Can you get idle surge from no fuel upgrades?

[16G AWD]

Ok to rephrase the question i have an evo III turbo on a jdm evo III motor with the stock injectors and stock fuel pump,and no tune done to the car yet because the motor only has 800 miles on it. Could this be the reason for my idle surge? Boost leak test comes back good i was told if you get idle surge at start up it might be the tps? I was thinking maybe it could be because i have an upgraded turbo with stock fuel and no tune. BTW im on stock 9psi.

 

[VETTE_50_TH]

It could be the tps, or isc stepper motor. It could be a lot of things. Also, if you maf is acting incorrectly. Check the isc and tps first.

James

 

[16G AWD]

Those were the two I was leaning more to. Thanks for the heads up. Im going to run to the junkyard and snatch those up.

 

[CTP]

Before you spend money on random parts, just go unplug your ISC and see if the surge stops. That will rule that out immeditately. Do the same for the TPS and rule that out as well. No need to waste money on parts that are very easy to check.

 

[-TunedDSM-]

Along with testing the TPS and ISC, check all of your vacuum lines for any leaks, cracks or missing lines.

 

[16G AWD]

Ok here's an update. I unplugged the tps and there was no difference. then i did the same thing to the Iisc, which i believe is in the back of the TB with that coolant line hooked up to it, that did nothing either. I cleaned my TB and it helped a little but still doesnt stay still. all my vacuum hoses r changed out with new ones and all zip tied. Any suggestion for next steps?? Im thinking of making a clip of cold start and letting you guys hear it. Would an exhaust leak give you issues like this? I feel air blowing right above the downpipe but i dont feel any cracks when it cools down and i touch it.

 

[CTP]

Does it only do it on cold starts?

 

[16G AWD]

No, the whole time the car is on. When i cleaned the throttle it didn't really do anything. It also idles kinda like it has cams. I unplugged the isc and it didn't do a thing, I unplugged the tps and it got worse. Im just thinking of getting another tps an see if that fixes it.

 

[CTP]

You probably should have mentioned before that it also idled rough. Any ideas on what's causing that? It's probably related to the surge.

 

[16G AWD]

Im praying it's the TPS, or ISC, then its an easy fix but if not then i dont kow..

 

[CTP]

A bad ISC won't make it idle rough. A bad TPS might, but you said you unplugged it and nothing changed so that isn't the issue either. Plugs, vacuum leaks, fuel leaks, fuel pressure, O2 sensor, mechanical timing, ignition timing... check it all.

 

[16G AWD]

No i said the TPS unplugged made it worse. Heres what whats done so far. replaced the plugs with NGK bpr7es, boost leak check, replaced all hoses and zip tied them all. It has a new o2 sensor and the head gasket is new, the motor was recently rebuilt like 700 miles ago. I would assume the timing was good since the motor was recently rebuilt but who knows. anybody have input??

 

[16G AWD]

I narrowed it down to timing, TPs, or Isc. Won't you throw a CEL if one of those sensors go out though?

 

[Freerevving]

Would an exhaust leak give you issues like this? I feel air blowing right above the downpipe but i dont feel any cracks when it cools down and i touch it.

The most common reason for idle surge on most cars is an exhaust leak before or very close to the o2 sensor.

HTH --Mac

 

[winterftbl]

If its your isc you will get a cel, at least I did. Hope that helps. I would change the tps sensor and see if that helps.

 

[16G AWD]

thanks for the info, im gonna put it on a lift at lunch. I can feel some air on the top part of the elbow of the stock pipe. But when i let the car cool down and feel, i dont feel any cracks but should i feel any air down there with the fans off??

 

[Freerevving]

thanks for the info, im gonna put it on a lift at lunch. I can feel some air on the top part of the elbow of the stock pipe. But when i let the car cool down and feel, i dont feel any cracks but should i feel any air down there with the fans off??

nope ... that's an exhaust leak. Feeling for cracks rarely works, look for black soot coming out of a crack or seal. If the leak is before your o2 (or very close) you've got the problem nailed.

Between exhaust pulses, the leak will actually pull a small vacuum. The o2 sensor reads the extra oxygen and causes the engine to way too run rich, causing the idle to rise. When the fuel injection discovers the rich condition, it will lean it out and lower the idle... then the o2 reads it lean again and you have surging.

I suggest looking for a leaking gasket, as well as a crack.

--Mac

 

[16G AWD]

I took it to my friend's exhaust place and he found the small leak and fixed it, problem is that didnt fix anything. now i notice that i sometimes backfire now when i down shift. any other ideas besides the tps? The car seems fine when im driving just when its idling. Could it be my timing needing to be adjusted?

 

[Freerevving]

timing can definitely affect it usually if it's WAY off, but engines often recover from it quickly without constant surging. If your timing was that off, you'd feel a certain loss in power...

other than that, I'd double check for exhaust leaks (even the best can miss something), test your Idle control Unit, TPS, etc... If those check out, figure out what's wrong with the fueling. One clogged injector can cause this.... Just don't go buy-and-replacing. Run tests until you know

p.s. check to see if your ground wires are good. Using a multimeter, check for resistance from different points on the engine to the chassis (and ecu wiring to chassis if you can)

 

[dsmdegier]

Check your throttle body and see if the throttle plate is stuck open just a tad. That will cause major idle surge.

 

[16G AWD]

Thanks guys..

 

[16G AWD]

i cleaned out the tb plate and still nothing.

 

[Freerevving]

timing can definitely affect it usually if it's WAY off, but engines often recover from it quickly without constant surging. If your timing was that off, you'd feel a certain loss in power...

other than that, I'd double check for exhaust leaks (even the best can miss something), test your Idle control Unit, TPS, etc... If those check out, figure out what's wrong with the fueling. One clogged injector can cause this.... Just don't go buy-and-replacing. Run tests until you know

p.s. check to see if your ground wires are good. Using a multimeter, check for resistance from different points on the engine to the chassis (and ecu wiring to chassis if you can)

yeah If you have a haynes, this shouldn't be too hard

 

[16G AWD]

I appreciate the help. I just need to get a multimeter then i can start. Im just so frustrated because the car runs great its just this idle that is bugging the crap out of me.

 

[16G AWD]

Ok I did a search and what alot of people were saying to do first is take off my tps and isc and clean them with carb cleaner and the tb and that should work. But im scared to take off the tps because i dont know how to adjust it and im sure on the location of the isc. i wanna say its the plug thats to the left of the throtthe body. I wanna do this to see if this takes care of it. Do you guys agree with this method??