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Idle surge

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idkiliketurbos

15+ Year Contributor
820
159
Mar 2, 2009
Appleton, Wisconsin
Ok so I was doing some work and I disconnected the battery. I go to start the car up, and bam, idle surge like no other. It used to have some idle issues before i disconnected the battery but now more than ever. It will shoot up to 2000 on start up, go down very slowly, then start going from 1000 to 2000 and then drop back to 1000 and repeat the process. I am getting sick of my idle issues and what do you guys think it could be? Its a 93 motor and the works in my 97 gst by the way.
 
when you disconnect the battery your ecu will lose volatile memory and it will run a little weird until the ecu relearns how to run your motor.

have you tried fixing your idle surging problem?
 
Oh i did not know that. I have never tried to fix the problem before but if i could get it to constantly idle at about 900 or 1000 like it should I would be very happy. So i will have to let it sort of re-learn?
 
yea it may take up to 100 miles to fully relearn.
fix it!! i would start with a boost leak test
 
Alright well it got out of the phase where it would surge really high. Now it just idles really low consistantly ( about 400ish). Its better than before because it doesn't seem to fluctuate now. I think I just need to set my base idle? Sound right?
 
I havn't checked yet for boost or vacuum leaks. And ever since i bought the car it had an idle issue. Right now it is very consistant at about the 400 or 500 range so I would think that adjusting the base idle would maybe kick it up to where it needs to be.
 
That seems like a really low idle. I thought factory idle was 750. I had idle hunt 1100-1500 when car was warm. I searched and used the help of some threads I found and now am totally happy with my 750-850 idle range, and no hunting now a very steady perfect idle. The high and low's of my idle usually differ with ambient air temperature. With a low idle like that seems you have an air restriction instead of leak. Maybe a stuck throttle plate? BISS lowered to far? Misfit ISC? Tempermental TPS? And during most of the idle adjustments you MUST ground certain things. Not doing so will put undo stress on other components of your idle system.

Noticed you have a 93 swap in your 2g, your timing can mess with your idle as well. A 5 degree change in my timing cause's idle surge for me, but being set dead on my idle is great.
 
Yeah the timing job was just done before I had bought the car. I will try turning the biss out just a tad and see what that does for me. I will also clean out the throttle body this weekend to make sure the plate isn't sticking.

Update. The check engine light randomly came on and since then its been idling at about 1000. I will use my dads code reader do see what the light is for.
 
FWIW, my '91 was doing pretty much the same thing. When I had the engine resealed, I had the mechanics replace most of the vacuum lines. It made a big difference. Still does it a bit, not nearly as bad as before though.
 
^run a boost leak test like he said
do you have any disconected hoses as well?
 
Sounds more like misfire to me. I had the same problem a while back, and turns out, I had fried out one of my spark plug wires. When I went to replace them, I also noticed that my spark plugs weren't gapped right. I went ahead and bought some NGK G-powers, and new wires (Bosch 7mm Mag Core) and now the problem is solved.
 
id set the biss and than check for a vaccum leak. if anything just yank all the vaccum lines, block off the egr valve but only do that if you dont have emissions where your from
 
Hey sorry for the delayed reply guys. I have not read the code yet as I have not been able to get ahold of the code reader yet. It will still randomly pick times to fluctuate or idle low or normal or high. It makes me think it is not my biss because of how random it is. Unless the 0-ring is bad. But it sounds like either a dirty throttle body or a bad ISC. *prays its not the ISC* This weekend I am going to take the throttle body and clean it up to make sure the plate isn't sticking. I never have had a chance to do that yet.
 
B.L.T.
Ohm test ISC.
Remove FIAV & clean, or blockoff/ screw in completely.
 
Sounds exactly like my promblem. Just head to walmart and get throttle body cleaner and clean it perfectly, like everyone else said i would look the code up first
 
Well I hooked up my dad's code reader and it didn't read the code or remove the light. It did the same thing in my 98 talon last year so i'm guessing that reader won't work in these cars. Any autoparts stores that do it for free?
 
Misfire won't cause idle surge. Misadjusted BISS, boost leak, bad/dirty ISC, or burnt ECU will cause idle surge. Go through all of your tests and cleaning and then move on from there. If your surging, expect a P0505 code.
IC Pipe Tester
2G BISS Adjustment
DmTaLoN's Idle Speed Control Test/Fix Page!

I had some nasty idle surge. It would go from 900-2000 rpm's constantly while idling. The car sounded like it was pissed. Took it to AutoZone to have the code pulled, and it came out as cylinder 1 misfire. Swapped the spark plugs around, and drove til the CEL came back on. Went back, still said cylinder 1 misfire. Replaced the wires right there in the parking lot, and guess what.... idle surge was fixed.

So, yes, misfire CAN cause idle surge. All the other things you listed can also cause it too.
 
Sorry for such a delay. I did a boost leak test and found that my throttle body to intake manifold gasket is not sealing at all. Wouldn't hold hardly any pressure and you could feel the air rushing out. It has a metal gasket in there right now and my buddy gave me 2 paper gaskets for it. When I get that done hopefully I won't have a bad idle any more.
 
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