finally got my LS1 started!!! strange prob though...
Not sure where to post this, so feel free to move in appropriate forum...
After all the studying and planning and doing, my LS1 FINALLY starts up and it sounds MEAN!!! I have a weird problem though...After a while it will just start to rev on its own, I mean the rpms just keep slowly climbing from idle all the way to 2500. I tried bringing the idle screw down on my 78mm throttle body, but when I do that, the car has trouble starting.
The engine is a 98 LS1, TSP XS Series 233/239 cam, granatelli maf, TSP pcm tune.
Has this ever happened to anyone? What do I do from here?
Any chance of a vacuum leak? May be getting unmetered air into the engine somehow
To be honest, yes, there is a chance I guess. I'm pretty sure I plugged off what I needed to plug though. Where would you check first for a vacuum leak? The front of the intake manifold?
I noticed also that there is a hole in the throttle body plate.
To be honest, yes, there is a chance I guess. I'm pretty sure I plugged off what I needed to plug though. Where would you check first for a vacuum leak? The front of the intake manifold?
I noticed also that there is a hole in the throttle body plate.
the hole is supposed to be there lol.
take some brake cleaner or carb cleaner and spray around your intake manifold around the fuel injectors and tb.
I sprayed carb cleaner at potential leak spots; it did nothing to the idle. I did however, manage to lower the idle to just under 1000 by taking the throttle body idle screw almost all the way down. But, in order to start the car, I have to put my foot on the accelerator.
So I talked to TSP since they're the ones that did my pcm tune (and my cam). They said that the hole in the throttle body that I have should probably be a little bigger because what that will do is allow more air to come in on startup, but the idle should stay the same, since the pcm reads throttle position to determine how much gas to give the engine (throttle position among other things).
So it looks like I have a little drilling to do. What do you guys think?
With a cam that big you will probably have to drill the TB a little bit regardless. Doing so could keep you from having to shell out $450+ on a custom tune. Clean up the wiring and make 100% sure you don't have an intake leak before you get a custom tune.
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I sprayed carb cleaner at potential leak spots; it did nothing to the idle. I did however, manage to lower the idle to just under 1000 by taking the throttle body idle screw almost all the way down. But, in order to start the car, I have to put my foot on the accelerator.
So I talked to TSP since they're the ones that did my pcm tune (and my cam). They said that the hole in the throttle body that I have should probably be a little bigger because what that will do is allow more air to come in on startup, but the idle should stay the same, since the pcm reads throttle position to determine how much gas to give the engine (throttle position among other things).
So it looks like I have a little drilling to do. What do you guys think?
If your idle is too high, drilling the hole in the tb bigger will allow the engine to draw more air and idle even higher than before. I would (as others said) check for a vacuum leak everywhere first. Check to ensure the intake manifold is thoroughly seated EVERYWHERE. Also make sure the sensors on the back of the manifold are properly installed and necessary vacuum lines have been capped. May be worth cleaning your MAF and other air intake sensors.
If your idle is too high, drilling the hole in the tb bigger will allow the engine to draw more air and idle even higher than before. I would (as others said) check for a vacuum leak everywhere first. Check to ensure the intake manifold is thoroughly seated EVERYWHERE. Also make sure the sensors on the back of the manifold are properly installed and necessary vacuum lines have been capped. May be worth cleaning your MAF and other air intake sensors.
Just saw this right after I posted. I sprayed carb cleaner on all injectors where they went into the intake manifold, sprayed on the pcv connections, and on the throttle body to valve cover connections. It did nothing to the idle. I capped the passenger side port on the back of the intake manifold, and the other port i have my brake booster hose going to. My map sensor in the back is secured with a clamp and sealant:
I sprayed carb cleaner on the EGR plug at the front and top of the intake manifold also.
NONE of this changed the idle AT ALL. If you are convinced that I have a vacuum leak, where else should I be looking? I do NOT want to drill into my throttle body if I don't have to. I am paranoid about overdrilling.
I have a short video of what it was doing...I will try posting it to youtube soon.
I had a similar problem, but not quite as extreme. replaced the intake manifold gaskets and pcv valve and hose and it went away.
I was able to find it using brake parts cleaner and spraying around. Did you have someone watching the tach as you did it? i definitely couldn't hear a difference but the needle did jump around a tad.
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2000 trans am A4|3.23's|ssra|lid|ported tb|hooker lt's|ory|magnaflow catback|tune
35/21mm swaybars|bilsteins|hypercoils|adjustable phb|adjustable lca's|lca rb's|sfc's|tq arm 340rwhp - 355rwtq uncorrected
I had a similar problem, but not quite as extreme. replaced the intake manifold gaskets and pcv valve and hose and it went away.
I was able to find it using brake parts cleaner and spraying around. Did you have someone watching the tach as you did it? i definitely couldn't hear a difference but the needle did jump around a tad.
Ah, good point. No I did not have someone watching the tach! I was listening for a difference and didn't hear anything, like you said. My intake manifold gaskets are brand new, and my pcv valve and pcv hoses are brand new.
I know that a mail order tune isn't perfect and several people have said a dyno tune will do wonders for these engines. Even TSP said a mail order tune was to get you in the ballpark.
here's a video of how it starts and the idle just gets up to 2500 rpm without me touching it. In the video it looks like I turned the idle screw with a little allen wrench, but I couldn't get it on the screw so I actually did NOT touch the idle screw at all in this video:
Also, here's the hole in the throttle body (78mm FAST); not sure if this has been drilled out already or not. looks like a good sized hole to me, i think the stock throttle bodies' holes are much smaller, correct?:
and yeah that hole is way bigger. i threw on a ported throttle body with the hole drilled out and it raised the idle noticeably. car fought the brakes(automatic) and accelerated on it's own without hitting the gas. strange that yours is normal at first and then revs up so fast though. do you have a scanner so you can watch what the IAC is doing?
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2000 trans am A4|3.23's|ssra|lid|ported tb|hooker lt's|ory|magnaflow catback|tune
35/21mm swaybars|bilsteins|hypercoils|adjustable phb|adjustable lca's|lca rb's|sfc's|tq arm 340rwhp - 355rwtq uncorrected
and yeah that hole is way bigger. i threw on a ported throttle body with the hole drilled out and it raised the idle noticeably. car fought the brakes(automatic) and accelerated on it's own without hitting the gas. strange that yours is normal at first and then revs up so fast though. do you have a scanner so you can watch what the IAC is doing?
Two other people mentioned that it's probably the IAC also. Unfortunately I don't have anything like EFILive or HPTuners.
To throughly check for a vacuum leak also consider the brake booster and or the evaporate emmisions system for un-metered air, if possible watch the long term furl trim percentages and start pinching of VAC line i. e. to brake booster or to EVAP lines or PCV and if the idle changes or smooths out or your fuel trim (long term) starts to drop then u have isolated the concern.
finally got my LS1 started!!! strange prob though... 
01 SS Rally Red A4 #4987 
