Idle After Tune

[HGFireHazard]

I've been driving the car around since the dyno tune and she runs great, but I can't get it to idle like it did before. Last year before the S/C it would idle around 750-775 range, but now I can barely get it to fall below 1,000. I tried taking out the idle screw but it didn't seem to have any effect on the idle period. Is this something they programmed with the PCM burn? Can I change this? Also, FWIW, they also set the TPS voltage to the correct range.

 

[IEatRiceGT]

Same situation here...mine idles 1000+ after tune. It does, however, run perfectly other than that.

 

[HGFireHazard]

I think that's a little strange. It isn't a huge deal, but I got stuck in a traffic jam today and burned almost 1/4 tank of gas. Anyone have any suggestions or also have this issue? The stock cam really does sound nice with a low idle and an aftermarket exhaust.

 

[GRGT1994]

If you had a custom chip burned, I'd start with your shop. They probably did adjust it and your idle set screw (and TPS etc.) so that they all work together well. If you start messing with one end of the equation without touching the rest, you could make it worse.

Here is one low impact suggestion. Try resetting your computer (unplug for 30 min), then run the idle reset procedure (start and run for 2 minutes with no accessories, then turn on all accessories including AC and leave running for an additional 2 minutes). That might settle things back down again.

 

[HGFireHazard]

I have tomorrow off of work so I'll give them a call and ask them what's up. When I was having problems with my MAF I played with my idle screw before the tune and when I received the car back it didn't appear to have moved at all. I'll see about the idle reset tomorrow as well. I'm hoping this isn't something I have to deal with and it can be dropped down. Oh well, we'll see.

 

[smokediver27]

I may be wrong about this HG, but if I remember right, no matter what you do with the idle screw, the computer is going to try and compensate for it and override it.

 

[HGFireHazard]

I may be wrong about this HG, but if I remember right, no matter what you do with the idle screw, the computer is going to try and compensate for it and override it.

You are 100% correct. Adjusting the idle screw had no effect on my idle, period. The only thing I can think of to do is what was suggested by clearning the KAM and try doing the idle over again. If that fails I will call the shop and see what's up.

 

[GRGT1994]

Just curious. What did you find out from your tune shop?

 

[HGFireHazard]

I called them this afternoon but Paul wasn't at the shop today... figures. I got impatient and decided to play with the throttle screw and the IAC. I took it step by step starting with the throttle screw, and then taking the IAC all the way in and backing it out 1 1/2 turns, then clearing the KAM to start the learning over again. Backing the IAC adjustment out 1 1/2 turns was approximately 4/5 of a turn farther out than it was before. The results were the same, I have the exact same idle as I did before after 2 minutes no acc, 2 minutes with and 30 minutes of city driving. I didn't check the TPS voltage because it was set by the shop, but as a precaution I will check it tomorrow. As far as I can tell there isn't anything I can do, but tomorrow we'll see I guess.

 

[HISSIN50]

You guys are right - the computer can raise the idle but it has no means of making the idle lower.

I missed it if asked: does disconnecting the IAC allow the car to idle decently? If so, cleaning or replacing the IAC, along with an idle reset (like you've been doing already, but with a more functional IAC now) might help.
A restrictor plate in the IAC interface might also be something to consider.

Good luck.

 

[HGFireHazard]

Thanks hissin. I actually didn't try to unplug the IAC to see how it idled so I will give that a shot tomorrow. I'll also look into a possible restrictor. I'll do some more searching around and see if I can come up with anything. I'll be pretty bummed if there isn't a way to get the idle down. I'm just unsure as to why they would have set it so high. BTW, will TPS voltage change by me adjusting the IAC and throttle screw?

 

[HISSIN50]

BTW, will TPS voltage change by me adjusting the IAC and throttle screw?

The TPS static reading can change with adjusting the throttle stop screw. It shouldn't change with adjusting the idle-bleed screw (which is a controlled vacuum leak, rather than the mechanical throttle-blade position-change achieved with the throttle stop screw).

And since you're lowering the throttle-stop setting, I dont think that you would be able to get it out of spec (though checking it real quick once you get the issue settled is a good idea). I found that when I bottomed out my throttle stop screw a hair too far, my gas pedal would stick because the throttle blade was sticking in the TB-bore.

One last idea in case it ever comes up (I dont think it applies to you). If you have a car that idles well but at some point while driving, the idle gets high (1200-2000 RPM normally) and stays high until the car is shut off and restarted (once restarted, it idles normal till it hangs-up again and you have to recursively keep shutting it down), that's a sign of a bad TPS. I dont think it applies at all, but since your having the issues, it was worth mentioning.

Good luck bud.