Tune problem or engine problem?
Tune problem or engine problem? Car is a 2000 trans am. ws6 store hot cam 218/227 .600/.600. Have a FTI 3800 stall converter and 3.73s. PCMforless tune.
What the car is doing.... On start up 95% of the time it idles fine. When cold I can put it into drive/reverse and it idles fine, same with when its hot. I did have one hot start where the idle hunted/searched/surged. Generally giving it some throttle it will figure it out. So then when I am moving slowly with foot off brake in 1st gear once I let off the throttle the idle starts to really surge. 500rpm-1000rpm...reverse or drive. Also does it when coasting down hill in 1st or 2nd, creeping forward in traffic....Its like a huge vacuum leak. If I come to a stop slowly it will do this...if I come to a stop quickly it will not.
To me it seems like the IAC would be going nuts at this point. I have a reader that can tell me some values but I dont know if it can data log. Its just the little Torque app.
Would cracking the throttle blade open be a bad idea? Or drilling the t/b?
I will double check all my vac lines. It doesnt seem to be intake gasket problems, Ive dealt with that. Just trying to see where to start on this. What values should I be looking for with IAC or other sensors?
What the car is doing.... On start up 95% of the time it idles fine. When cold I can put it into drive/reverse and it idles fine, same with when its hot. I did have one hot start where the idle hunted/searched/surged. Generally giving it some throttle it will figure it out. So then when I am moving slowly with foot off brake in 1st gear once I let off the throttle the idle starts to really surge. 500rpm-1000rpm...reverse or drive. Also does it when coasting down hill in 1st or 2nd, creeping forward in traffic....Its like a huge vacuum leak. If I come to a stop slowly it will do this...if I come to a stop quickly it will not.
To me it seems like the IAC would be going nuts at this point. I have a reader that can tell me some values but I dont know if it can data log. Its just the little Torque app.
Would cracking the throttle blade open be a bad idea? Or drilling the t/b?
I will double check all my vac lines. It doesnt seem to be intake gasket problems, Ive dealt with that. Just trying to see where to start on this. What values should I be looking for with IAC or other sensors?
So yea that hole didnt effect anything.
This morning it was colder out and she was a bit more tempermental. Starts up and idles fine. Put it in reverse and it idles fine, give it gas to back up and then it starts surging and wanting to stall.
Noticed today it was anything from 5-30mph, over 30 and it was fine. at a stop light its fine. I dont get it.
I will crack the throttle body open a bit, but Im leaning towards intake manifold gaskets now. It got better the hotter it got, but still not right. Not sure when to say its tune related.
This morning it was colder out and she was a bit more tempermental. Starts up and idles fine. Put it in reverse and it idles fine, give it gas to back up and then it starts surging and wanting to stall.
Noticed today it was anything from 5-30mph, over 30 and it was fine. at a stop light its fine. I dont get it.
I will crack the throttle body open a bit, but Im leaning towards intake manifold gaskets now. It got better the hotter it got, but still not right. Not sure when to say its tune related.
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Joined: Oct 2014
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From: Virginia
You really need to get a data log if you can. It's pretty tough to see if your IAC is going to zero, as a guess, because this is kind of what it sounds like here. However, it could also be getting too much fuel. It could also be too much or too little spark in certain places. I do know that too much spark will cause surging on larger cams. We also call it bucking. I've had that issue on my own cars. Pulling 3-5 degrees out usually solves that problem in the affected areas, typically around 2k RPM.
It does sound like a tune issue, since as you say 95% of the time it's fine. If it were mechanical, then the problem would be much more noticeable and affected in more driving conditions. Keep in mind, idle tuning is probably the most annoying and difficult things to get right, since the amount of tables that are used to get it right and how they ALL affect each other. What that translates to is, what works in one condition doesn't necessarily work in another. Cold starts is one of those things. If it was remotely tuned, then I can 100% say it's in your tune. As stated, not their fault, since even sitting in the car and doing it in person proves difficult to get the idle just right and working in all conditions with aftermarket setups, particularly larger cams.
If you can read your O2's (assuming it's in closed loop) you can usually tell if you have a vacuum leak. Don't start tearing things apart yet or throwing parts at it until you can rule the tune out.
It does sound like a tune issue, since as you say 95% of the time it's fine. If it were mechanical, then the problem would be much more noticeable and affected in more driving conditions. Keep in mind, idle tuning is probably the most annoying and difficult things to get right, since the amount of tables that are used to get it right and how they ALL affect each other. What that translates to is, what works in one condition doesn't necessarily work in another. Cold starts is one of those things. If it was remotely tuned, then I can 100% say it's in your tune. As stated, not their fault, since even sitting in the car and doing it in person proves difficult to get the idle just right and working in all conditions with aftermarket setups, particularly larger cams.
