leblanc1

iTrader: (2)

I have an LS2 with Maggie TVS2300 in my 68 Chevelle. Recently I've been having a fluxing RPM issue where at a stop light, it will go from 900 RPM to 500 or less, often times stalling. Sometimes, it holds rock steady at 900 RPM and all is well. This happens with the AC on or off.

I've read a lot about IAC issues maybe causing this, but I've also read that the LS2 throttle body has an integrated IAC or that it's electronically controlled and you can't just remove it to clean it.

I haven't taken the time to pull the throttle body and clean it yet, but I do plan to.

This car was dyno tuned about a year ago. No CEL's. I don't have HP Tuners and nobody local does tuning (I moved from where it was previously tuned)

Other than that, any thoughts?

leblanc1

iTrader: (2)

Nothing?

leblanc1

iTrader: (2)

So I pulled the throttle body and for all intents and purposes, it was pretty clean. Had a little bit of carbon around the butterfly. I sprayed with throttle body cleaner, wiped it all away, put it back together. It's still doing the same thing. Where else can I look? Anyone?

truckdoug

iTrader: (25)

gonna need to get more data. maybe one of those blue tooth obd2 dongles and the torque pro app?

leblanc1

iTrader: (2)

Is that the only option to pull some data? I have a Centech OBDII reader. Can that help at all?

Project GatTagO

iTrader: (7)

Do you have a VSS signal going to the ECU?

Andrew

leblanc1

iTrader: (2)

I think the only vehicle speed sensor I have is from the transmission to the Dakota Digital dash. I don't recall if there is a sensor going to the ECU.

What's your theory if there is?

Suncc49

If you don't have a vss signal going to the ecu you could have idle issues and run risk of the car shutting off randomly apparently... I used a dakota digital adapter for the speedo cable to generate mine.

leblanc1

iTrader: (2)

Well, I installed whatever came with my Dakota Digital VHX dash. I just don't recall all the connections.

Can you explain how a VSS would affect an idle issue?

ls1nova71

iTrader: (4)

Does the rpm drop while sitting at a light, or does it drop when coming to a stop? If you dont have a VSS signal going to the PCM, basically what happens is the PCM gets used to the engine running at a cruising speed then when you stop, it doesnt know the car has stopped and can cause it to stall. If its fluctuating while already stopped and nt when stopping I wouldn't think its a VSS problem. Maybe a vacuum leak or something. Have you verified your fuel pressure isnt dropping off at idle? Maybe the pump is getting weak?

leblanc1

iTrader: (2)

It happens as soon as I put the car in neutral and while coasting to a stop...it then continues to happen while stopped. Sometimes it levels out and steadies at 900 RPM, other times it continues to flux from ~400 to 900 RPM...at times dying out.

If it is a VSS issue, what is the resolution?

I will also look into a possible vacuum leak. I only have one vacuum line that's running the brake booster. Other vacuum ports are capped off.

I have not verified fuel rail pressure, I need to put a gauge on to check that, but that's a very good suggestion to look at.

leblanc1

iTrader: (2)

Some additional info: anytime I start the car fresh when it's cold...it starts right up immediately.

If the car stalls as a result of the surging at idle issue, it's a little difficult to get the car started again. Like it's taking much longer than usual to ignite and get going again. Would that be an indication more towards a fuel issue?

Project GatTagO

iTrader: (7)

This sounds like a VSS issue to me. I don't have a VSS in my GTO and it will sometimes do this exact thing. The solution is to add a VSS to the computer or blip the throttle a few times after you put it in neutral.

Funny how we get used to fancy EFI and forget how shitty carburetors could be...LOL

Andrew

leblanc1

iTrader: (2)

Can someone check me on a fuel pressure test? I hooked up a gauge, turned key to on position and I get about 55 psi or so but then it immediately bleeds down to near zero. Then I start the car and the pressure is pretty much pegging the gauge out around 90-100 psi (no fluxing RPM at this time). Then I shut the car off and it bleeds down very quickly again.

Reminder this is an LS2 with inline filter/regulator and no return line.

Is there something wrong with this test?

ls1nova71

iTrader: (4)

What are you using for a regulator? Corvette filter/regulator? If so, are you sure it's hooked up right?

leblanc1

iTrader: (2)

Yes, the stock filter/regulator combo. Keep in mind, I've been driving the car the way it its for nearly two years with zero issues until recently. It was dyno-tuned with the way it is and pulls over 600HP to the rear wheels. The filter is hooked up property without question. The real question is did the fuel pressure test fail because it didn't hold pressure at all and could it possibly be caused by a bad filter/regulator or something else? The car operates extremely well most of the time...until it doesn't.

leblanc1

iTrader: (2)

Others have mentioned that loss of fuel pressure immediately after the pump is turned off could be a symptom of the pump itself leaking inside the tank. I'm just wanting to know if my idle issue could possible be caused by this fuel pressure issue....especially being so intermittent.

Something else that came to mind...every now and then when I really want to get on the throttle, if i punch it, the engine will rev up quick...then almost immediately will kick back like it choked...then pick up again and go. Almost like misfire of sorts. This is also intermittent.

Michael Yount

iTrader: (1)

Do you have a check engine light hooked up?

leblanc1

iTrader: (2)

I sure do and I'm not getting any CEL at all.

Michael Yount

iTrader: (1)

Have you tried to pull codes?