put a new fuel pump in it. He said it was just one he got from autozone, so i assume its a stock one. But theres a lot of wires that were cut and re-soldered on the ecu which leads me to believe that the car had some type or fuel control or something like that. But im just gonna change the fuel filter, and rewire the fuel pump to be safe.

 

[xlMcMlx DsM]

gonna order that keydriver transistor and a new ISC also, and see if that helps. I just put in a new BISS and o-ring, and i pulled the FIAV plate off and put RTV on it to make sure it's sealed good. The EGR is blocked off also. And i found out i put the throttle plate in backwards oops. I put in the right way now, so it works better.

 

[LordZed]

gonna order that keydriver transistor and a new ISC also, and see if that helps. I just put in a new BISS and o-ring, and i pulled the FIAV plate off and put RTV on it to make sure it's sealed good. The EGR is blocked off also. And i found out i put the throttle plate in backwards oops. I put in the right way now, so it works better.

Bet the throttle plate being corrected helped a lot huh?

 

[xlMcMlx DsM]

i havent checked yet, but im sure it will. theres less of a gap in the TB from the throttle plate now. I ordered my new ISC($40) and it should be here this week, then we'll see if that does anything.

 

[spaceball]

if the surge condition in happening above 1/4 throttle the isc is not the problem. if the ecu can not see that the idle switch is off then the ecu will be trying to make the car idle by adjusting fuel trims and timing while you are trying to drive. then when you come to a stop the idle trim will be so far out of wack that it will continue to surge while it adjusts again.

 

[xlMcMlx DsM]

if the surge condition in happening above 1/4 throttle the isc is not the problem. if the ecu can not see that the idle switch is off then the ecu will be trying to make the car idle by adjusting fuel trims and timing while you are trying to drive. then when you come to a stop the idle trim will be so far out of wack that it will continue to surge while it adjusts again.

I switched the ECU pins 6 and 14, the idle control ones, because the ecu is a different year than my car. Doing that stopped the idle surge during warm up, but there was still idle surge after warm up. The throttle surge thing i think is a bad boost leak, or something to do with the fuel system.

also, im gonna go get a new idle swtich, i think that could be some of the problem.

 

[spaceball]

that's half the battle. now your looking at a dead or slow 02 sensor if it surges only when the car goen into closed loop. i cant garantee that its the o2 with out testing myself but that is the most likely suspect. if it checks out ok pull the wire off the ect and o2s, now the ecu should be in limp mode, drive it , if it runs like absolute shit(it may bog but it should not sputter or surge) you may have a bad maf. diag could me much less painful but im assuming you dont have access to a silly scope.

 

[xlMcMlx DsM]

i have access to a genisys scan tool at my high school. I can use that to see what codes it may throw, or check the sensors and what not. But ill test the 02 sensor, and see what comes up. I dont know the condition of it, so that could be part of the problem.

 

[xlMcMlx DsM]

i got my isc yeasterday, put the TB on the car today, and started her up. Oddly, the surge started just a minute or so after it was running. ?? i think i might just have a leak somewhere, because i threw it together really fast, so i'll check for that tomorrow. But im gonna pick up an idle switch, and order an 02 sensor when i get some money.

 

[xlMcMlx DsM]

also while i was reading the idle surge faq on VFAQ, it was saying to disconnect the idle switch and the "rpms should stabilize". Mine doesnt. it just keeps surging. Whats up with that?

 

[LordZed]

also while i was reading the idle surge faq on VFAQ, it was saying to disconnect the idle switch and the "rpms should stabilize". Mine doesnt. it just keeps surging. Whats up with that?

I've read that before too. Mine does not stabilize when I disconnect it. No leak's either. On that theory though. I don't know why disconnecting the isc WOULD stabilize the idle. Theoretical the isc would be in the same place as when it was connected right? So if it's got a step burnt out of it's cycle, it would just keep doing the same thing because the spindle is in the exact same place. But that's just a theory. My theories are often wrong though.

 

[steve]

while i was reading the idle surge faq on VFAQ, it was saying to disconnect the idle switch and the "rpms should stabilize".

The ECU is looking for the IPS to tell it that the throttle is closed before it does any of the checks that cause "idle surge". By disconnecting the IPS the ECU should never think the throttle is closed and not try and manage the idle speed. If yours is still surging you should hook it back up and check with the datalogger that the ECU sees the IPS working. You can test some of it using a volt meter. The ECU pulls the wire up to 12v and the IPS grounds it when the throttle is closed. So you shouls see 12v on the connector when the throttle is open and 0v when it closed. If you still have the rubber boot over the spade connector you will have to pull it back to make a connection with you meter while the wire is connected to the IPS.

A somewhat related problem is where the car won't idle becasue the IPS isn't making a good ground. That can be caused by a missing ground strap on the throttle body.

Steve

 

[xlMcMlx DsM]

mmm, ok i see. I can ground the TB to the firewall with some wire 10ga wire i have. Theres a screw hole on the top and i think thats what it might be for. Ill do that today, and check the voltage of the IPS. Thanks guys, this is really helpful. Ill update you today after school.

 

[xlMcMlx DsM]

ok, i tested the TPS, and i think its bad. My Haynes says it should read 3.5k-6.5k when closed. Mine was 3.6k. Then is tested the range of motion, and the manual says it should go from 1.1K to 5.6K, well i had to set mine at 1.1K, because it was off, but when i put it at WOT, it only went to 3.92K. which i figure means i need a new one.

 

[steve]

Please get a real manual, these aftermarket one cause more crap.

A 1G TPS can read anywhere from 3.5k to 6.5k from pin 1 to pin 4 (total resistance) according to the spec. They need to change resistance smoothly without any spikes or dropouts. When correctly adjusted the ECU should be receiving a 0.48v to 0.52v signal at idle with the throttle closed. What it reads at WOT depends on how much slack is in your throttle cables above what is specified. You should not adjust your TPS for a WOT reading, you set it to read correctly at idle and it reads what it reads at WOT.

Because both the sensor +5 voltage and the total TPS resistance vary from car to car you cannot set the TPS by resistance unless you measure the values on your car and do the math to come up with an output voltage of 0.5v at idle. Read up on voltage dividers to understand why.

Now why are you messing with the TPS? We were talking about the IPS, that switch on the back side of the TB.

Steve

 

[xlMcMlx DsM]

its just that i read up on some people whos idle problem was their TPS, so i figured it wouldnt hurt to check. Its adjusted correctly, reading what it should at idle, or with the throttle plate closed. Now back to the idle switch and what not, Is the connector supposed to be fairly loose? mine can be pulled off with little to no effort, and it wiggles a lot when conencted. Lately i havent done much to the Talon, because i just rebuilt my 1.8L and my mom wants that one on the road first. So i should have that done within the next couple of weeks. That way more $$$ can go into the Talon. I have a feeling some of my idle problem is the cause of the brake booster vacuum hose leaking. would it be ok to just pull it off while its running, and plug the hole to the intake manifold with my finger?

 

[xlMcMlx DsM]

well today i TRIED to take my car to school, but it didnt work out too well. It surges really bad, and really fast. But also that surge while giving it throttle, which shook the car REALLY bad. I only drove a block, then went back to my house because it didnt want to damage anything(more). Is that surging under load/throttle a side-effect of idle surge? My auto teachers said it could be a combination of a bad 02 sensor, and clogged fule filter. What do you guys think could be causing that surge under throttle? because if i am able to fix that, it will at least be drivable, it will just have idle surge, which i can deal with. Maybe ill take a video or something so you guys can see what i am talking about.