ERATIC IDLE with a 218 comp cam

[y-hate]

Has anyone ever had any idling problems with a 218/218 comp cam? I was at a stop light and my car began to idle up and down real bad, it felt like it was going to die out until i gave it some gas... and by looking at scanmaster my IAC was at 00 and my tps. 46 it only does it when in drive or reverse any ideas also i replaced the iac with a new one, same results. What`s next?

 

[Steve Wood]

Did it do it from the beginning after you installed the cam or later?

The IAC should be set somewhere between 15-30 counts when in Park, AC off, and engine fully warm.

It should read considerably more in gear.

The tps should read no more than .46 v with the engine running and, I would set it a bit lower to leave a margin of error to prevent it from running the iac out.

If it were me, I would start with the basics, set the tps to .40-.42 and then readjust the iac to see if you can get the right counts in Park. The hotter the engine gets the lower the iacs will typically be. This is the reason the engine needs to be up to operating temperature.

When you get the iacs into range, turn the engine off and then restart to make sure the iacs reset and give you the right numbers.

 

[y-hate]

every time the car warms up the iac falls to 00 but when giving it some gas the iac count goes up then back down... it does not stay at any certain number.. what do i need to do know?

 

[Steve Wood]

When the car is fully warm, set the iac to 15-30 in Park and be sure the tps is reading no more than .46 when the engine is idling and preferable a bit less. Restart the car after the iac has been set to make sure it has reset and does not change on you.

 

[y-hate]

How do i set the iac correctly? is this what is causing the car to idle like that?

 

[Steve Wood]

May be...if it gets past zero, it can hold the throttle blad open

With the engine fully warm (I am redundant, huh?), idling in Park, no A/C, turn the iac screw on the throttle body counterclockwise until the iacs are holding around 20. Not that when you unscrew the iac screw, the tps voltage will drop. This is natural.

The iac screw is on the driver's side of the throttlebody pointing back toward the firewall. It looks like an idle adjustment screw but it is not. It may have a soft gray rubber cap pushed over it...takes a torx screw driver but I usually just grab the head with a pair of pliers and adjust it rather than looking for a short torx.

When It hits about 20 counts, kill the engine and restart to see if it stays there or very close to there.

 

[J Banning]

Good info Steve

-Banning.

 

[y-hate]

just tried to reset the iac but the highest it got was 5 this was with the screw turn in all the way. then after resetting the tps the iac drop back down to 00. i used two iac both with the same results. whats next

 

[S10xGN]

Hmmm, vacuum leak somewhere?

 

[TurboJim]

The reason IAC is 00 is because its trying to lower the idle. You said you screwed it IN. You opened the throttle. You need to back it out (close the throttle) to raise IAC. You may have to do it in increments, and/or adjust your TPS as you go. If it goes below I belive .29 it will code TPS low and run a default value which will screw you all up.

 

[y-hate]

Thanks, i guess i was doing it wrong, I will try it again after work tomorrow... I need to get it fix before Sat. going Corvette bashing in Bowling green (ZR1)

 

[Steve Wood]

to raise the numbers, one should turn the screw counterclockwise, which is "out" to me. Is that the direction you went? If so, a vacuum leak would seem possible.

What is your vacuum in gear reading at idle? Have you sprayed all possible joints with carb cleaner or similar to check for leaks?

 

[SpeednV6]

I had that cc2218/218, I did have an eratic,lopy idle. I learned that it was too big a cam for unported heads. The car did not have any low-end torque nor top end if i punched it. I switched to a cc206/206...works good.

 

[Chris McDade]

I run the comp 218/218. My car idles pretty good. I could never get it perfect. I've come to the conclusion that this big cam is not going to idle like the stock one did.

 

[Steve Wood]

Programming the in gear idle to 800 helps bring the vacuum up and smooths the idle some.

 

[Chris Taylor]

I have a Comp 212/212 and it has a somewhat rough idle.

 

[Turbo1dr]

More fuel is needed for the cam to idle smooth. A reprogrammed chip will compensate and "cover up" all that duration.

 

[Eric Stage I]

I think Steve W. is right on the money with raising the idle speed. I used to have the same 218 cam in my 4.1. Even with the extra cubes, it really needed to idle at about 900rpm to be smooth. I was using a maxeffort and it was programmed for 900 anyway, I also could richen up the idle to smooth it out also.
I switched over to an Erson 214/214 to move my powerband down slightly (I didn't want to shift at 5800, I wanted more like 5500-5600). Even with the 214, it likes the idle at 900.

Eric