Help with Idle problem.
Thread Starter
Teching In
Joined: Jul 2006
Posts: 23
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Help with Idle problem. -I Know- I searched for simmilar threads but I didn't find anything exactly like my problem....
I just put a new LT1 6-speed in my car ( it has a new cc305 cam) It starts and idles just fine but has problems Maintaining an Idle while comming to a stop.
It's a little hard to explain...
Say I'm driving along, drives just fine, coming to a stop take it out of gear. RPMs drop smoothly but instead of bottming out at 900 or whatever they drop down to like 300 then bounce back up to like 1100 and it sort of yo-yo's back and forth for a second. then finaly normalize at 900. (Doesn't stall, though almost)
Could this be a Tune issue because of my new Cam? Or is there something else I should look at. (Car ran fine on old motor 3 months ago)
Thanks in advance....
I just put a new LT1 6-speed in my car ( it has a new cc305 cam) It starts and idles just fine but has problems Maintaining an Idle while comming to a stop.
It's a little hard to explain...
Say I'm driving along, drives just fine, coming to a stop take it out of gear. RPMs drop smoothly but instead of bottming out at 900 or whatever they drop down to like 300 then bounce back up to like 1100 and it sort of yo-yo's back and forth for a second. then finaly normalize at 900. (Doesn't stall, though almost)
Could this be a Tune issue because of my new Cam? Or is there something else I should look at. (Car ran fine on old motor 3 months ago)
Thanks in advance....
Thread Starter
Teching In
Joined: Jul 2006
Posts: 23
Likes: 0
Nope, no tune yet. I know it needs a tune. But first I have to break in the engine first. 500-1000 Miles.
Secondly, I want the car working correctly when I get it tuned. (I dont what to bring the car in for a tune and find out that sensor xyz is failing and it cant be tuned and waste a $400 tune)
So I guess what my question is: Is this problem most likly a TUNE issue (so I shouldn't worry) Or is this some other problem that I need to take care of before I get it tuned.
Thanks again
Secondly, I want the car working correctly when I get it tuned. (I dont what to bring the car in for a tune and find out that sensor xyz is failing and it cant be tuned and waste a $400 tune)
So I guess what my question is: Is this problem most likly a TUNE issue (so I shouldn't worry) Or is this some other problem that I need to take care of before I get it tuned.
Thanks again
Its a tune issue... The pcm is expecting a load from the converter/transmission that is no longer there with the 6spd in neutral or clutch depressed.
With an M6 tune, the pcm will use the VSS and TPS signal to determine whether the car is in gear (under load) or not. With the automatic, it uses a circuit from the shifter to tell the pcm whether the trans is in park/neutral or one of the driven gears.
If you just swapped the trans, its likely that after the tune you will notice the rpms tend to hang untill you come to a complete stop. This is because the two wires that went to the PRNDL switch to tell the pcm its position are not supposed to be there in an M6 car. Most swappers simply connect them to get the hatch release button to work again, this tells the pcm that your in neutral all the time. Even though its programming is attempting to tell it otherwise.
I never sorted the problem out in my car before going to the TH400, but Im almost positive that the hatch release and pcm signaling issue could be worked around by using the e-brake switch to connect these wires via a relay (existing circuit is used to activate the relay, in turn connecting the other wires only when needed). That way they're not connected when your driving, but will allow the hatch release to work when your stopped with the e-brake engaged.
Factory M6 cars simply use the e-brake switch and VSS to determine whether the hatch button is allowed to work or not anyway.
With an M6 tune, the pcm will use the VSS and TPS signal to determine whether the car is in gear (under load) or not. With the automatic, it uses a circuit from the shifter to tell the pcm whether the trans is in park/neutral or one of the driven gears.
If you just swapped the trans, its likely that after the tune you will notice the rpms tend to hang untill you come to a complete stop. This is because the two wires that went to the PRNDL switch to tell the pcm its position are not supposed to be there in an M6 car. Most swappers simply connect them to get the hatch release button to work again, this tells the pcm that your in neutral all the time. Even though its programming is attempting to tell it otherwise.
I never sorted the problem out in my car before going to the TH400, but Im almost positive that the hatch release and pcm signaling issue could be worked around by using the e-brake switch to connect these wires via a relay (existing circuit is used to activate the relay, in turn connecting the other wires only when needed). That way they're not connected when your driving, but will allow the hatch release to work when your stopped with the e-brake engaged.
Factory M6 cars simply use the e-brake switch and VSS to determine whether the hatch button is allowed to work or not anyway.
Oh yeah, almost forgot... The 2 wires in question I believe are the small orange and black ones that went to the factory shifter harness. If you went by the shoebox swap instructions, you probably connected them together.