If you can read your O2's (assuming it's in closed loop) you can usually tell if you have a vacuum leak. Don't start tearing things apart yet or throwing parts at it until you can rule the tune out.
Thanks for the reply. The intake manifold has never been off on a 19 year old car. I just dove into it last night, $30 in gaskets and I know its been done. I cant get to my friend with the data logger for a few days, but I agree its something that I need to look at. All tuners ever say is its not their tune lol. This way when they ask about gaskets I can say for sure yes they are new and good.
I know the IAC is newer but it could be failing too.
I know the IAC is newer but it could be failing too.
Last edited by trilkb; Sep 20, 2019 at 08:27 AM.
Ill have the new intake gaskets on tonight or tomorrow. will clean the MAF too. Then ill go after the tune. Ive cleaned the MAF a few times. The odd thing here is that the car idles fine when at a light or stopped in park, with a dirty MAF it didnt idle that great and it also hesitated a lot and the throttle wasnt very smooth.
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Drove the car last night with the new intake manifold gaskets. I thought it was fixed but the problem is still sort of there. Might need more driving. MAF was clean as could be.
If I'm doing 30 and put it in neutral and come to a stop it's fine. In drive It's almost like the transmission is holding the gear too long before down shifting to 2nd and 1st.
If I'm doing 30 and put it in neutral and come to a stop it's fine. In drive It's almost like the transmission is holding the gear too long before down shifting to 2nd and 1st.
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I unpluged the iac and the problem is better. So bad iac? Unplugged MAF, same issue, Tps seems to give realistic values while slowly pressing it down.
I unpluged the iac and the problem is better. So bad iac? Unplugged MAF, same issue, Tps seems to give realistic values while slowly pressing it down.
Unfortunately no. Im guessing its IAC or TPS related. But yea, diagnostic capability is limited right now. I did the intake manifold gaskets mainly because they are cheap (~$30) and I knew they probably need replaced on a 19 year old car.
[QUOTE=trilkb;20152350]Unfortunately no. Im guessing its IAC or TPS related. But yea, diagnostic capability is limited right now. I did the intake manifold gaskets mainly because they are cheap (~$30) and I knew they probably need replaced on a 19 year old car.[/QOOTE]
Smart money bets on an IAC problem. They can fail in a manner that gives what appear to be legit scanner readings while still ******* your tune.I have chased my tail on just such an issue before.
Smart money bets on an IAC problem. They can fail in a manner that gives what appear to be legit scanner readings while still ******* your tune.I have chased my tail on just such an issue before.
Well I did the iac, the one in it I think was stuck or sticking or just not moving full range. New iac made it idle super high so I did a relearn and it came down. Still surged in reverse but seemed to do better coming to a stop. The problem is going down my streer. I'll brake for an inverted speed bump then go, as I'm going downhill it shifts to 2nd, once that happens the rpms drop and then it starts the surging. I coast to my driveway and basically stop and it recovers.
So I decided I'm just going to take it to get dyno tuned. Never had a car dyno tuned before so I hope it goes well.
So I decided I'm just going to take it to get dyno tuned. Never had a car dyno tuned before so I hope it goes well.
Joined: Nov 2003
Posts: 6,216
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From: Wichita KS / Rancho San Diego
If it has been but a short time since the install of your new tune or having the battery disconnected, the lack of learned idle settings can cause idle surge and "cruise control" effect - very similar to vacuum leak symptoms. Just a thought as it has taken weeks for this to correct itself in some cases when I've done a reflash, even when I've done a relearn.
hmm, well it definitely hasnt been getting driven lately. I gotta get a trans cooler on it and get the exhaust straightened out, something moved and now on idle its hitting the body on the over the axle area. Im just hoping the tune straightens the car out and it drives and idles better. But it probably has learned some bad habbits from the old IAC.
Last edited by trilkb; Oct 18, 2019 at 09:40 AM.
Staging Lane
Joined: Oct 2019
Posts: 57
Likes: 29
My truck had a similar issue, I did the exact same suspecting the manifold gaskets and got the felpro ones but that didn't solve the issue, checked all my hoses, perfectly fine, turned out my injector orings were leaking. In gear it felt like it was cammed, idle would pick up randomly and it would surge forward on what felt like one cylinder and then return to normal for a few revs. Braking while in gear slowly felt like a warped rotor, but sudden stops and hard braking were normal. Had me going up the wall for 2 months, oring kit fixed it, although it wasn't before I gave up and took it to the dealership where they stripped out my manifold putting the fuel rail back on. The relearn should only take a short drive of getting on and off a highway, anything that gets the ECU to go between open loop and closed loop usually gets you set, easiest way to check is if your scanner will tell you that the vehicle is ready for emissions testing.